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 LATEST SYLLABUS
Note : Topics under Screen area have been deleted due to Covid-19 for 2022-23 Board Examinations.
Unit-1: Reproduction (14 M)
Reproduction in Organisms
Reproduction; a characteristic feature of all organisms for continuation of species; modes of reproduction — asexual and
sexual reproduction; asexual reproduction — binary fission, sporulation, gemmule formation, fragmentation; regeneration.
Sexual Reproduction in Flowering Plants
Flower structure; development of male and female gametophytes; pollination — types, agencies and examples; outbreeding
devices; pollen-pistil interaction; double fertilization; post fertilization events — development of endosperm and embryo,
development of seed and formation of fruit; special modes— apomixis, parthenocarpy, polyembryony; Significance of seed
dispersal and fruit formation.

Human Reproduction
Male and female reproductive systems; microscopic anatomy of testis and ovary; gametogenesis— spermatogenesis and
oogenesis; menstrual cycle; fertilisation, embryo development upto blastocyst formation, implantation; pregnancy and
placenta formation (elementary idea); parturition (elementary idea); lactation (elementary idea).

Reproductive Health
Need for reproductive health and prevention of Sexually Transmitted Diseases (STDs); birth control — need and methods,
contraception and medical termination of pregnancy (MTP); amniocentesis; infertility and assisted reproductive
technologies- IVF, ZIFT, GIFT (elementary idea for general awareness).

Unit-2: Genetics and Evolution (18 M)

Principles of Inheritance and Variations
Mendelian inheritance; deviation from Mendelism—Incomplete dominance, co-dominance, multiple alleles and inheritance
of blood groups; pleiotropy; elementary idea of polygenic inheritance; chromosome theory of inheritance; chromosomes and
genes; Sex determination — in humans, birds and honey bee; linkage and crossing over; sex linked inheritance —
haemophilia, colour blindness; Mendelian disorders in humans — thalassemia; chromosomal disorders in humans; Down's
syndrome, Turner's and Klinefelter's syndromes.
Molecular Basis of Inheritance
Search for genetic material and DNA as genetic material; Structure of DNA and RNA; DNA packaging; DNA replication;
Central dogma; transcription; genetic code; translation; gene expression and regulation; lac operon; genome and human and
rice genome projects; DNA fingerprinting.

Evolution
Origin of life; biological evolution and evidences for biological evolution—paleontology, comparative anatomy, embryology
and molecular evidences; Darwin's contribution, modern synthetic theory of evolution; mechanism of evolution — variation
(mutation and recombination) and natural selection with examples, types of natural selection; Gene flow and genetic drift;
Hardy-Weinberg's principle; adaptive radiation; human evolution.

Unit-3: Biology in Human Welfare (14 M)

Human Health and Disease
Pathogens; parasites causing human diseases (malaria, dengue, chickengunia, filariasis, ascariasis, typhoid, pneumonia,
common cold, amoebiasis, ring worm) and their control; Basic concepts of immunology — vaccines, cancer, HIV and AIDS;
Adolescence — drug and alcohol abuse.

Strategy for Enhancement in Food Production

Improvement in food production: Plant breeding, tissue culture, single cell protein, Biofortification, Apiculture and Animal
husbandry.
Microbes in Human Welfare
In household food processing, industrial production, sewage treatment, energy generation and microbes as biocontrol
agents and biofertilizers.

Unit-4: Biotechnology (10 M)

Biotechnology : Principles and Processes

Genetic Engineering (Recombinant DNA Technology).

Biotechnology and its Applications

Application of biotechnology in health and agriculture: Human insulin and vaccine production, stem cell technology,
gene therapy; genetically modified organisms — Bt crops; transgenic animals; biosafety issues, biopiracy and patents.
Unit-5: Ecology (14 M)
Organisms and Populations
Organisms and environment: Habitat and niche, population and ecological adaptations; population interactions —
mutualism, competition, predation, parasitism; population attributes — growth, birth rate and death rate, age
distribution.
Ecosystem
Ecosystems: Patterns, components; productivity and decomposition; energy flow; pyramids of number, biomass,
energy; nutrient cycles (carbon and phosphorous); ecological succession; ecological services — carbon fixation,
pollination, oxygen release (in brief).
Biodiversity and Conservation
Concept of biodiversity; patterns of biodiversity; importance of biodiversity; loss of biodiversity; biodiversity
conservation; hotspots, endangered organisms, extinction, Red Data Book, biosphere reserves, national parks,
sanctuaries.
Environmental Issues
Air pollution and its control; water pollution and its control; agrochemicals and their effects; solid waste management;
radioactive waste management; greenhouse effect and global warming; ozone layer depletion; deforestation; any one
case study as success story addressing environmental issue(s).

EXAM PATTERN
Total Marks Total
S.No. Type of questions
questions obtained marks
1. Multiple choice 04 01 04
2. Very short answer type 05 01 05
3. Short answer type 05 02 10
(25 words)
4. Short answer type 12 03 36
(30 words)
5. Long answer type 03 05 15
Total questions 29 70

1. Reproduction in Organisms (Deleted for 2020-21 Examinations) —

2. Sexual Reproduction in Flowering Plants 5-19
3. Human Reproduction 20-32
4. Reproductive Health 33-40
5. Principles of Inheritance and Variations 41-55
6. Molecular Basis of Inheritance 56-69
7. Evolution (Deleted for 2020-21 Examinations) —
8. Human Health and Diseases 70-84
9. Strategy for Enhancement in Food Production —
(Deleted for 2020-21 Examinations)
10. Microbes in Human Welfare 85-93
11. Biotechnology : Principles and Processes 94-103
12. Biotechnology and Its Applications 104-113
13. Organisms and Populations 114-125
14. Ecosystem (Deleted for 2020-21 Examinations) —
15. Biodiversity and Its Conservation 126-134
16. Environmental Issues (Deleted for 2020-21 Examinations) —
Unsolved Papers (5) 136-140
Some Important Diagrams 141-143
 5

Unit-1 : Reproduction
Chapter 1 : REPRODUCTION IN ORGANISMS
(This Chapter has been Deleted From Syllabus For Session
2020-21 Due To COVID-19 Epidemic)
Chapter

2
SEXUAL REPRODUCTION
IN FLOWERING PLANTS

² Vegetative reproduction : It is a kind of reproduction, in (usually in a test tube) from a tissue callus. These seedlings on
which the plant does not produce gametes or some specialised germination may give rise to a large population.
structure for reproduction. Simply, a vegetative part of the plant ² Polyembryony : The occurrence of more than one embryo in
body (such as root, stem, leaves, twig etc.), gets detached from a seed is called polyembryony. [Students should note that in
the main body and develops into a new plant. polyembryony, normal gamete formation and fertilisation are
² Sexual reproduction : Sexual reproduction is a kind of involved, but the unusual feature is only the presence of more
reproduction, in which two parents (one male and other than one embryo, per ovule (seed)].
female) are involved in the formation of new individuals. These ² Sexual incompatibility : Stigma receives a variety of pollen
parents produce gametes (specialised haploid cells), which on grain but not all pollen grains succeed to germinate and bring
fertilisation, give rise to new individual. The individual is called about fertilisation. Stigma is so equipped as to allow only right
hybrid. kind of mating types (pollen grains) to germinate over it. The
² Androecium : The male reproductive whorl of the flower is other pollen grains, which fail to germinate on a stigma, are
called androecium. Its units are called stamen. Each stamen said to be incompatible to it (stigma). This phenomenon is
consists of a filament and anther. Anther contains known as ‘sexual incompatibility’.
microsporangia, which produce microspores of pollen grains. ² Microsporogenesis : The formation of microspores or pollen
² Gynoecium : The female reproductive whorl of the flower is grains is called microsporogenesis. In this process, the
called gynoecium. Its units are called carpels (or pistils). Each microspore mother cells (which are diploid) divide by meiosis
carpel consists of a stigma, style and ovary. Ovary contains to give rise to haploid microspores. This process takes place in
ovules or megasporangia, which produce megaspores. microsporangia (within the anther).
² Apomixis : The substitution of normal sexual reproduction by ² Embryo sac : The mature female gametophyte in
another form of reproduction that does not involve meiosis angiosperms is known as embryo sac. In a typical plant, it
(R.D.) and syngamy (fertilisation) is called apomixis. In other contains 7 cells and 8 nuclei. These include 3 antipodal cells, 2
words, the reproduction without fertilisation is called apomixis. synergid cells, 1 egg cell and 2 polar nuclei in the centre of the
Plants showing this phenomenon are called apomict. main cell.
² Parthenogenesis : It is a type of apomixis, in which an ² Pollen grain : The microspores are also called pollen grains. A
embryo develops from an unfertilised egg cell. This egg cell is pollen grain represents the first cell of the male gametophyte.
derived from a sporogenous tissue. On maturation, it gives rise to mature male gametophyte.
² Micropropagation : It is an advance method in tissue culture ² Pollination : The transfer of pollen grains from anthers to the
technology, in which many small seedlings are produced stigma of a carpel is called pollination. It is carried out by many
types of agencies, such as wind, water, insects etc.
 6

Multiple Choice Questions 1 Mark

Q.1. The entry of pollen tube through integument is called : Q.14. Pollination in Salvia is performed by : (2019)
(2017) (a) Water (b) Air
(a) Chalazogamy (b) Porogamy (c) Insects (d) None of these
(c) Both of these (d) Mesogamy Q.15. In an angiospermic plant stamens are : (2019)
Q.2. Polyembryony was discovered by : (2017) (a) Female reproductive organ
(a) Leeuwenhoek (b) Maheshwari (b) Male reproductive organ
(c) Winkler (d) Noll (c) Both (a) and (b)
Q.3. The process of double fertilization was discovered by (d) None of these
(a) Strasburger (b) Robert Koach Q.16. Transfer of pollen grains from the anther to the stigma
(c) Nawaschin (d) Drouchet of another flower of the same plant is called : (2019)
Q.4. Rafflesia is pollinated by: (a) Autogamy (b) Geitonogamy
(a) Elephant (b) Butterfly (c) Xenogamy (d) Cleistogamy
(c) Tsetse fly (d) Carrion Fly Q.17. A typical angiosperm embryo sac, at maturity, is :
Q.5. Pollination by bats is called : (2019)
(a) Chiropterophily (b) Entomophily (a) 7-nucleated, 8-celled (b) 7-nucleated, 7-celled
(c) Ornithophily (d) Malcophily (c) 8-nucleated, 7-celled (d) 8-nucleated, 8-celled
Q.6. The development of seedless fruit is known as: Q.18. In a typical angiospermic pollen sac the number of
(a) Herkogamy (b) Parthenocarpy microsporangia is : (2019)
(c) Morphogenesis (d) Parthenogenesis (a) 1 (b) 2
Q.7. Double fertilization means : (2017) (c) 3 (d) 4
(a) The fusion of two male gametes with egg Q.19. Father of Indian Embryology is called : (2019)
(b) One male gametes fuses with the egg and the other (a) Sir Jagdish Chandra Bose
with secondary nucleus. (b) Prof. Panchanan Maheshwari
(c) One male gametes fuses with the egg and other (c) Dr. Hargovind Khurana
with synergid (d) Dr. Birbal Sahni
(d) All of these Q.20. How many meiotic divisions are required to produce
Q.8. The point where the funicle is attached to the body of 200 microspores from functional microspore mother
the ovule is called: cells? (2019)
(a) Chalaza (b) Hilum (a) 400 (b) 50
(c) Nucleus (d) Micropyle (c) 200 (d) 100
Q.9. When the anthers mature before the stigma, it is known Q.21. Which one is helpful in the formation of egg-
as : apparatus? (2019)
(a) Dicliny (b) Heterostyly (a) Egg
(c) Protandry (d) Protogyny (b) Egg and synergids
Q.10. Process of double fertilization occurs in : (2008, 14, 16) (c) Egg and antipodals
(a) Algae (b) Angiospermic plants (d) Synergids and antipodals
(c) Gymnospermic plants (d) Fungi Q.22. In which of the following insects pollination takes
Q.11. Antipodal cells are located at : (2018) place? (2020)
(a) Chalazal end (b) Micropyler end (a) Gurhal (b) Fig
(c) Centre (middle) (d) None of these (c) Wheat (d) Hydrilla
Q.12. The antipodal cells are those which are present : (2018) Q.23. Chalaza is found in : (2020)
(a) At chalazal end (b) At micropylar end (a) Pollen grain (b) Ovule
(c) In the center (d) None of these (c) Embryo sac (d) All of these
Q.13. Embryo culture was I st proposed by : (2018) Q.24. If the cells of any plant’s leaf have 24 chromosomes
(a) Hanning (1904) then what will be the number of chromosomes in its
(b) Heberland (1902) endosperm? (2020)
(c) Maheshwari and Guha (1964) (a) 12 (b) 24
(d) Scoog and Millar (1957) (c) 36 (d) 48
 7

Q.25. Which of the following part of angiospermic plant is (a) Root (b) Leaf
haploid? (2020) (c) Male gamete (d) Zygote

Answers
1. (d) 2. (a) 3. (c) 4. (d) 5. (a) 6. (b) 7. (b) 8. (b) 9. (c) 10. (b)

11. (a) 12. (a) 13. (a) 14. (c) 15. (b) 16. (b) 17. (c) 18. (d) 19. (b) 20. (b)
21. (b) 22. (b) 23. (c) 24. (c) 25. (c)

Very Short Answer Type Questions 1 Mark

Q.1. Name the parts of an angiosperm flower in which Q.9. Give two examples of water pollinated plant.
development of male and female gametophyte take Ans. Vallisnaria and Hydrilla.
place? Q.10. What are fruits?
Ans. Development of male gametophyte takes place in Ans. Fruits is ripened ovary enclosing the seeds. The ovary
anther before pollination and on stigma after wall develops into pericarp. In some fruits the calyx,
pollination. Development of female gametophyte takes corolla and thalamus also take part in the development
place in ovule. fruit. Such fruits are called as false or spurius fruits.
Q.2. What is the meaning of cleistogamy? (2014) Q.11. What is syngenesious condition? (2018)
Ans. Flowers which always remain closed and do not Ans. Syngenesious or synantherous is a type of arrangement
blossom are called cleistogamous flower. These are of stamen on flower. In it, all anthers are limited, but
self pollinating flowers, e.g., Commelina, groundnut their filaments remain free. It is a characteristic feature
etc. of family—compositae (sunflower).
Q.3. How many nuclei are found in polygonum type embryo Q.12. What is called gynandrous condition? (2017)
sac? (2006, 17) Ans. In gynandrous condition, the stamen and pistils fused
Ans. Polygonum type of embryo sac is 8-nucleate. together to form a column, e. g., Orchid.
Q.4. What is pollination? Q.13. How many meiotic division need to form 100 grains of
Or Define the pollination? (2020) wheat or barley?
Ans. The process of transfer of pollen grains, from an anther Ans. 125 meiotic division.
to the stigma of the same flower or of different flower is Q.14. Draw a labelled diagram of a germinating pollen grain.
called pollination. (2019)
Q.5. What is Geitonogamy? Ans. See Long answer type question-2.
Ans. The transfer of pollen grains from an anther to the Q.15. Write the names of two seeds in which endosperm is
stigma of different flower of the same plant is called consumed by the developing embryo before seed
Geitonogamy. (self pollination). It occurs in maturation. (2019)
monoecious plants. Ans. Gram and Pea.
Q.6. What is polyembroyony? (2011, 14) Q.16. Name the cells inside a mature pollen grain. (2019)
Ans. Polyembryony is the phenomenon of development of Ans. Microspore mother cells.
more than one embryos in a seed. It was discovered by Q.17. Draw a labelled diagram of a longitudinal section of a
Leeuwenhoek in 1719 in citrus. Mango fruit. (2019)
Epicarp
Q.7. Define the term xenia and metaxinea?
Ans. Xenia: It is the direct effect of pollen on the endosperm Mesocarp
Ans.
character of a plant. Foeke describe this phenomenon
Endocarp
for the first time.
Metaxenia : The direct effect of pollen on structure Seed
Q.18. Draw the diagram of a normal embryo-sac. (2019)
outside the embryo sac is called as metaxenia. Swingle
Ans. Please see the Fig. of Short answer type question-7.
reported the effect of pollen on the character of seed
Q.19. Give the name of any two plants in which aquatic
coat pericarp.
pollination take place? (2020)
Q.8. What is seed?
Ans. As a result of double fertilization many changes are Ans. Lotus and lily.
brought about in the ovule due to which ovule is Q.20. Give any two examples of false fruit? (2020)
converted to seed. Ans. Mango and Apple.
 8

Short Answer Type Questions 2 & 3 Marks

Q.1. Mention the advantages of cross pollination? Ans. (i) Unisexuality or Dicliny: In unisexual flowers
Ans. (i) It helps to eliminate bad characters from the race. stamens and carpals are found in different
(ii) It helps in the development of new characters due flowers. It is called unisexuality or decliny. It can
to recombination of genes. be of two types:
(iii) Vigour and Vitality of the race increases. (a) Monoecious plants: When male and female
(iv) Immunity to diseases increases. flowers are born on the same plant, e.g.,
(v) Ability to adopt according to changing Maize, cucurbits, castor.
environment increases. (b) Dioecious plants: When male and female
Q.2. Give characteristics of insect pollination flowers? flowers are born on the different plants, e.g.,
Ans. Pollination by insects is called Entomophily. Insects Carica papaya, Canabis savita.
which help in pollination are bees, flies, wasps, moths (ii) Pollination in Maize: In maize, pollens are large
and beetles. Insect pollination flowers show following and heavy. When mild wind shakes the male
characters. inflorescence to release the pollen, they fall down
(i) Flowers are brightly coloured. vertically. The cluster of male flowers are born
(ii) Pollen grains are sticky or with spinous exine. terminally and the female inflorescence are born
(iii) Stigma is also sticky. laterally at lower levels. The silk of cobs (style,
(iv) A sugar fluid called nectar is secreted in many stigma) projects beyond protective leaves. Pollen
plants. grains fall upon the stigma and pollination takes
(v) Flies are mainly attracted by the unpleasant smell place.
of flowers such as Rafflesia and Staplia ( Rooting Q.6. Differentiate the following: (2014)
meat) and Aristolochia (Decaying tobacco) etc. (i) Embryo sac and endosperm
Q.3. Explain briefly the process of double fertilization in (ii) Self and cross pollination.
angiospermic plants. (2009, 10, 12, 13, 14) Ans. (i)
Ans. After discharge from pollen tube one of the male Embryo sac Endosperm
gamete fuses with the egg and forms the oospore 1. Embryo sac is haploid It is triploid (3n).
(zygote). This is called true fertilization (syngamy). (n).
The second male gamete fuses with the secondary 2. It develops from It develops from
nucleus (2n) and forms a triploid (3n) nucleus called as functional megaspore. endosperm nucleus.
Primary Endosperm Nucleus (P.E.N). This is called 3. It nourishes the It nourishes the
triple fusion. Thus there are two acts of fusion. This is endosperm and embryo. developing seeds and
called double fertilization. embryo.
Zygote produced, as a result of syngamy develops into 4. Food is not stored in it. Food is stored in it.
embryo and the triploid nucleus develops into the (ii)
endosperm which is used for nutrition of embryo.
Self pollination Cross pollination
Q.4. Write the significance of double fertilization.
Ans. Double fertilization was discovered by Nawaschin in 1. Transfer of pollen grains Transfer of pollen
from anther to the grains from anther to
1898. stigma of same flower is the stigma of flower of
The significance of double fertilization are as follows: called self pollination. different plant.
(i) The endosperm produced supplies food material 2. Flowers are bisexual. Flowers are often
to the developing embryo. unisexual.
(ii) The endosperm in angiosperms develops after 3. Plants do not have to Plants have to depend
fertilization. depend on pollinating on pollinating
(iii) Embryo is differentiated properly leading to the agencies. agencies.
formation of healthy seeds. 4. Only a small number of Large number of
pollen grains are pollen grains are
(iv) This saves the energy which might go waste with required. required.
unfertilized ovule as in gymnosperms.
5. Flowers are devoid of Flowers are colourful
Q.5. Write short note on the followings: colour and fragrance. and fragrant.
(i) unisexuality or dicliny.
6. Immunity to diseases Immunity to diseases
(ii) pollination in maize decreases. increases.
 9

Q.7. Briefly comment on longitudinal section of mature Ans. Pollination by wind is called anemophily.
ovule. (2015) Anemophilous flower produces enormous amount of
Or Write a short note on anatropous ovule. (2017) pollen grains. The pollen grains are small, light,
Ans. Anatropous (inverted) ovule: The body of the ovule smooth and dry. In some plants as in Pinus pollen
is completely inverted so that micropyle and hilum grains are winged. The flowers may be born on long
come to lie very close to each other. e.g., all plants, of axis. The anthers are versatile so as to oscillate in all
gamopetalae and majority of angiosperms. direction. Such flowers have adequate devices to catch
Structure: The mature ovule is differentiated into a the air borne pollen grains. For this the stigma is
large centrally located embryo sac which is usually usually large and feathery.
8-nucleated and 7-celled surrounding the embryo sac is Q.10. Mention the significance of dispersal of fruits and
a multicellular nucleus (2n). Enclosing the nucellus are seeds?
1 or 2 integuments (2n). The integuments surround the Ans. Dispersal of seeds and fruits is found in all the fruit and
nucellus from all the sides except at the apex of ovule, seed bearing plants. There is a great importance of
forming a pore called micropyle. The base of the ovule dispersal of seed and fruits. If we imagine the
from which integuments arise is called chalaza. The conditions when there would not be any dispersal, then
ovule is attached to the placenta by a slender stalk there would have been following odd situations.
known as funicle. The point of attachment of the body (a) All the fruits and seeds might have fallen and
of the ovule to its stalk is known as hilum. heaped on the parental bed and germinate to
3 Antipodals develop into plants of the same type.
Chalazal end (b) Similar plants have similar requirements, so there
Nucellus
might be a strong intra specific competition.
(c) Due to struggle for existence no plant would have
2 polar nuclei
developed properly.
Synergids (d) Crowed seedlings might not get sufficient
minerals, space for root and shoot development.
(e) A plant species may be extinct due to any natural
Egg cell hazards.
Micropylar end (female gamete)
Q.11. Make diagram of transverse section of mature anther.
(a) (b)
(2010, 15, 17, 19)
Fig. (a) L.S. of mature ovule (b) Mature embryo sac
Ans.
Q.8. Give the contrivances (adaptation) for self pollination? Vascular supply
(2017) Epidermis Endothecium
Ans. For self pollination following adaptation are found in
plants.
1. Bisexuality (hermaphroditism): It is only in
bisexual flowers that self pollination can take Stomium
place.
2. Homogamy: Both sex organs of a flower should
mature at a time. Pollen-
3. Cleistogamy: In some plants like Commelina, Pollen-
grains
Arachis; Oxalis the anthers mature and burst grains
Degenerating middle layers
liberating their pollen grains in a closed flower. Fig. T.S. of mature anther
This is called cleistogamy. In such plants self
pollination is the only method of pollination. Q.12. Draw labelled diagrams of nuclear and cellular
Q.9. Write short note on anemophily. endosperm. (2018)
Or Give the characteristics of anemophilous flowers. Ans. Please see the Short answer question-27.
(2019) Q.13. Draw a labelled diagram of chalazal fertilisation.
(2018)
 10

Ans. (iii) It can produce disease-resistant plants.

(iv) Offsprings produced through this are more
Chalaza adaptive to the diverse environment.
(v) Since two genetically different parents are
involved new varieties or species are formed.
Pollen Demerits of Cross-Pollination:
tube
(i) Cross-pollinated plants are always hybrid.
(ii) Cross-pollination requires a medium, external
agencies or factors without which the process
cannot occurs.
(iii) Expression of harmful characters is possible in the
offspring.
Q.17. Draw a labelled diagram of an ovule of an
Stalk
angiospermic plant. (2019)
Ans. Please see the ans of NCERT exercise question-4.
Fig. Chalazal fertilisation Q.18. Describe in brief the structure of microsporangium
Q.14. What is vivipary germination? (2019) with the help of labelled diagram. (2019)
Ans. Vivipary germination : In viviparous germination the Ans. Structure of a Microsporangium (mature anther):
seeds get germinated being attached to the parent plant. A typical microsporangium is surrounded by four wall
The embryo grows out of the seed and then out of the layers, i. e., the epidermis, endothecium, middle layers
fruit and projects out as a seedling with roots and and the tapetum.
hypocotyl. Viviparous plants produce seeds that The outer three wall layers are protective in function
germinate before they get detach from the parent plant. and help in dehiscence of anther to release pollen
This phenomenon is commonly observed in mangrove grains. Middle layer also store food during early stages
( e. g., Rhizophora species). The seedling germinates of microspore development.
and grows under its own energy while still attached to Epidermis Vascular strand
its parent. Endothecium Tapetum

Q.15. What do you mean by fleshy or succulent fruits.

Describe their importance. (2019)
Ans. Fleshy or succulent are simple fruits in which the
Middle
pericarp usually forms the pulp. The tissue of the layer
pericarp is parenchyma as it is soft. In fleshy fruits the
pericarp and accessory parts develop into succulent Pollen
tissues, as in orange and strawberries. mother cells
Importance Fig. Structure of microsporangium (a mature anther)
(i) These fruits protect seeds during development.
(ii) These fruits attracts birds and other animals to eat Tapetum is the innermost layer which nourishes the
seeds, which is useful for seed dispersal. developing microspores or pollen grains. The cells of
Q.16. What is cross-pollination? Describe its merits and tapetum possess dense cytoplasm and generally have
demerits. (2019) more than one nucleus.
When the anther is young, a group of compactly
Ans. Cross-pollination (Allogamy) : In cross- pollination,
pollen grains of a flower reach to the stigma of another arranged homogenous cells called the sporogenous
plant of the same species. It involves use of plants of tissue occupies the centre of each microsporangium.
the same species to produce seeds. Pollen grains Q.19. Explain double fertilisation. (2019)
require some agencies to reach the stigma. Ans. Double fertilization: Please see Short answer type
Merits of Cross-Pollination : question-3.
(i) Harmful characters can be isolated. Q.20. Development of female gametophyte. (2019)
(ii) It yields healthy and good offsprings and they Ans. Development of female gametophyte : Please see
have increased hybrid vigour. Long answer type question-3.
 11

Q.21. Explain with the help of diagrams, how pollen grains Ans.
develop from a functional microspore mother cell? Endospermic Non-endospermic
(2019) Endosperm is not Endosperm is completely
Ans. Please see Long answer type question-1. completely used by the used by the developing
Q.22. Write only two characteristics features of a fleshy fruit developing embryo, so a embryo before the maturation
portion of it remains in the of seed, so there is no
and draw the labelled diagram of a vertical section of a seed. endosperm left in the seed.
mango fruit. (2020)
Examples coconut castor Examples pea, bean and
Ans. (i) Fleshy fruits produce plentiful flesh. and maize. mustard.
(ii) Fleshy fruits are considered to be ready for
consumption. Q.25. Explain the development of male gametophyte. (2020)
For figure see Very short answer question-17. Ans. Please see the answer of Long answer question-1.
Q.26. Draw only a line diagram of development of a female
Q.23. Write a shert note on pollen culture. (2020)
gametophyte. (2020)
Ans. Pollen culture (microspore culture) is a technique in
Ans. Please see the diagram given in Long answer
which haploid plants are obtained from isolated pollen
question-3.
grains while in anther culture those are obtained from
Q.27. Describe the diffevent types of endosperms. (2020)
pollens, by placing anthers on a suitable, synthetic
Ans. On the basis of development in angiospermic plants,
culture medium. endosperms are of following types—
The technique was discovered by Guha and (i) Nuclear Endosperm
Maheshwari (1964). It is one of the various tissue (a) In such type of endosperm, nucleus divides
culture techniques or methods used. Progeny but cell wall does not form. Many nuclei are
developed by this technique contains a single set of formed from primary endosperm nucleus
chromosomes. through repeated divisions.
Procedure for In-vitro Pollen culture : (b) A vacuole is formed inside the endosperm,
Collection of anthers—Preferably should be taken which later degenerates and many nuclei and
from plants grown under controlled conditions or may cytoplasm fill inside it. After that many cells
be taken from plants grown in the field. are formed in this. This type of endosperm is
Transfer of anthers to the culture medium—Flower present in the member of Polypetalae class.
buds of the appropriate developmental stage are Embryo
collected and surface sterilized. Anthers from the buds Central vacuole
are excised and placed horizontally on surface (or
partially embedded) on culture medium. It is important
to note that injury to anthers may induce callus (a) Nuclear endosperm
formation from anther walls. To avoid this, small
Free nuclei
anthers are cultured as such and sometimes entire Embryo

inflorescence is cultured. Nucellus

Pollens are isolated either by squeezing or float
culturing of anthers :
Chalazal
Culture Medium for Pollen culture : chamber
Pollen can be cultured on a suitable medium containing
(b) Cellular endosperm (c) Helobial endosperm
sucrose (usually 2-3%), iron, vitamins, hormones etc.
Fig. Types of endosperm
The hormonal component of the medium is important
for initiation of growth. Usually to the culture medium (ii) Cellular Endosperm : In this type of endosperm,
auxin, cytokinin etc. are added either singly or in each nuclear division of endosperm nucleus
follows cell wall formation. This type of
various combinations.
endosperm is present in Gamopetalae class.
Low concentration of auxin stimulates callus
(iii) Helobial Endosperm
formation. In a medium supplemented with auxin,
(a) This is middle stage between nuclear and
formation usually occurs at a faster rate.
cellular endosperm. In this, cell wall is
Q.24. Difference between endospermic and non-endospermic formed after each division of endosperm
seeds with suitable examples. (2020) nucleus, but after that there is free nuclear
division, e. g., Arimura.
 12

(b) Cells of endosperm are generally formation. This process is called apomixis, e. g.,
isodiametric and they store food in large lemon, Opuntia etc.
quantity. Endosperm has thin wall but Significance—
sometimes it becomes thick due to deposition (i) It is a cheaper and cost effective method of
of hemicellulose. producing hybrid seeds.
Q.28. Explain the development of embryo of angiospermic (ii) It is easy to maintain hybrid characters intect as
plant. (2020) characters segregate during meiosis.
Ans. Please see the Answer of LA Question-2. (iii) It is a type of asexual reproduction.
Q.29. What is apomixis and what is its significance? (2020)
Ans. Sometimes embryo and sporophyte develop without
fusion of male and female gametes or without gamete

Long Answer Type Questions 5 Marks

Q.1. Describe main events during development of male Microsporangial initial/

gametophyte from microspore? (2009, 10, 11) archesporial cell
Or Explain the process of microsporogenesis in
angiosperms? (2009, 10, 11, 14, 16)
Ans. Microsporogenesis : Development of microspores (a)
from microspore mother cells or the sporogenous tissue Primary sporogenous cell
is called microsporogenesis. Microspores are Primary parietal cell
(b)
filled/developed within the microsporangium. A
typical microsporangium is surrounded by four wall Parietal tissue
layers, i.e., the epidermis, endothecium, middle layers
and the tapetum. The outer three wall layers are
protective in function while tapetum nourishes the
Vascular
developing microspores or pollen grains. (c) supply
Epidermis
Microspore mother cells divide by reduction division Endothecium (d) Tapetum
to form microspores. The division may be of :
(i) Successive type: Each of the two nuclear divisions
are followed by the formation of wall. The pollen
tetrad thus produced is called isobilateral tetrad. It
generally occurs in monocots. Middle
layer
(ii) Simultaneous type : Division occurs
simultaneously and centripetally dividing the
cells into four parts with the formation of furrows. Pollen
mother cells
The pollen tetrad thus produced is called (e)
tetrahedral tetrad. It generally occurs in dicots. Fig. Developmental stages of Anther
Development of Male Gametophyte: Development (A) Development before pollination or In-situ
of male gametophyte starts when the pollens are within development: The microspore represent first cell
the anther lobes. But when half of the germination gets of male gametophyte. It consists of a centrally
completed, the anther dehisces and the germinating situated nucleus, dense cytoplasm and two
pollens get pollinated. Further development of male distinct walls, the outer exine and the inner intine.
gametophyte takes place on the stigma. At certain points the exine is absent, these points
In this way the development of the male gametophyte are called germ pores.
involves following steps: Before discharge from the microsporangium, the
(a) Development of male gametophyte before nucleus divides forming a small cell called
pollination generative cell which is adjacent to spore wall.
(b) Dehiscence of anther and liberation of developing The remaining part of microspore is fitted with a
pollens. cell called vegetative cell. In this two celled stage,
(c) Pollination containing vegetative cell and a germinative cell.
(d) Development after pollination.
 13

Generative cell divides mitotically, to form two mitotically to form two haploid male
elongated, haploid male gametes. Pollen grains gametes.
are usually released from the anther and reaches (ii) Formation and growth of pollen tube. The
the stigma of the carpel. exine of the pollen now ruptures and the
Cytoplasm Tube nucleus cytoplasm of the vegetative cell bulges out
Nucleus through germ pore in the form of a tube,
Exine called pollen tube. Pollen tube at the apex
Intine contains tube nucleus and 2 male gametes.
Tube cell
Generative Usually, a single pollen tube arises from one
(B)
cell pollen grain are called monosiphonous, but some
(A) Germ pore
(A microspore) (C)
plants are polysiphonous, e.g., develop more than
one pollen tubes such as 10 pollen tubes in Althea
rosea and 14 in Matira neglecta.
Generative cell
Pollen tube
Germ pore
Generative Tube
nucleus Male cells nucleus
Pollen
tube Tube Two male
nucleus (A) gametes
(E)
(D) Generative
Fig. Different stages of development of male gametophyte cell (C)
(B)
before pollination
(B) Dehiscence of Anther: When pollens get Pollen
tube Tube
matured they exert some pressure on anther wall. Tube nucleus
nucleus Germinating
Consequently, the wall of the anther gets burst pollen grain
and sets free the germinating pollen grains. It
Fig. Different stages of development of male gametophyte
takes place in four different ways, in different after pollination
plants. Q.2. What is double fertilization and triple fusion? Explain
(i) Transverse: Occurs by the formation of the structure formed after syngamy.
transverse slits, e.g., Labiatae family. Or Describe with the help of labeled diagram the post
(ii) Porous: Occurs by the formation of a small
fertilization changes occurs in angiospermic plants?
opening at the apex of anther, e.g.,
Ans. Double fertilization: (see short answer type
Solanaceae family.
(iii) Valvular: Valves or window like openings question-3.)
develop for dehiscence, e.g., Lauraceae Stigma
family. Male gametes
(iv) Longitudinal: It is the most common method
of dehiscence, where longitudinal slits are
formed, e.g., Gossipium, Hibiscus etc.

Transverse Porous Valvular Longitudinal

Fig. Types of dehiscence of anther
(C) Development after pollination: It involves
Fig. Showing process of fertilization
following steps.
(i) Formation of male gametes. After pollination Post Fertilization changes :
the male gametophyte is usually at two cell 1. Embryo and its development(Embryogeny):
stage. It contains a vegetative and a After some rest period zygote develops into
generative cell. The generative cell contains embryo. A zygote divide transversely to form two
a large amount of protoplasm. It now divides cells, the one which lies towards the interior of
embryo sac is called terminal cell (embryonal
14

cell) and the other basal cell (suspensor cell) Structure of a typical monocotyledons embryo:
which is towards micropyle. The terminal or o Embryos of monocotyledon passess only one
apical cell divide vertically. The suspensor cell cotyledon. It is generally called scutellum.
divides by several transverse divisions forming a o The cotyledon is situated towards one side of
5-10 celled suspensor. The uppermost cell of this the embryonal axis.
suspensor swells up to form a haustorial cell. The o At its lower end, the embrynal axis has the
lowermost cell of suspensor is called hypophysis. radicle and root cap.
This cell gives rise to the apex of radicle. The
o The radicle and root cap remain packed in a
suspensor is destroyed after the formation of
protective undifferentiated sheath called
radicle.
coleorhiza.
Suspensor
cells o The portion of the embryonal axis above the
level of attachement of cotyledon is called
epicotyl.
(A)
Zygote o Epicotyl has a shoot apex called plumule.
Suspensor o The plumule bears a few leaf primordia
cells
Basal enclosed in a hollow foliar structure called
cell
Hypophysis coleoptile.
Terminal Q.3. What is megasporogenesis? Describe development of
cell
(B) (C)
Octant female gametophyte in angiospermic plants. (2010, 11)
(D) Dermogen
(Embryonal cell) (E) Or Describe the development of a general 8-nucleate
embryo sac with the help of diagram.
Haustorial Or Describe process of megasporogenesis
cell
angiospermic plants.
Ans. Megasporogenesis: Formation of megaspores from
Suspensor (H) megaspore mother cell as a result of reduction division
Suspensor is called megasporogenesis. Either hypodermal cell at
Hypohysis Cotyledons Cotyledons the apex of nucellus functions directly as megaspore
cells
mother cell or this cell first divides into the outer
parietal cell and an inner megaspore mother cell.
Structure and development of female gametophyte
(F) (G) (I) (embryo sac)
Fig. Stages of embryonic development in dicot plant The first meiotic division of megaspore mother cell is
In the mean time two cells formed from terminal always transverse. Second meiotic division is also
cell divide by a transverse division forming four transverse resulting in a linear tetrad of megaspore.
embryonal cell. These 4 cells divide by another Generally the lowermost megaspore is functional. The
vertical division forming 8-cells. 4-cells at the upper three megaspore degenerate. The first division of
apex give rise to plumule and cotyledons. Four functional megaspore gives rise to two nuclei, the
cells in between epibasal cells and suspensor give second division results in one pair of nuclei at each
rise to hypocotyl and most of the radicle. end, and the third division produces 4 nuclei at one end
The entire structure is called pro-embryo. Now and four on the other end.
this structure grows further and becomes heart Three of the nuclei at the micropylar end become
shaped. organized to form egg apparatus. At the chalazal end of
In dicots, two cotyledons are formed, but in the developing embryo sac three nuclei differentiate as
monocots only one cotyledon develops. By the antipodal cells. The two polar nuclei from opposite
time, the integuments of the ovule become hard ends migrate into the centre and remains unfused till
and are called seed coat and the entire ovule is triple fusion but may fuse prior to that giving rise to
now called seed. secondary nucleus.
This type of development is normal type or polygonum
type.
 15

Primary parietal Parietal cells

Archesporial cell cells 1898 in Lilium and Fritillaria. The most important and
Primary unique characteristic feature of angiosperms is the
sporogenous participation of both male gametes in the act of
cell
fertilisation.
The pollen tube releases the two male gametes into the
(A)
cytoplasm of one of the synergids, then the penetrated
(B) (C)
Parietal cells
synergid starts degenerating. One male gamete fuses
Parietal cells
with the egg cell to form a diploid (2n) zygote. This
process is called syngamy or generative fertilisation.
The diploid zygote finally develops into the embryo.
The second male gamete fuses with the two polar
nuclei or secondary nucleus in the central cell to form
Megaspore
Dyad cells Megaspore the triploid Primary Endosperm Nucleus (PEN).
mother cell(D) (F)
(E) tetrad This process is called triple fusion as three haploid
Fig. Development of female gametophyte nuclei are involved in the fusion.
After triple fusion, the central cell becomes the
Q.4. Describe the process of fertilization in Angiosperms Primary Endosperm Cell (PEC) which gives rise to
with the help of suitable diagram. (2019) the endosperm, while the zygote develops into the
Or Define the dauble fertilization and explain it with embryo. As both the fusions, syngamy and triple
suitable diagram. (2020) fusion, occur in an embryo sac, the phenomenon is
Ans. Process of fertilization in Angiosperms: The process termed as double fertilisation.
was demonstrated for the first time by Nawaschin in
Mature pollen grain
Sperm cells

Tube cell nucleus

Empty pollen grain

Pollen grain Tube cell
Stigma Sperm cells (male gametes)
Generative Tube cell nucleus
Tube cell cell Style Carpel
Antipodal cells Pollen tube
Embryo sac
Ovary
Ovule
Growth of
Embryo sac
pollen tube
Secondary nucleus
containing two nuclei
Pollination
Antipodals

Primary endosperm

Mother cell after

triple fusion

1st male gamete Secondary

1st male gamete nucleus

2nd male gamete Egg cell

Syngamy + triple fusion Pollen tube
Synergids
Release of sperm cells or male
gametes within the embryo sac
Double fertilisation

Fig. The process of fertilisation and double fertilisation

Q.5. Describe a typical angiospermic ovule with diagram. (i) Each ovule is attached to the inner wall of the
(2019) ovary (placenta), by a slender stalk, called
Ans. For Structure of Ovule : See NCERT question-4. funicle.
 16

(ii) The point of attachment of ovule to its funicle is Such plants produce nectars, fragnant and
called hilum. brightly coloured flowers etc. to attract
(iii) Main body of the ovule is formed by inner central pollinators.
mass, i. e., nucellus. Nucellus consists of living (ii) Cheiropterophily : The pollination that is
parenchymatous cells. facilitated by bats.
(iv) In mature ovules, the nucellus serves to cover and (iii) Malacophily : The pollination performed by
provide nutrition to the embryo sac (female snails and slugs, seen in some water plants.
gametophyte). (iv) Ornithophily : The pollination performed by
(v) Each ovule has two distinct ends—(a) micropyle birds. The flowers of such plants are large,
end (it is also called opening of ovule. It is the end bright coloured, odourless.
wherefrom the pollen tube usually enters the (v) Anemophily : The pollination performed by
ovule during fertilisation) and (b) Chalazal end wind (air).
(the posterior end, opposite to micropylar end). The flowers are inconspicuous and not
(vi) Externally the nucellus is covered by one or two showy. They are devoid of fragrance and
protective covers, called integuments. These nactar. Wind pollinated flowers often have a
single ovule in each of their ovaries. It is
integuments arise from the chalazal end.
found in commonly in grasses, most cereals
(vii) When only one integument is present, the ovule is
and plam etc.
called unitegmic, and if the ovule consists of two
integuments, it is called bitegmic. Very rarely
tritegmic (with three integuments) is present in
plants like Asphodelus. In some plants such as
Santalum, Olax etc, ategmic (no integument)
condition may be present.
(viii) In mature ovules, the female gametophyte or
embryo sac is present in the centre. The embryo
sac consists of egg cell (female gamete), synergid
cells, antipodal cells and polar nuclei.
Please see for figure NCERT question-4.
Q.6. Describe the germination of pollen grains on stigma
with the help of labelled diagram and also mention the Fig. Various types of pollination
fusion of male and female gametes. (2019) Advantages of Cross-pollination :
Ans. Germination of Pollen Grains on Stigma : (i) Harmful characters can be isolated.
Please see Long answer type Ques. 1(c) and 2 (ii) It can produce disease-resistant plants.
Q.7. What is pollination? Describe various kinds of (iii) It yields healthy and good offsprings and
pollination that occur in flowering plants. Mention they have increased hybrid vigour.
about the biotic pollinating agents. (2019) Disadvantages of Cross-pollination:
Ans. Pollination : Transfer of pollen grains from the anther (i) Cross-pollinated plants are always hybrid.
of the stamen to a receptive stigma of the pistil is called (ii) Expression of harmful characters is possible
pollination. in the offspring.
Types of pollination : Pollination is following two (iii) Cross-pollination requires a medium,
type— external agencies.
(a) Cross-pollination or Allogamy— In cross- (b) Self-pollination or Autogamy— The pollination
pollination, pollen grains of a flower reach to the achieved when pollen from the anthers of a flower
stigma of another plant of the same species. It is transferred to stigma of the same flower.
involves use of plants of the same species to Self pollination can be of two types; autogamy
produce seeds. Pollen grains require some and geitonogamy.
agencies to reach to the stigma. 1. Autogamy : This pollination found in bixual
Biotic Agents for Cross-pollination: These flower. The stigma of a flower is pollinated by its
include living agents for pollination. These are of own pollen.
following types: Autogamy is further classified into :
(i) Entomophily : The pollination facilitated by (i) Homogamy: The anthers and stigma matures
insects like ants, wasps, bees, butterflies etc. at same time to facilitate autogamy.
 17

(ii) Cleistogamy: The flowers never open up and o In grasses and orchids, seeds are very small and
anthers dehisce inside to ensure self light in weight and can be easily dispersed by
pollination. wind.
2. Geitonogamy: The pollination where the (ii) Water :
pollen grains from the anther of a flower are o Water is an effective method of seed and fruit
transferred to the stigma of another flower borne dispersal in plants, which are found in water or
on the same plant. grow near the banks of water bodies.
Q.8. Describe the methods of seed dispersal. (2019) o Coconut (Cocos) and Double coconut (Lodoicea
Ans. Methods of Seed Dispersal : Such seeds and fruits maldivica) have spongy and fibrous outer walls for
have to germinate and develop under limited food easy floating. Double coconut is a native of
supply. But to solve this problem, there are many Seychelles islands but due to dispersal, its fruits
devices to disperse fruits and seeds to distant areas. may reach even the coastal regions of India. Lotus
Some important devices are wind, water and animals has spongy thalamus, which help in effective
(insects and birds etc.). floating.
(i) Wind :
o Water lily has small seeds with airy aril, which
o It is the most important and effective agency for
help in floating.
fruit and seed dispersal.
(iii) Animals :
o The dispersal by seed is very effective in those
o Animals mainly the insects and birds are also very
species where fruits and seeds are light in weight.
effective means of dispersal of fruits and seeds.
o Sometimes, fruits and seeds have some accessory
o Fruits and seeds which have appendages like
parts, which also help in dissemination. For
bristles, hooks, spines and stiff hair etc., get
example—the seeds of Drumstick and Cinchona,
attached to the body of insects, hairy and wooly
and fruits of Yam, Maple and Sal have thin, flat
animals and are carried away by them to long
and membranous wings, which help them to float
distances.
in air.
o Fruits of Xanthium and Urena have curved hooks
o In members of family Asteraceae, the calyx is
for dispersal.
modified into thin hairy structures called pappus.
o Spear grass has a bunch of stiff hair which are
These pappus persist in fruits and become umbrella
helpful in dispersal. Tribulus has sharp and rigid
like. They also help the fruits to float in air.
spines that help in dispersal. Sticky hairs are found
o In some plants such as Poppy and Prickly Poppy
in Boerhavia which assist in dispersal.
(Argemone), at the time of dehiscence of the fruits
o Many edible fruits such as grapes, guava, fig, plum
the seeds are naturally thrown away. Seeds of some
etc., are dispersed by birds and even by human.
plants like Alstonia, Calotropis and Gossipium
have hairy covering which also help in the
effective dispersal of seeds.
NCERT Fully Solved Exercise
Q.1 Name the parts of an angiosperm flower in which involves meiotic cell division. The cells formed as a
development of male and female gametophyte take result of this process are called pollen grains.
place. Formation of megaspore is called megasporogenesis. It
Ans. (a) Development of male gametophyte takes place in takes place within ovule. It also involves meiotic cell
anther (before pollination) and on stigma (after division. The cell formed as a result of this process is
pollination). called megaspore.
(b) Development of female gametophyte takes place Q.3 Arrange the following terms in the correct
in ovule (inside ovary). developmental sequence :
Q.2 Differentiate between microsporogenesis and Pollen grain, sporogenous tissue, microspore tetrad,
megasporogenesis. Which type of cell division occurs pollen mother cell, male gametes.
during these events? Name the structures formed at the Ans. The correct developmental sequence is :
end of these two events. Sporogenous tissue, pollen mother cell, microspore
Ans. Formation of microspores (pollen grains) is called tetrad, pollen grain and male gametes.
microsporogenesis. It takes place within anthers. It
 18

Q.4 With a neat, labelled diagram, describe the parts of a chasmogamous. Since they are fully exposed, there are
typical angiosperm ovule. greater chances of cross pollination.
Micropylar But in cleistogamous flower, the flower remains closed
end
and do not open at all. So, always self fertilisation
Integuments
occurs. Cross pollination can not occur in such cases.
Ans.
Funiculus Q.8 Mention two strategies evolved to prevent
self-pollination in flowers.
Embryo sac Ans. Plants have developed many out-breeding devices to
(female
gametophyte) check self pollination and ensure cross pollination.
Nucellus Two such devices are—dichogamy and herkogamy.
Dichogamy involves the maturation of male and
Chalazal
end female organs at different time. In these cases, pollen
release and stigma receptivity do not occur at the same
Fig. Different part of angiospermic ovule time. Either the pollen is released before the stigma
Q.5 What is meant by monosporic development of female becomes receptive or stigma becomes receptive much
gametophyte? (2020) before the pollen release.
Ans. Four megaspores are formed in an ovule as a result of In some other species, the anther and stigma are placed
meiosis in megaspore mother cells. In many cases, out at different positions so that the pollen cannot come in
of these four megaspores, 3 undergo degeneration. So, contact with the stigma of the same flower.
entire female gametophyte is developed from only one Herkogamy : In this case stigma is longer than
(remaining) megaspore. Such a development of female stamens, so that pollens do not fall on stigma of its own
gametophyte is called monosporic development. flower, e. g ., Gloriosa.
Q.6 With a neat diagram, explain the 7-celled, 8-nucleate Q.9 What is self-incompatibility? Why does self-
nature of the female gametophyte. pollination not lead to seed formation in
Ans. In angiosperms, a typical female gametophyte (or self-incompatible species ?
embryo sac) consists of 7 cells. These include, an egg Ans. Self-incompatibility is a genetically governed
cell (female gamete), 2 synergids, 3 antipodal cells and mechanism to prevent self-pollination. In these cases,
a central cell. All cells bear a single nucleus except the the pollens of a flower are unable to germinate over the
central cell which bears two nuclei (called polar stigma of the same flower. This is because of some lock
nuclei). In this way, the female gametophyte consists and key type chemical relationship between pollen and
of 7 cells and 8 nuclei. the stigma. Genetically, pollens of the same flower are
Chalazal end
3 Antipodal unable to germinate on the stigma of the same flower.
cells
So, self-pollination does not lead to seed formation in
self-incompatible species.
Q.10 What is bagging technique? How is it useful in a plant
2 polar
nuclei breeding programme ?
Ans. In case of artificial fertilisation, or in case of cross
Central
cell
fertilisation in a bisexual plant, the stigma is covered
with a small cap of suitable size to prevent any
1 Egg cell
unwanted reaching of undesired pollens. This covering
2 Synergids
of stigma to check contamination is called bagging.
Q.11 What is triple fusion? Where and how does it take
place? Name the nuclei involved in triple fusion.
Filiform
apparatus
(2019, 20)
Micropylar end
Ans. The fusion of a sperm with two polar nuclei (secondary
Fig. Female gametophyte
nucleus) is called triple fusion. It is called so as it
Q.7 What are chasmogamous flowers? Can cross- involves the fusion of three nuclei. It takes place inside
pollination occur in cleistogamous flowers? Give the ovule in female gametophyte (embryo sac).
reasons for your answer. Q.12 Why do you think the zygote is dormant for sometime
Ans. Chasmogamous flowers are those flowers, in which, in a fertilised ovule ?
the anther and stigma are fully exposed to the external Ans. In most of the plants, zygote remains dominant for
pollinating agencies. Most of the flowers are sometimes i.e., it does not start divisions in a fertilised
 19

ovule. This is because, initially there is no endosperm Ans. A true fruit is one which is developed from fertilised
which can provide nourishment to the developing ovary. In case of apple, the fruit is formed by fleshy
embryo. So, only after the formation of endosperm, thalamus. Due to this reason, fruit of apple is called a
zygote starts division and forms an embryo. false fruit.
Q.13 Differentiate between : Q.15 What is meant by emasculation? When and why does a
(a) hypocotyl and epicotyl plant breeder employ this technique ? (2020)
(b) coleoptile and coleorrhiza Ans. To carry out cross-pollination artificially, in a bisexual
(c) integument and testa plant (which does not show above adaptation), its
(d) perisperm and pericarp stamens are removed (cut off) before flowering. This is
Ans. (a) Hypocotyl and epicotyl : Hypocotyl is the called emasculation.
cylindrical portion below the level of cotyledons, Q.16 If one can induce parthenocarpy through the
while epicotyl is the portion of embryonic axis application of growth substances, which fruits would
above the level of cotyledons. you select to induce parthenocarpy and why ?
(b) Coleoptile and coleorrhiza : Coleoptile is a Ans. For inducing parthenocarpy we can select banana
hollow foliar structure which encloses shoot apex because naturally it contains very small seeds. So,
and leaf primordial. On the other hand, inducing seedlessness may be an easier task in such
coleorrhiza is the undifferentiated sheath that fruits.
encloses radicle and root cap, at the lower end of Q.17 Explain the role of tapetum in the formation of
embryonic axis. pollen-grain wall.
(c) Integument and testa : The enclosing covers of Ans. Tapetum is the innermost layer of the
the unfertilized ovule are called integuments. microsporangium, situated in the anther. The cells of
After fertilisation, the integuments become hard the tapetum are usually binucleate. Tapetum nourishes
and are called testa. the developing pollen grains and helps in the formation
(d) Perisperm and pericarp : Remnant of nucellus of pollen wall.
in a seed is called perisperm. On the other hand, Q.18 What is apomixis and what is its importance ?
the outer layer of the fruit (ovary) wall is called Ans. Please see the Answer of SA Question-29.
pericarp.
Q.14 Why is apple called a false fruit? Which part(s) of the
flower forms the fruit ? ccc
 20

Chapter

3 HUMAN REPRODUCTION

² Fertilisation: The fusion of male and female gametes and ² Primary Sex Organs: The sex organs which produce
mixing of their nuclei is called fertilisation or syngamy (syn = gametes and sex hormones, are called primary sex organs. In
fuse). This process results in the formation of zygote. male, these are testes, while in female these are ovaries.
² Self-fertilisation: In this type of fertilisation, the male and ² Secondary Sex Organs: These are the sex organs, which
female gametes of the same individual fuse to form zygote. This play important role in reproductive process but do not produce
is a very primitive type fertilisation. It is found rarely in some gametes and sex hormones. The secondary sex organs of human
hermaphrodite animals. It is evolutionary not suitable. male are — Seminal vesicle, prostate gland, epididymis, vas
² Cross Fertilisation: It is an advance type of fertilisation, deferens and penis etc. The secondary sex organs of human
where the gametes of two different individuals (one is female female are fallopian tubes, uterus, vagina, and vulva.
and other is male), are fused to form zygote. It is found in ² Graafian Follicle: In the first 14 day of each menstrual cycle
majority of the animals. in female, a primary oocyte starts its development, under the
² Isogamy: When the male and female gametes are identical in effect of FSH. The surrounding granulosa (follicular) cells also
shape and size, they are called isogametes. These are rarely develop simultaneously. The entire structure becomes a large
found in some animals, such as Monocystis (a protozoan). follicle. This follicle is known as Graafian follicle. Its outer
² Anisogamy (Heterogamy): When male and female gametes layers form estrogen hormone. Interiorly, the follicle contains
are different in shape and size, these are called heterogametes maturing ovum (female gamete). There is also a large fluid
(anisogametes). These are found in almost all animals. filled cavity, in the centre of Graafian follicle. This cavity is
² Bisexual (Monoecious or Hermaphrodite): When both called antrum.
type of (male and female) sex organs are present in same ² Corpus Luteum: After ovulation, the remaining portion of
individual, the animal is called bisexual or hermaphrodite or Graafian follicle develops into an important endocrine gland,
monoecious, e. g . , Earthworm, Leech. called corpus luteum. The growth of corpus luteum is controlled
² Unisexual (Dioecious): In majority of the animals, male and by LH hormone (of pituitary). Corpus luteum secretes
female reproductive organs are present in different individuals progesterone hormone. If fertilisation fails to occur, the corpus
(of the same species). Such individuals are called unisexual or luteum degenerates by the end of the menstrual cycle, leaving a
dioecious. small scar, called corpus albicans. But if fertilisation occurs, the
² Conjugation: It is a temporary union of two individuals of corpus luteum continues to grow through out the pregnancy,
same species for the purpose of transfer of genetic material. It is under the effect of hCG (human chorionic gonadotropin).
not a true sexual reproduction as there is no gamete formation. ² Ovulation: The release of ovum, from Graafian follicle is
It is found in small protozoan animals like Paramecium. called ovulation. It usually occurs on the 14th day of menstrual
² Spermatogenesis: Formation of sperms is called cycle. At the time of release, the ovum is in secondary oocyte
spermatogenesis. It occurs in testes of male individual, under condition.
the effect of pituitary hormones, mainly the FSH and LH. It ² Leydig Cells: These are specialised interstitial cells, which are
involves a meiotic division and therefore the sperms are haploid present in the germinal epithelium, scattered between the
structures. follicular cells of testes. The growth of these cells is under the
² Oogenesis: Formation of female gametes (or ovum) is called effect of LH (ICSH) hormone of pituitary glands. These glands
oogenesis. It occurs in the ovary of the female individual. It is a secrete male sex hormone or testosterone.
very long and discontinuous process. It starts in the embryonic ² Sertoli Cells: These are large sized cells present in the
stage, but gets completed in adult stage (after puberty). germinal epithelium of testes. These cells are also called nurse
 21

cells. These cells serve to provide nutrition to the developing ² Cortical Reaction: As soon as the first sperm enters the
sperms. These cells also release in important hormone, called ooplasm, the zona pellucida changes chemically and becomes
inhibin, which by feedback mechanism, controls the secretion of impermeable for other sperms. This is called cortical reaction
testosterone. (zona reaction). Thus only one sperm enters the ovum
² Cumulus Oophorus: Inside Graafian follicle, the maturing (Monospermy).
ovum is surrounded by zona pellucida (mucopolysaccharide ² Extra-embryonic Membranes: Foetal membranes are 4
layer) and two to three layers of granulosa cells, which form specialised membranes, which are derived from the
corona radiata. The ovum, together with its surrounding extra-embryonic portion of blastocyst (trophoderm). Therefore,
membranes is known as cumulus oophorus. these are also called extra-embryonic membrane. These
² Decidua: When implantation of embryo in the uterine wall membranes, in general, protect the embryo, form placenta and
occurs, the endometrium of uterus undergoes tremendous provide nutrition. But these do not form any part of the body of
changes. It is now known as decidua. It is divisible into three the proper embryo. After the birth of the baby, these membranes
parts — (i) Decidua basalis (the part between embryo and outer are discarded off. Four types of foetal membranes are—Yolk sac,
wall of uterus), (ii) Decidua capsularis (the part between the amnion, chorion and allantois. These are found in reptiles, birds
embryo and uterine cavity) and (iii) Decidua parietalis and mammals only. Hence these animals are collectively known
(remaining part of endometrium). as amniotes.
² Cervix: The neck of the uterus that opens into vagina is called ² Placenta: It is a physiological connection between mother and
cervix. Its outer margin is called external os, while the inner developing embryo. It serves to provide nutrition to developing
margin is called internal os. embryo. Besides it also maintains gaseous exchange between
² Sperm Capacitation: When sperms enter the uterus, they maternal and foetal blood. It also drains the excretory wastes of
face the resistance offered by the endometrium and cilia of the embryo. Placenta is found in higher mammals only
fallopian tube. To face this resistance and reach the ovum some (Subclass—metatheria and eutheria).
of the sperms undergo certain changes. These changes are ² Parturition: The birth of baby, i.e., its expulsion from mother’s
collectively referred to as sperm capacitation. These involve the body is called parturition. At the time of parturition, uterus
increase in metabolic rate, vigorous movement of sperm tail and contracts rhythmically and propels the baby outwardly. Cervix
exposure of hyaluronidase (sperm lysine). and vagina dilate to maximum making the birth passage easier.

Multiple Choice Questions 1 Mark

Q. 1. Menstrual flow occurs due to lack of : Q. 7. Acrosome of sperm is formed from:

(a) Progesterone (b) FSH (a) Nucleus (b) Mitochondria
(c) Oxytocin (d) Vasopressin (c) Mitochondria (d) Golgi complex
Q.2. The hormones testosterone, estrogen, and corticle are Q. 8. Glands secreting male sex hormone are:
example of : (2014, 18) (a) Leydig cells (b) Somniferous tubules
(a) Lipid (b) Steroid (c) Vasa differentia (d) Testes
(c) Lecithin (d) Wax Q. 9. Estrogen is secreted by:
Q. 3. The embryo at 16-celled stage is known as: (a) Corpus luteum (b) Membrana granulosa
(a) Morula (b) Gastrula (c) Pituitary (d) Germinal epithelium
(c) Blastula (d) Blastomere Q.10. Eggs of placental mammals are of which of the
Q. 4. Fertilization of egg by sperm in the female genital tract following type:
takes place in: (a) Mesolecithal (b) Alecithal
(a) Uterus (b) Ovary (c) Telolecithal (d) Polylecithal
(c) Vagina (d) Oviduct Q.11. In a woman during implantation embryo is in : (2019)
Q. 5. The process by which ova are formed is known as: (a) Morula stage (b) Blastula stage
(a) Oviparity (b) Ovulation (c) Gastrula stage (d) Neurula stage
(c) Oviposition (d) Oogenesis Q.12. Chromosomes are formed by : (2019)
Q. 6. First or tree milk is called : (a) Euchromatin (b) Heterochromatin
(a) Rostrum (b) Colostrum (c) Both (a) and (b) (d) None of these
(c) Cholesterol (d) Baby's milk
 22

Q.13. Androgens secreted from : (2020) (c) Spermatids (d) None of these
(a) Leydig cells (b) Sertoli cells

Answers
1. (a) 2. (b) 3. (a) 4. (d) 5. (d) 6. (b) 7. (d) 8. (d) 9. (a) 10. (b)
11. (b) 12. (c) 13. (a)

Very Short Answer Type Questions 1 Mark

Q. 1. What is sexual dimorphism? Ans. Von Baer.
Ans. When male and female individuals of a species can be Q. 10. How do leydig cells help in spermatogenesis? (2011)
distinguished on the basis of their distinct Ans. Leydig cells produce male sex hormone, called
morphological features, the phenomenon is called testosterone, which is essential for the execution of
sexual dimorphism. spermatogenesis.
Q. 2. What is clone? Q. 11. Where does fertilization normally take place in human
Ans. Genetically similar copy of organism is called clone. female? (2016)
Q. 3. What is conjugation? Ans. Fallopian tubes
Ans. It is a temporary union of acellular protist for the Q. 12. What is corpus luteum?
exchange of genetic material conjugation is not a true Ans. It is the remaining part of Graafian follicle in luteal
sexual reproduction because it does not involve any phase which acts as an endocrine gland.
gamete formation e. g., Paramecium. Q. 13. Name two sex hormones secreted by human females?
Q. 4. Name the accessory genital glands in human male? Ans. Oestrogens and Progesterone.
Ans. Accessory genital glands in human male are prostate, Q. 14. What is menstrual cycle? (2019)
seminal vesicle and cowper's glands. Ans. It is a reproductive cycle in female primates, e. g.,
Q. 5. What is capaciation? monkeys, apes and human beings. In females the
Ans. In the female genital tract spermatozoa undergoes a menstruation is repeated at an average interval of about
process of changes which make them more vigorous 28/29 days.
and motile. It is called capaciation. Q. 15. Name the testicular hormone synthesized and secreted
Q. 6. Name extra embryonic membrane? by Leydig cells. (2019)
Ans. There are four types of extra embryonic membrane Ans. Testosterone.
yolk sac, amnion, chorion, and allantois. Q. 16. Write down the name of the process by which Graafian
Q. 7. What is placenta? follicle bursts and release secondary oocyte from the
Ans. Placenta is a physiological connection between ovary. (2019)
maternal and foetal tissues. It provides nutrition, Ans. Ovulation.
respiratory gases to the embryo. It also drains the waste Q. 17. Write two main functions of testis. (2020)
material from embryo. Ans. (i) Sperms formation.
Q. 8. What are primary sex organs? (ii) Secretion of testosterone hormone.
Ans. The organs which are involved in gamete formation Q. 18. Define the spermetogenesis. (2020)
and sex hormones production are called primary sex Ans. The formation of sperms (male gametes) is called
organs. spermetogenesis. This procers take place inside the
Q. 9. Who is called father of modern embryology? testis.

Short Answer T
ype Questions 2 & 3 arks
M
Q. 1. What is polyspermy? reaction or zona reaction. Thus only one sperm enters
Ans. As soon as the first sperm enters the Ooplasm, the zona the ovum ( monospermy ). When more than one sperm
pellucida changes chemically and becomes reaches in the ooplasm phenomenon is given
impermeable for other sperms. This is called cortical polyspermy.
 23

Q.2. Draw a labeled diagram of section through mammalian Q.5. What are the similarities in spermatogenesis and
ovary. (2008) oogenesis? (2010, 11, 14, 16)
Ans. Ans. 1. Both process comprise there, almost similar main
phases, viz, multiplication growth and maturation
phase.
2. In the multiplication phase in both process, the
primordial germinal cells of testes and ovaries,
proliferate mitotically.
3. In the growth phase the gonial cells accumulate
food reserves and grow to primary gametocytes.
4. Maturation phase in both comprises two
successive divisions first meiotic and second
Fig. A section of mammalian ovary
meiotic divisions.
Q. 3. Draw a labeled diagram of human sperm: (2011, 19 ) Q. 6. What is oestrous cycle?
Ans. Ans. It is homologous to menstrual cycle in non- primates
Acrosome mammals. It occurs only during breeding season. On
the basis of occurrence oestrous cycle may be of two
Head Haploid nucleus
types.
Proximal centriole 1. Monoestrous: Only one cycle in whole breeding
season, e.g., dog.
Distal centriole
2. Polyestrous: Many cycles in one mating season
Middle Spiral mitochondrial having short intervals, e.g., rats, mice, guinea pigs
piece sheath
etc.
Ring centriole In oestrous cycle, the follicles develop but ova are not
(annulus) released from follicles until the copulation takes place.
Tail Oestrous cycle consists of four phages :
1. Proestrous: It is a preparatory stage. The follicles
are maturing and secrete oestrogens. Uterus and
Tail
vagina become congested and secrete a clear
sanguinous fluid.
2. Oestrous: This is called period of heat. At this
time, there is a strong urge in the female animals
Fig. Human sperm due to the rising level of estrogen. If fertilization
Q.4. Give the differences between spermatogenesis and takes place, placenta forms and pregnancy begins.
oogenesis? 3. Mesoestrous: It is called as luteal phase. The
Ans. newly formed corpus luteum secretes
progesterone.
Spermatogenesis Oogenesis
4. Anoestrous: It is a passive asexual phase. The
1. Occurs in testes Occurs in ovaries female becomes passive and does not receive the
2. Spermatogonia are Oogonia are formed in male. It lasts upto the next mating season.
formed in multiplication phase.
multiplication phase.
Q.7. What is oogenesis? Given a brief account of
oogenesis? (2010, 19)
3. Spermatogonia store The food reserve
some food during accumulated in oogonia is Or What is oogenesis? Explain with diagram. (2020)
growth phase but this mostly yolk. Ans. Please see the Q.12 of NCERT exereise for diagram see
is never yolk. long answer question-3.
4. Both maturation First maturation division Q. 8. What is ovulation?
divisions are may be completed in the Ans. Discharge of ovum from the ovary into the oviduct is
completed in testes. ovaries, but 2nd one is
completed outside ovaries called ovulation. It occurs on the 14th day of the cycle
after fertilization bigins. by the luteinizing hormone.
5. Daughter cells formed Daughter cells formed in The ripening of the egg and its release from the ovary is
in each maturation each maturation division controlled by two important hormones secreted by the
division are similar. are dissimilar. pituitary gland, FSH and LH. In the initial stage of
 24

menstrual cycle , the secretion of FSH is very high. Q. 11. Draw a labelled diagram of female reproductive system
This hormone help in the growth and ripening of in human.
Graafion follicle and maturation of ovum. During Ans. See the Long answer type question-5.
secretory phase, the secretion of LH becomes very Q.12. Draw a labelled diagram of male reproductive system
high. This hormone promotes the ovulation and also in human.
promotes the growth of corpus luteum. Ans. Please see the answer of long question no.4.
Q. 9. What do you mean by puberty? Q.13. Difference between male and female secondary sexual
Ans. The onset of sexual functionality in organism is called charaeters. (2019)
puberty. The age of puberty in human males ranges Ans. Main differences between male and female secondary
between 11 to 14 year. But in women ranges between sexual characters are given in following table.
10 to 12 years. S. Male secondary Female secondary
Puberty in male. In males, puberty is characterized by No. sexual characters sexual characters
following changes. 1. More pronounced body Less pronounced body
1. Rapid growth of secondary sex organs such as hair characteristics (in hair characteristics
penis, seminal vesicle, vas deferens, prostate etc. beard, chest hair, etc.). (mostly in pubic
region).
2. Appearance and growth of axillary and pubic hair.
3. Apperance of moustaches and beard. 2. Heavy musculature Lighter musculature
deepening of voice, high pitched voice
4. Cracking of voice. angular features rounded (i.e. soft facial
5. Testes become functional and start producing narrowing of hips. features, wider hips for
gametes. child bearing).
Puberty in female:
Q.14. Draw a neat and labelled diagram of L.S. of human
1. Appearance and growth of axillary and pubic hair.
seminiferous tubules which show the process of
2. Growth and enlargement of breasts.
spermetogenesis. (2020)
3. Depening of voice. Pitch become high.
Ans. Seminiferous tubules are found in testis.
4. Skin texture become soft. Seminiferous Leydig
5. Ovaries become functional and start producing Spermatocyte tubules cells
gametes.
Q. 10. Write short note on the followings:
(i) Parturition (2011) (ii) Lactation
Ans. (i) Parturition: The expelling of the fully formed
young from the mother's uterus after the gestation
period ( about 40 weeks) is called parturition. Sperms
Parturition is induced by a complex
neuroendocrine mechanism. The signals are
Sertoli
initiated from the fully developed foetus and the cell
placenta. These signals cause mild contraction in
the uterus and these contractions are called foetal Fig. Transverse section of Human testis
ejection reflex. These reflex then trigger the Q.15. Give a short note on placenta. (2020)
release of oxytocin from pituitary gland. Oxytocin Ans. After implantation, finger-like projections appear on
cause the uterus to contract and labour pain the trophoblast called chorionic villi which are
begins. This propels the baby towards vagina. surrounded by the uterine tissue and maternal blood.
(ii) Lactation: 1-3 days after the baby is born, the The chorionic villi and uterine tissue become
breasts begin to secrets milk. Thus lactation interdigitated with each other and jointly form a
describes the secretion of milk from the mammary structural and functional unit between developing
glands and the period of time that a mother embryo (foetus) and maternal body called placenta.
lactates to feed her young. The placenta facilitate the supply of oxygen and
Milk synthesis is stimulated by the pituitary nutrients to the embryo and also removal of carbon
hormone prolactin (PRL) and its release from the dioxide and excretory/waste materials produced by the
breast is stimulated by oxytocin. Milk contains embryo. The placenta is connected to the embryo
valuable proteins and antibodies. The early milk is through an umbilical cord which helps in the transport
called colostrum which is very rich in calories, of substances to and from the embryo. Placenta also
proteins and antibodies. It provides natural acts as an endocrine tissue and produces several
immunity.
 25

hormones like human chorionic gonadotropin Q.16. Draw a neat and labelled diagram of male (human)
(hCG), human placental lactogen (hPL), estrogens, reproductive system. (2020)
progestogens, etc. In the later phase of pregnancy, a Ans. See the answer of L.A. question-4.
hormone called relaxin is also secreted by the ovary. Q.17. Draw a lebelled diagram of internal structure of female
We remember that hCG, hPL and relaxin are produced reproductive system. (2020)
in women only during pregnancy. Ans. See the answer of L.A. question-5.

Long Answer Type Questions 5 Marks

Q.1. Write short notes on the following :

(i) Cleavage (ii) Implantation
(iii) Blastulation (2011) (iv) Gastrulation
Ans. (i) Cleavage: Cleavage was first observed by
Swammerdam in 1738 in the egg of frog. It can be
defined as 'the process of progressive subdivision
of the zygote by mitotic cell divisions into an
increasing number of cells of progressively
decreasing size. It results in the formation of a
Fig. Implantation 6 days after fertilization
solid ball like mass of cells, called morula.
Type of cleavage: On the basis of amount and
distribution of yolk, cleavage can be of following
types.
1. Holoblastic equal cleavage: The cleavage
furrow passes completely through entire
length of the egg and bisects it into two equal
parts.
2. Holoblastic unequal cleavage: The cleavage
furrow passes completely through the egg Fig. Implantation 7 days after fertilization
but not through the centre.
3. Meroblastic or Discoidal cleavage: This type (iii) Blastulation: Formation of blastula from morula
of cleavage takes place in the macrolecithal is called blastulation. It is a hollow structure and
eggs. In such eggs the active cytoplasm is its cavity is called blastocoel. The blastula of man
confined to a small portion of egg. The and most of the mammals, is called blastocyst.
cleavage furrow therefore restricted only to Blastocoel is a fluid filled cavity.
this disc.
4. Superficial cleavage: This cleavage occurs
centrolecithal eggs. Here early division
occur in the surface layer of the egg. Zygote
Blastomeres
8 cell stage
2 cell stage 4 cell stage
(ii) Implantation: By the end of the morula stage. Zona pellucida Inner cell mass
Zona pellucida
The embryo reaches into cavity of uterus. By this starts
time, endometrium of uterus, becomes fully degenerating

prepare to receive the morula. On about 7th day of

fertilization it gets attached to the wall of uterus. Blastocoel
Morula Trophoderm
The blastocyst becomes embedded in the (16 celled) Blastulation Blastocyst (blastula)
endometrium of the uterus. This is called
implantation. During implantic embryo produces Fig. Cleavage, formation of morula and blastocyst
hCG, which plays an important role in Type of blastula: The type of blastula vary
implantation. After implantation, the uterine according to the egg type:
endometrium undergoes profound change. It is 1. Stereo blastula: The blastula is soild without
now called as decidua. blastocoel. e. g., sponges
2. Coeloblastula: The blastula with prominent
blastocoelic cavity.
 26

e. g., In all isolecithal and mesolecithal eggs. Events of fertilization: Fertilization is a physico -
3. Discoblastula: The blastula is formed as a chemical process. When sperms reach the uterus and
result of discoidal cleavage and has many fallopian tube, following important events take place.
layered disc of blastomeres over the 1. Arrival of sperms to ovum: For fertilization sperm
underlying yolk. e.g., Birds (Polylecithal and ova come to each other. Sperms are motile
egg). and reach the ovum with the help of tail
4. Superficial: The blastula is develops as a movement.
result of ruperficial cleavage. e. g., eggs of 2. Capacitation and contact: The changes in
insects. mammalian spermatozoon which make it capable
(iv) Gastrulation: The process of the formation of of fertilizing the egg have been called
gastrula from the blastula is called as gastrulation. capacitation. The secretion of female genital tract
It involves differentiation are movement of cells remove coating substance deposited on the
of blastocyst from their original place to the site surface of sperms particularly on acrosome. Thus
where they finally settle. During the formation of receptor sites on acrosome are exposed and
gastrula, the cells of inner cell mass get arranged sperms becomes active to penetrate the egg. It
in two layers. The upper layer forms ectoderm. takes about 5- 6 hours for capacitation.
Some cells also get separated and they form the
amnion.
Some cells on the surface of ectoderm accumulate Cells of corona
to form node like structure, called primitive Spermatozoa radiata
streak. The cells then moves downwards between
ectoderm and endoderm and form another layer,
called mesoderm. The embryo now has three Ovum
layers— ectoderm, mesoderm and endoderm.
Differentiated endodermal cells
(start delamination)
Zona Peri-vitelline space
Pellucida
Trophoderm
Fig. Human ovum, at the time of fertilization
3. Fertilizin-antifertilizin interaction: Ovum secretes
Growing a chemical named fertilizin composed of
endoderm
glycoprotein present in the surferce layer of the
Remaining cells of Amniogenic cells
inner cell mass (formed by trophoderm egg. While antifertilizin is another substance
become flattened Amniotic cavity present in surface layer of the cytoplasm of
Amnion
with fluid
Ectoderm spermatozoa. Sperm has a protein substance on
Endoderm its surface named anti-fertilizin (protein). Both
Yolk sac
Allantois
react like antigen antibody, as a result the sperm
get attached to ovum surface. It is called sperm
Amnion Primitive agglutination. The reaction is known as fertilizin-
streak
Formation of
antifertilizin reaction.
mesoderm
Yolk sac

Allantois
Chorion
Fig. Stages of gastrulation (formation of 3 germ layers) and
formation of foetal membranes
Q. 2. What is fertilization? Explain the events happen during
the fertilization in human and draw a labeled diagram
of ovum penetrating by sperm? (2011)
Ans. Fertilization: The fusion of male (sperm) and female
(ovum) gametes is called fertilization. Fertilization
takes place in fallopian tube (ampulla). A diploid
zygote is formed due to fertilization.
Fig. Cleavage and implantation of embryo
 27

4. Acrosome reaction and penetration: After the 1. Testes: These are the primary sex organs of
attachment of the sperm to the egg surface males, located outside the abdominal cavity in a
acrosome releases sperm lysins, e.g., pouch called scrotum. Testes are oval in shape,
hyaluronidase enzyme in mammals. The sperm with a length of 4-5 cm and width 2-3 cm. They
lysin digest the egg membranes to create a contain about 250 compartments called testicular
passage for sperm entry. A fertilization membrane lobules, containing highly coiled seminiferous
is formed in egg just after the entry of sperm. This tubules. Each seminiferous tubule is lined on its
membrane prevents polyspermic fertilization. inside by two types of cells.
5. Activation of ovum: Entry of sperm into ovum (i) Nurse cells or Sertoli cells: These cells
increased the permeability of plasma membrane provide nutrition to spermatozoa. They
for water, ethylene glycol, Phosphate and synthesise and secrete testosterone that
potassium and synthesis of cAMP is started. It controls spermatogenesis.
stimulate the secondary oocyte to complete (ii) Male germ cells: These cells undergo
second meiotic division. This produces a haploid meiosis to form spermatozoa.
mature ovum and a second polar body. 2. Accessory Glands
Female pronucleus and male pronucleus move toward (i) Prostate gland: It is alkaline secretion (pH
each other. Mixing up of the chromosomes of a sperm 7.4) helps in activation of sperms.
and ovum is known as karyogamy. The fertilized ovum (ii) Bulbourethral glands: These are also known
is now called zygote. as Cowper’s glands. Its viscous mucus, acts
Q. 3. Draw the diagram of oogenesis in human and compare as a lubricant for penis. It also neutralises
it with spermatogenesis. (2019) aciding of urine residue in urethra.
(iii) Seminal vesicle: It secretes mucus and
Ans.
watery alkaline fluid containing nutrients
Germ cell 2x
such as fructose, citric acid, inositol and
prostaglandins. It provides energy to
phase (Mitosis)
Multiplication

spermatozoa.
2x 2x
3. Accessory Ducts:
Oogonium
(i) Vasa efferentia: Number of tubules arising
2x 2x 2x 2x
from rete testis to conduct sperms to
epididymis are collectively called vasa
Fetal life

efferentia.
Growth
phase

(ii) Vasa deferentia: These are ducts arising from

Primary 2x
oocyte epididymis, ascending to the abdomen and
loops over urinary bladder.
childhood
puberty

(iii) Ejaculatory duct: The vas deferens when

Birth

pass over urinary bladder, receive a duct

Maturation

Secondary First polar from seminal vesicle, thus forming the

phase

oocyte x body
(at this stage
2nd meiotic
division (it occurs (In man and ejaculatory duct. It opens into urethra.
reproductive

ovulation
occurs)
after the fertilisation) many species,
M II in first
(iv) Rete testis: It comprises of anastomosing
Adult

network of tubules carrying sperms from

life

polar body does

not occur)
Mature seminiferous tubules to efferent ducts.
x
ovum (v) Epididymis: It serves as site for sperm
Oogenesis in human maturation and storage till their ejaculation.
Comparison between oogenesis and spermatogenesis: (vi) Urethra: It is called as urogenital duct as it
Please see the answer of Short answer type question-4. provides exit for urine from bladder as well
Q. 4. Describe human’s male reproductive system with the as semen from vasa deferentia.
help of labelled diagram. (2019) 4. External genitalia penis: It is male external
Ans. Male reproductive system: Male reproductive system genitalia comprised of vascular, spongy tissue
of human have following parts— that help in its erection to facilitate insemination.
It serves as copulatory organ to transmit sperms
into vagina of female during coitus.
 28

menstrual flow and for serving as a birth canal

during parturition.
C. Accessory glands contain a pair of Bartholin’s
gland occurs on each side of vaginal orifice.
These correspond to Cowper’s gland of the male
and secrete a clear and viscous fluid under sexual
excitement which serves as a lubrication during
copulation.
D. Mammary glands are paired structures, i. e.,
breast in females. Breast are rounded paired
structures located over the pectoral muscles on the
front wall of thorax.

Fig. Male reproductive system

Q. 5. Describe human female reproductive system with the
help of labelled diagram. (2019, 20)
Ans. Female reproductive system is located in pelvic
cavity. It consists of following organs.
A. Primary sex organs ovaries are primary sex
organs in women.
â Ovaries produce female gametes (ovum) and several
female hormones, i. e., ovarian hormones. The
Fig. Female reproductive system
broad ligament of uterus attaches ovaries by double-
layered fold of peritoneum called mesovarium. â The glandular tissue of each breast is divided into
â These are covered by cubical epithelium, i. e., 15-20 mammary lobes containing clusters of
germinal epithelium. These cubical epithelium mammary alveoli, which open into mammary
enclose ovarian stroma and it is divided into two tubules.
zones; peripheral cortex and inner medulla. â Each breast contains a nipple in its middle, which is
B. Secondary sex organs constitute following surrounded by circular and pigmented area called
organs. areola. Just under nipples, the lactiferous ducts
(i) Fallopian tubes (oviducts) are 10-12 cm long and widen to form lactiferous sinuses to store milk
consist of : during lactation.
(a) Infundibulum is broad and funnel-shaped E. External genitalia are collectively known as
with its motile and finger-like projections vulva that consists of following structures.
called fimbriae. (i) Mons pubis is the anterior most portion of
(b) Isthmus is short, narrow and thick-walled external genitalia which is cushion of fatty
portion that follows ampulla. tissue covered by skin and pubic hair.
(c) Ampulla is the widest and longest part of (ii) Clitoris is homologous to glans penis. It
Fallopian tube. contains erectile tissue and does not has any
(d) Uterine part passes through uterine wall and passage.
communicates with uterine cavity. (iii) Hymen it is a thin mucus membrane, which
(ii) Uterus is 7.5 cm long and 5 cm wide like an covers the vaginal opening either partly or
inverted pear in shape. It lies between urinary completely. It is often torn during first coitus.
bladder and rectum. It receives ovum from the Q. 6. Describe spermatogenesis in man and make a well
Fallopian tube and forms placenta for the labelled diagram of sperm. (2019)
development of foetus, cervix is narrow opening Ans. Spermatogenesis : Please See NCERT Question-6.
of uterus into vagina. Diagram of sperm : Short Answer Type Question-3.
(iii) Vagina is about 10 cm long and acts as receptacle Q. 7. What is gametogenesis? Explain the process of
for penis during copulation for allowing spermatogenesis in human with the help of labelled
diagram. (2020)
 29

Ans. Gametogenesis is the process of formation of haploid i. e., spermatogenesis in males and oogenesis in
gametes from the undifferentiated diploid germ cells in females.
the gonads for reproduction sexual. It is of two types, Spermatogenesis please see NCERT exercise
question-6.

NCERT Fully Solved Exercise

Q.1. Fill in the blanks : richly supplied with blood capillaries and nerve
(a) Humans reproduce ………………… tissues.
(asexually/sexually) The epithelium of these tubules is called germinal
(b) Humans are ………………… (oviparous, epithelium, which consists of mainly 3 types of cells—
viviparous, ovoviviparous) (a) Spermatogonia (follicular cells), (b) Interstitial
(c) Fertilisation is ………………… in humans cells (Leydig cells), and (c) Sertoli cells.
(external/internal) (a) Spermatogonia (follicular cells) : These are
(d) Male and female gametes are ………………… highly specialised cells, which undergo
(diploid/haploid) spermatogenesis to produce sperms (male
(e) Zygote is ………………… (diploid/haploid) gametes).
(f) The process of release of ovum from a mature (b) Interstitial cells (Leydig cells) : These are small
follicle is called ………………… . rounded cells, placed in small groups, scattered
(g) Ovulation is induced by a hormone called between seminiferous tubules. These cells
………………… . produce male hormones (androgens), such as
(h) The fusion of male and female gametes is called testosterone.
………………… . (c) Sertoli cells : These are large cells, present in the
(i) Fertilisation takes place in ………………… seminiferous tubules. These are also called nurse
(j) Zygote divides to form ………………… which is cells. These provide nutrition to the developing
implanted in uterus. spermatids and sperms.
(k) The structure which provides vascular connection Q.6 What is spermatogenesis? Briefly describe the process
between foetus and uterus is called of spermatogenesis. (2019)
………………… . Ans. The formation of sperms (male gametes) is called
Ans. (a) sexually (b) viviparous (c) internal spermatogenesis. This process takes place inside the
(d) haploid (e) diploid (f) ovulation testis. It involves three phases :
(g) LH (Luteinising hormone) (i) Multiplicative phase : In this phase the
(h) syngamy (fertilisation) primordial germ cells of germinal epithelium
(i) fallopian duct (oviduct) multiply and grow rapidly. After many divisions,
(j) blastocyst (k) placenta. these cells become sperm mother cells (or
Q.2 Draw a labelled diagram of male reproductive system. spermatogonia).
Ans. See Long answer type question-4. (ii) Growth phase : Now each spermatogonium
Q.3 Draw a labelled diagram of female reproductive absorbs a large amount of nutrition and become
system. larger in size. It is now referred to as primary
Ans. See Long answer type question-5. spermatocyte.
Q.4 Write two major functions each of testis and ovary. (iii) Maturation phase : In this phase, each primary
Ans. Major functions of testis and ovary are : spermatocyte undergoes meiosis I division to
Testis : (i) To form male gametes i.e., sperm. form two haploid cells, called secondary
(ii) To release male sex hormone testosterone. spermatocytes. These cells now follow meiosis II
Ovary : (i) To form female gamete i.e., ovum. (M-II) division. These division results in the
(ii) To release female sex hormones, estrogens and formation of round, haploid cells, called
progesterone. spermatids.
Q.5 Describe the structure of a seminiferous tubule. These spermatids are finally transformed to sperms by
Ans. Seminiferous tubules are highly coiled about 70 cm a process, called spermiogenesis. During this process
long (when uncoiled) tube like structures. These are the Golgi complex of the spermatid gives rise to the
acrosome that contains hyaluronidase. The
 30

mitochondria increase in number and form a

mitochondrial sheath in the middle piece. Sperm has a
motile tail.
Type of
division 2n Germinal epithelial cell
Daughter cells or
spermatogonium primordial germ cells
remains as a

Multiplication Phase
precursor Multiplication
stem cell 2 n Mitosis 2n (mitosis)

2n 2n 2n 2n (Spermatogonia)

2n 2n 2n 2n 2n 2n 2n 2n
Phases of Spermatogenesis

(Spermatogenesis)
Growth
Phase

(Growth)
2n Primary spermatocyte
(2n = 46 chromosomes) 46 (1st Maturation division) = Reduction
division (meiosis-II)
Each chromos- n n Secondary spermatocyte
Maturation

ome has two 23 23 (2nd Maturation division=

Phase

chromatids Equatorial
division (meiosis-II)
n n n n
23 23 23 23 Cytoplasmic bridge
Spermatozoa Spermatids
Spermatogenesis

n
n n n
Sperm

(n = 23 chro- (Spermatogenesis)
mosomes)

Fig. Different phases of spermatogenesis in human (male)

Q.7 Name the hormones involved in regulation of Ans. The liquid base of the semen is called seminal plasma.
spermatogenesis. It is 90 % of the total volume of the semen. (rest 10 %
Ans. Spermatogenesis starts at the age of puberty due to are the sperms). Seminal plasma contains (i) citrate,
significant increase in the amount of hypothalamic ascorbic acid, calcium (ii) acid phosphatase, (iii) and
hormone, called GnRH. This hormone stimulates fructose. The concentration of seminal plasma citrate
pituitary gland to release FSH and LH hormones. Both depends on the testosterone concentration and activity.
these hormones, are called gonadotropins as they Fructose, is the chief constituent of seminal plasma. It
stimulate and prepare testes to carry out is the principal fuel of the spermatozoa while they are
spermatogenesis. FSH directly increases the growth of in the female genital tract. The seminal plasma is also
spermatogonia and stimulate their divisions. LH (also rich in prostaglandin (local hormones), various
called ICSH) stimulates interstitial cells to release proteins (such as fibrinogen).
testosterone. Testosterone finally stimulates and Q.11 What are the major functions of male accessory ducts
controls the spermatogenesis. and glands?
Q.8 Define spermiogenesis and spermiation. Ans. The major functions of male accessory ducts and
Ans. The transformation (metamorphosis) of spermatids glands :
into sperms (spermatozoa), is called spermiogenesis (a) Vasa efferentia : To convey sperms to epididymis.
(or spermateliosis). After spermiogenesis, the sperm (b) Epididymis: To mature the spermatozoa and make
heads become embedded in the sertoli cells (to obtain them motile. It also conveys sperms to vas
nutrition) and finally get released from the deferens.
seminiferous tubules. This release is called (c) Vas deferens : To convey sperms to urethra.
spermiation. (d) Prostate gland : To secrete a fluid, which mingles
Q.9 Draw a labelled diagram of sperm. with the secretion of the testes and accounts for
Ans. See short answer type Q.no. 3 about 20% of the volume of semen. This secretion
Q.10 What are the major components of seminal plasma? is acidic in nature.
 31

(e) Seminal vesicle : Its secretion contains citrate, Ans. (a) Corpus luteum : To secrete progesterone.
fructose, inositol and hyaluronidase (an enzyme (b) Endometrium : It is the innermost layer of the
that helps in fertilisation). Besides it also contains uterine wall. It helps in the implantation of
prostaglandins (local hormones). Its secretion blastocyst and formation of placenta.
forms about 70 % of the semen. (c) Acrosome: It contains hyaluronidase enzyme,
(f) Cowper’s glands (bulbo-urethral glands) : To which dissolves the wall of ovum and help in
secrete mucus, which lubricates the passage of fertilisation.
urethra for the easy ejaculation of semen.
(d) Sperm tail : It is flagellum that helps the sperm to
Q.12 What is oogenesis? Give a brief account of oogenesis.
move.
(2019)
Ans. The formation of female gamete (ovum) is called (e) Fimbriae : These are finger like ends of the
oogenesis. It is long and discontinuous process that fallopian tubes, which serve to receive the ovum
occurs in ovary. It also involved following three after ovulation.
phases: Q.16 Identify True/False statements. Correct each false
(i) Multiplicative phase : In this phase the statement to make it true.
primordial germ cells of germinal epithelium or (a) Androgens are produced by Sertoli cells.
ovary multiply and grow rapidly. This occurs in (True/False)
the intra-uterine life (before birth). After many (b) Spermatozoa get nutrition from Sertoli cells.
divisions, these cells become oogonia. (True/False)
(ii) Growth phase : Now each oogonia absorbs a (c) Leydig cells are found in ovary. (True/False)
large amount of nutrition and become larger in (d) Leydig cells synthesise androgens. (True/False)
size. It is now referred to as primary oocyte. (e) Oogenesis takes place in corpus luteum.
(iii) Maturation phase : It occurs after puberty. In the (True/False)
beginning of each menstrual cycle, a primary (f) Menstrual cycle ceases during pregnancy.
oocyte starts development. It undergoes meiotic-I (True/False)
division, forming a secondary oocyte (haploid) (g) Presence or absence of hymen is not a reliable
and a polar body. indicator of virginity or sexual experience.
Now ovulation takes place. The secondary oocyte (True/False)
follows the second meiotic division (M II), only if it is Ans. (a) False (b) True (c) False
fertilised by a sperm. Finally, mature haploid ovum is (d) True (e) False (f) True
formed. Simultaneously second polar body is extruded. (g) True
Both primary and secondary polar bodies are Q.17 What is menstrual cycle? Which hormones regulate
degenerated. menstrual cycle? (2019, 20)
Q.13 Draw a labelled diagram of a section through ovary. Ans. It is the characteristic 28 day cycle in fertile human
Ans. See short answer type Q.no. 2 females. It involves bleeding phase, proliferative phase
Q.14 Draw a labelled diagram of a Graafian follicle? and secretion phase.
Ans. (i) Bleeding phase — It occurs for first 4-5 days. It
involves the dischages of blood and debris
through vagina.
(ii) Proliferative phase — By 5th day, bleeding is
usually stopped and ovary starts forming a fresh
Graafian follicle. By 14th day, the growth of
Graafian follicle is completed and on 14th day,
ovulation occurs.
(iii) Secretory phase — The period between 14th day
to 28th day is called secretory period, as it
Fig. A mature Graafian follicle
involves the profuse secretion of mucus from
uterine endometrium.
Q.15 Name the functions of the following: Hormonal regulation : The proliferative phase is
(a) Corpus luteum (b) Endometrium controlled and regulated by FSH of pituitary and the
(c) Acrosome (d) Sperm tail estrogen secreted by the ovary. On the other hand, the
(e) Fimbriae
 32

secretory phase is maintained by the LH of pituitary This clearly suggests that, there is no role of woman in
and progesterone, by ovary (Corpus luteum). sex determination and therefore she should not be
Q.18 What is parturition? Which hormones are involved in blamed.
induction of parturition? Q.20 How many eggs are released by a human ovary in a
Ans. The coming out of the baby from mother’s body after month? How many eggs do you think would have been
completion of pregnancy period (i.e., birth) is called released if the mother gave birth to identical twins?
parturition. Oxytocin is the principal hormone that Would your answer change if the twins born were
creates labour pains and help in the parturition process. fraternal?
Q.19 In our society the women are often blamed for giving Ans. Only one egg (ovum) is released by a human ovary in a
birth to daughters. Can you explain why this is not month. In case of identical twins, female would have
correct? been produced only one egg. After first division in the
Ans. This is completely incorrect. This is because, the sex is zygote, the two cells behave as separate zygotes and
determined by the nature of the sperm, not of ovum. give rise two identical twins. But in case of fraternal
Male produces two types of sperm — X type and Y twins, two eggs are produced.
type. But female produces only X type of ovum.
If X sperm of male and ovum of female get fertilised, a
female baby would be born. But if Y type sperm of ccc
male fertilises the ovum, a male baby would be born.
 33

Chapter

4 REPRODUCTIVE HEALTH

² Contraceptive Devices : Contraceptive devices are the ² Medical Termination of Pregnancy : Medical Termination
means which aim to prevent sexual intercourse from causing of Pregnancy (MTP) is also called induced abortion. It is the
pregnancy, i.e., preventing the meeting of sperm and ovum. An medical way of getting rid of unwanted pregnancy. It is a
ideal contraceptive device should be user friendly, easily banned process in India except for the cases of
available, effective and reversible with no or least side effects. abnormal/complicated pregnancies.
² Intra-Uterine Contraceptive Devices (IUCDs) : The ² Sexually Transmitted Diseases : Sexually transmitted
intra-uterine contraceptive devices are small plastic and copper diseases (also called STDs) are the infections/diseases, which
devices, which are fitted into the uterus. These are designed to can be transferred from one person to another through sexual
prevent the sperm meeting the egg, and may also make the egg intercourse. Important sexually transmitted diseases are —
move down the fallopian tube more slowly and stop an egg AIDS (HIV infection), Syphilis, Gonorrhea, Hepatitis-B,
settling in the uterus (if fertilised). trichomoniasis, genital warts, chlamydiasis, genital herpes,
² Emergency Contraceptive : This is used to prevent urithritis etc.
pregnancy after unprotected sexual intercourse (sex without ² Infertility : Infertility is the inability to naturally conceive a
any method of birth control or with a birth control method that child in spite of long term unprotected sex or to carry a
failed or was not used properly. It is a two tablet treatment, pregnancy to full term.
taken within 72 hours of unprotected sex. ² In Vitro Fertilization (IVF) : In infertile couples, where
² Sterilisation (Sergical Method) : This is a surgical method women have blocked or absent fallopian tubes, or where men
to permanently prevent fertilisation. It is therefore only have low sperm counts, in vitro fertilization (IVF) offers a
recommended for people who are sure they do not want to have chance at parenthood to couples who until recently would have
any more children. had no hope of having a “biologically related” child.
² Vasectomy : It is a surgical contraceptive measure for men, ² In IVF, eggs are surgically removed from the ovary and mixed
which involves cutting or tying the tubes (vas deferens) which with sperm outside the body in a petri dish )(‘‘in vitro’’ is Latin
carry sperm from the testicles to the penis. As a result the for ‘‘in glass’’). After about 40 hours, the eggs are examined to
ejaculated semen does not contain sperms. see if they have become fertilized by the sperm and are dividing
² Tubectomy : It is a surgical contraceptive measure for women, into cells. These fertilized eggs (embryos) are then placed in the
in which, both fallopian tubes (oviducts) are cut, tied or women’s uterus.
blocked, often through keyhole surgery. As a result the ovum
can not meet the sperms.

Multiple Choice Questions 1 Mark

Q.1. World health day is celebrated every year on: (d) Treponema pollidum
(a) 7 th March (b) 7 th April Q.3. Emergency contraceptives contain:
(c) 7 th July (d) 7 th May (a) Progesterone only
Q.2. Gonorrhea is caused by: (b) Progestogens and estrogen
(a) Neisseria gonorrhoeae (c) Progestogens and testosterone
(b) Chlamydia trachomatis (d) Estrogens and androgen
(c) Mycoplasma hominis
 34

Q.4. Hormone based IUDs make the: (c) Sex of the toetus (d) Down syndrome
(a) Sperm immovable Q.7. Syphilis is caused by:
(b) Ovum resistant to sperms (a) Neisseria gonorrhoeae
(c) Uterine wall unsuitable for implantation (b) Chlamydia trachomatis
(d) All of the above (c) Mycoplasma hominis
Q.5. Assisted reproductive technology. IVF involves (d) Treponema pallidum
transfer of: Q.8. Presence of which one of the following substances in
(a) Ovum into the fallopian tube amniotic fluid is responsible for determination of sex
(b) Zygote into the fallopian tube of embryo? (2015)
(c) Zygote into the uterus (a) Barr bodies (b) Sex chromosomes
(d) Embryo with 16 blastomeres into the fallopian (c) Chiasmata (d) Antigen
tube Q.9. Which of the following is related to male? (2020)
Q.6. Which of the following can not be detected in (a) Vasectomy (b) Pills
developing foetus by amniocentesis? (c) Tubectomy (d) None of these
(a) Jaundice (b) Klinefelter syndrome

Answers
1. (b) 2. (a) 3. (b) 4. (c) 5. (b) 6. (a) 7. (d) 8. (b) 9. (a)

Very Short Answer Type Questions 1 Mark

Q. 1. Define a reproductive healthy society? Ans. It is a surgical method to block gamete transport and
Ans. A society with people having physically and there by preventing conception.
functionally normal reproductive organs and normal Q. 5. What is meant by artificial insemination?
emotional and behavioral interactions among them in Ans. It is a method by which semen collected from the
all sex- related aspects might be called reproductively husbands or a healthy donor is artificially introduced
healthy. either into the vagina or into the uterus of the female.
Q. 2. Name any two surgical method of contraception? Q.6. Name two sexually transmitted diseases caused by
Or What are the permanent methods of family bacteria?
planning? (2020) Ans. Syphilis and gonorrhoea.
Ans. Tubectomy (in females) and vasectomy (in males). Q.7. What do you mean by external fertilization? Give an
Q. 3. Name some barrier method of contraception designed example. (2019)
for females? Ans. External fertilization is a mode of reproduction in
Ans. Diaphragms cervical caps and vaults are some of the which a male sperm fertilises with egg outside of the
barrier methods used by females. female body.
Q. 4. What is sterilization?

Short Answer Type Questions 2 & 3 Marks

Q.1. Name any three incurable sexually transmitted diseases Bacterial: Gonorrhoea (Neisseria gonorrhoeae),
and their causative organisms? Syphilis (Treponema pallidum).
Ans. (i) AIDS—Human immunodeficiency virus Viral: Herpes, AIDS, Hepatitis B, Genital warts.
(ii) Genital warts—Human papilloma virus Protozoan: Vaginal trichomoniasis:
(iii) Herpes—Herpes simplex virus Trichomonas vaginals
Q.2. What do you mean by STDs? Q.3. What is infertility? Mention any there causes of
Ans. Sexually transmitted diseases or venereal diseases are infertility in men and women?
the infections/diseases, which can be transferred from Ans. Infertility: The incapability to produce children
one person to another through sexual intercourse. inspite of unprotected sexual intercourse is called
These infections may be bacterial, viral and protozoan infertility. A large number of couples all over the
etc. world including India are infertile, i. e., they are unable
 35

to produce children. Infertility is going at an alarming uterus by a doctor. It is designed to prevent the sperm
pace, cause of infertility in men: meeting the egg and may also make the egg move down
1. Physical retardation of sex organs. the fallopian tube more slowly and stop an egg setting
2. Congenital diseases. in the uterus.
3. Dry use. These intra uterine devices are presently available as
The most common male infertility factors include a the non- medicated IUDs (Lippes loop) Copper
zoospermia and oligospermia. releasing IUDs (CuT, Cu7, multi load 375, Para gard,
Cause of infertility in women: T-care) and the hormone releasing IUDs
The most common female infertility factor is an (Progestosert, LNG-20, PVR).
ovulation disorder. Other causes of female infertility IUCDs increase phagocytosis of sperms and the copper
include, blocked fallopian tubes. reduces sperm motility. The hormone releasing IUDs,
Q. 4. What do you mean by contraception? Name the natural make the uterus unsuitable for implantation.
methods of contraception? Q.6. Write short note on MTP?
Ans. Contraception: Birth control, also known as Ans. MTP: Medical termination of pregnancy is also called
contraception is designed allow people to attain their induced abortion. It is the medical way of getting rid of
desired number of children and determine the spacing unwanted pregnancy. Government of India legalized
of pregnancies. MTP in 1971 through Medical Termination of
Different contraceptive methods are broadly Pregnancy Act No. 34 of 1971 with some strict
categorized into two main types : conditions to avoid its misuse.
(i) Temporary or spacing method. MTPs are considered relatively safe during the first
(ii) Terminal or permanent methods. trimester, i.e., upto 12 weeks of pregnancy.
Temporary method are used to postpone or to space Complications of MTP: MTP is a procedure that is
births. These can be grouped into following sub carried and under anaesthesia and increases the risk for
categories: the procedure. Patients can have lot of bleeding during
(a) Natural methods (b) Barrier methods and after the procedure. There are high chances of
(c) Intra uterine contraceptive devices patient having recurrent abortions.
(d) Chemical methods Q.7. What is amniocentesis? Why has the government
(e) Oral contraceptive pills imposed a statutory ban in spite of its importance in the
(f) Morning after pills medical field?
Natural methods: This involves the strategies where Ans. Amniocentesis: Amniotic fluid test (AFT) is a medical
no external is used, i.e., chances of pregnancy are procedure used in prenatal diagnosis of chromosomal
avoided in natural way. It involves following methods. abnormalities and fetal infections, and also for sex
1. Periodic abstinence: This is a modified from of determination, in which a small amount of amniotic
abstinence also called the fertility awareness' or fluid, which contains fetal tissues, is sampled from the
symptom-thermal method. The idea is to retrain amniotic sac surrounding a developing foetus, and then
from intercourse during the woman's heat period, the fetal DNA is examined for genetic abnormalities.
starting a few days before ovulation and ending a Amniocentesis is performed when a woman is between
few days after, i.e., 10th to 17th of menstrual 14 and 16 weeks gestation.
cycle. Government ban: Women who choose to have this
2. Withdrawal method: It involves the withdrawing test are primarily those at increased risk for genetic and
the penis before ejaculation. It is not a reliable chromosomal problems. This process can be used for
prenatal sex determination. So amniocentesis is
method before some sperms can leak out of the
misused to determine the sex of the unborn child.
penis before ejaculation. Frequently it the foetus is found to be female, it is
3. Lactational amenorrhoea method (LAM): There follow by MTP. So, to discourage such practice our
is no menstrual cycle and therefore ovulation does government has imposed a ban on this process.
not occur during intense lactation following Q.8. Describe sterilization (surgical method) in males and
parturition. females?
Q.5. Write short notes of Intra uterine contraceptive devices Or What is the permanent or terminal methods of
(IUDs or IUCDs)? contraception?
Ans. IUDs or IUCDs: The intra-uterine contraceptive Or Comment of vasectomy and tubectomy?
device or coil commonly called copper-T or cut is Ans. Sterilization: It is a surgical method to permanently
small plastic and copper device. Which is fitted into the prevent fertilization. It is therefore only recommended
 36

for people who are sure they do not want to have any Ans. Causes of population explosion : NCERT ques. 5. and
more children. Sterilization can achieved either by Measure to control population : Please see Long
prohibiting the transport of sperm from passage an egg answer type question-2.
from a woman’s ovaries to her oviduct Q.12. What do you mean by sexually transmitted disease?
(1) Vasectomy: Men are sterilized in a procedure Mention suitable measures for their prevention. (2019)
called a vasectomy. This is a minor operation Ans. See Long answer type question-3.
usually performed under local anaesthetic. It Q.13. Define assisted reproductive technique and give an
involves cutting or tying the vas deferens which account of IVF. (2019)
carry sperm. Ans. See Long answer type question-1.
Q.14. Write short note on IVF technique. (2019)
Ans. IVF technique : Please see Long answer type
question-1.
Vas deferens Q.15. Explain the process of in vitro fertilization (IVF) in
tied and cut
brief. (2020)
Ampulla of Ans. Please see Long answer type question-1.
vas deferens
Q.16. Family planning is in favour of Nation, why? (2020)
Epididymis Ans. Today the demographic dividend is in India’s favour
Testis
and family planning can and should be used to leverage
it. Longer lives and smaller families lead to more
Corona
working age people supporting fewer dependents. This
Glans penis
reduces cost and increases the country’s wealth,
Fig. Vasectomy (In human male) economic growth and productivity of the people.
Fallopian tubes Investing in family planning is the most intelligent step
tied and cut that a nation like India can take to improve the over all
socio-economic fabric of the society and reap high
returns on investments and drive the country’s growth.
Q.17. Describe in brief the ‘Barrier methods’ used by male to
enhance contraceptive capacity. (2020)
Ans. Barrier Methods : These methods are used to prevent
Ovary the sperms to reach in fallopian tubes. The short
Cervix
description of these methods are as following—
(i) Condom : These are made of thin rubber or latex
sheath. These are used to cover the penis in males.
Vagina
These are used just before the coitus so that
Fig. Tubectomy (In human female) ejaculated semen would not enter into the female
reproductive tract.
(2) Tubectomy: Surgical sterilization procedure of
(ii) Coitus Interruptus : In this method, male
female is called tubectomy or tubal-ligation. In
withdraw his penis from female’s vagina just
this method, both fallopian tubes (oviducts) are
before ejaculation.
cut, tied or blocked, so the sperm cannot reach to
(iii) Vasectomy : The procedure by which men are
ovulated oocytes. Tubal-ligation is not associated
sterilized is called vasectomy. This is a minor
with any health risk outside of those associated
operation usually performed under local
with surgery of the abdominal cavity.
anaesthetic. It involves cutting or tying the vas
Q.9. Write short note on test tube baby. (2009, 14)
deferens which carry sperm.
Ans. See Long answer type question no.-1.
Q.18. Describe different methods of Assisted Reproductive
Q.10. Write a brief note on family planning. (2014)
Technologies (ART). (2020)
Ans. See Long answer type question no.-2.
Ans. Please see Long answer type question-1.
Q.11. What are the main causes of population explosion?
Describe birth control measures. (2019)
 37

Long Answer Type Questions 5 Marks

Q.1. What are the Assisted Reproductive Techniques placed in one of the fallopian tubes, along with the
practiced to help infertile couples? Describe any three man’s sperm. This allows fertilization to take place
techniques? inside the woman body.
Or Explain IVF and FET. What are the conditions in Q.2. How can increase in population be controlled?
which these methods are advised? Describe in brief various scientific method of family
Ans. Assisted Reproductive techniques: The term ART is planning. (2011)
used in different contexts but should cover induction of Or What is the need of family planning? Describe
ovulation, sperm preparation, intrauterine various measures of birth control. (2016)
insemination, IVF,ICSI and genetic testing and Or Explain the necessity of family planning in India,
manipulation. and its methods. (2020)
Thus ART is useful technique, meant for the treatment Ans. Measure to control population :
of infertility. The Assisted Reproductive Technique Steps to control population growth are :
practiced to help infertile couples are as follows : (i) Statutory raising of marriageable age of boys to
1. In vitro fertilization (IVF): IVF is the most common 21 years and 18 years in case of girls.
ART technique. The object of IVF is to add sperm to (ii) By giving incentives to the couples with small
egg in the laboratory. Where the normal pathway via families.
the fallopian tubes is damaged or absent. (iii) Motivate smaller families by using various
Hence this process is also called test tube baby contraceptive methods.
technique. Need of family planning are as follows :
The first test tube baby Louise Joy Brown was born on (i) Preventing pregnancy-related health risks in
July 25, 1978 in England with the help of Dr. Robert women : Family planning allows spacing of
Edwards and Dr. Patrick Steptoe. IVF offers a pregnancies and can delay pregnancies in young
chance at parenthood to couples who until recently women at increased risk of health problems and
would have no hope of having a “biologically related death from early childbearing. It prevents
child.” unintended pregnancies, including those of older
In IVF, eggs are surgically removed from the ovary and women who face increased risks related to
mixed with sperm outside the body in a Petridish or test pregnancy.
tube. After about 40 hours, the eggs are examined to (ii) Reducing infant mortality : Family planning can
see it they have became fertilized by the sperm and are prevent closely spaced and ill-timed pregnancies
dividing into cells. Ideally one embryo is transferred and births, which contribute to some of the
into the mother’s uterus by means of a thin plastic tube. world’s highest infant mortality rates.
2. Embryo Freezing and Replacement (Transfer) (EFT): (iii) Empowering people and enhancing education:
In this method embryos can be stored for years without Having smaller families allows parents to invest
any apparent defeats occurring. These can be thawed more in each child. Children with fewer siblings
and replaced in normal cycles greatly simplifying the tend to stay in school longer than those with many
patients treatment cycle and costs. At this time it would siblings.
appear that the pregnancy rate from frozen embryos is (iv) Helping to prevent HIV/AIDS : Family
lower than that from fresh embryos. planning reduces the risk of unintended
3. ICSI (Intracytoplasmic sperm injection): In this pregnancies among women living with HIV
technique, a single sperm is injected into an egg, the resulting in fewer infected babies and orphans.
fertilized egg is then placed in the woman’s uterus as in (v) Reducing adolescent higher pregnancies :
IVF. Thus the couple requires very few sperm for this Babies born to adolescents have higher rates of
type of therapy. neo-natal mortality.
4 Zygote intrafallopian transfer (ZIFT): In this (vi) Slowing population growth : Family planning is
technique, eggs are removed from the woman, key to slowing unsustainable population growth
fertilized and then placed in the woman’s fallopian and the resulting negative impacts on the
tubes rather than the uterus. economy, environment, and national and regional
5. Gamete Intrafallopian transfer (GIFT): In this development efforts.
technique, egg are removed from the woman, and
38

Birth control or contraception : The population (v) Intra Uterine Devices (IUDs) : These devices
growth can be controlled only by adopting suitable contain either copper or progesterone, and are
contraceptive methods : inserted by doctors into the uterus through vagina.
(i) Natural/traditional methods : These methods They are a form of long reversible contraceptive
are based on the principle of avoiding chances of method. These may be categorised as :
meeting sperms and eggs. (a) Copper releasing IUDs : Cu-T, Cu-7
(a) Coitus interruptus or withdrawal : In this Multiload-375 and Paragard are some of the
method, the male partner withdraws his penis Cu-releasing IUDs.
from the vagina just before ejaculation so as (b) Hormones Releasing IUDs : Progestasert,
to avoid insemination. LNG-20, Mirena are the well known
(b) Periodic abstinence : It is a method in which hormone releasing IUDs.
couples avoid coitus (intercourse) from day (c) Non-medicated IUDs, e. g., Lippes loop.
10-17 of the menstrual cycle, because (vi) Injectables and implants hormone injections :
ovulation can occur mostly during this time, These are progesterone-derivative injections,
(it is caved the fertile period). given every three months, that releases a hormone
(c) Lactational amenorrhea : It refers to the slowly and prevent ovulation. They are
stoppage of menstruation during the period convenient, highly effective with no side effects.
of lactation following parturition. Implants are the new method of contraception,
Because ovulation does not occur in this
which is subcutaneous implantation of synthetic
period, the chances of conception are
progesterone. Though, these act similarity to oral
minimum or nil.
contraceptives by blocking ovulation and
(ii) Barrier methods : These methods prevent
thickening the cervical mucus, to prevent sperm
sperms and ovum, from physically meeting in
transport, their effective periods are longer. One
order to prevent fertilisation. These methods are
implant is effective for about five years.
available for both males and females. These are as
(vii) Emergency contraceptives (Morning after pills):
follows :
Administration of progestogens or progestogen-
(a) Cervical caps, diaphragms and vaults :
These are also made of rubber and are oestrogen combinations or IUDs within 72 hours
inserted into the female reproductive tract to of coitus have been very effective as emergency
cover the cervix during intercourse. These contraceptives as they could be used to avoid
are reusable. possible pregnancy due to rape or casual
(b) Condoms : These are made of thin rubber or unprotected intercourse. Their side effects are
latex sheath. Used to cover the penis in males menstrual irregulation, vomiting, etc., e. g., i-pill,
and vagina and cervix in females. These are Pill-72, Unwanted-72.
used just before coitus so that ejaculated (viii) Surgical methods : Such methods block the
semen would not enter female reproductive transport of gametes thereby prevent conception,
tract. i. e., vasectomy and tubectomy.
(iii) Chemical methods : Spermicides come in the Q.3. STDs are a threat to reproductive health. Describe any
form of creams, jellies and foams and are usually two such diseases and their preventive measures.
used along with the above stated barriers to Ans. Sexually Transmitted Diseases (STDs) : These are
increase their contraceptive efficiency. diseases that are mainly passed from one person to
These are inserted in the vagina before another during sexual intercourse. They are also
intercourse. These contain spermicides (kill known as Venereal Diseases (VDs) or Reproductive
spermatozoa) such as lactic acid, citric acid, boric Tract Infections (RTIs). These can be prevented by
acid, zinc sulphate and potassium permanganate. avoiding unprotected sexual intercourse. Genital
(iv) Oral contraceptives : These are the preparations herpes, syphilis, gonorrhoea, chlamydiasis, genital
of hormones either progestogens or progesterone- warts, hepatitis-B and infection of HIV leading to
oestrogen combinations in the form of pills, used AIDS are some common STDs. STDs are a major
by the females. threat to a healthy society. These diseases are reported
They alter or inhibit ovulation and fertilisation to be high among individuals in the age group of 15-24
and also modify the quality of cervical mucus to years.
prevent or retard the entry of sperms. Most Except for heptatitis-B, genital herpes and HIV
common examples are ‘Mala D’ and ‘Saheli’. infections, all other diseases are completely curable, if
 39

detected early and treated properly. The early (ii) Decline in death rate.
symptoms of STDs are minor and include itching, fluid (iii) Increase in the young, reproductive age
discharge, slight pain, swellings, etc., in the genital population.
region. Infected females may often be asymptomatic (iv) Continuous increase in the birth rate.
and hence, may remain undetected for long. STDs like (v) Poverty and illiteracy.
Hepatitis-B and HIV can also be transmitted by the (vi) Social stigmas about girl child and desire to have
following : boy child.
(i) Sharing of contaminated injection needles, Steps to control population growth are :
surgical instruments, etc., with infected persons. (i) Statutory raising of marriageable age of girls to 18
(ii) Transfusion of blood. years and 21 years in case of boys.
(iii) From infected mother to foetus. (ii) Motivate couples to have smaller families by
Preventive measures for STDs : One should not panic using various contraceptive methods.
because prevention from STDs is possible and one (iii) By giving incentives to the couples with small families.
could be free of these infections, by following these Consequences of Overpopulation :
simple principles as given below : Overpopulation has lead to various serious problems.
(i) Always use condoms during coitus. Some of these are given below as :
(ii) Avoid sex with unknown/multiple partners. (i) Unemployment : Overgrowing population is a
(iii) Awareness about STDs. main and the foremost reason for unemployment
(iv) Use sterilised needles and syringes. as number of people will increase, the job need
(v) In case of doubt, consult a doctor as early as will also increase.
possible for early detection and get completely Therefore, more number of people will remain
treated if diagnosed with disease. unemployed, if sufficient number of jobs are not
Q.4. Write an essay on population explosion and control. available.
(2019, 20) (ii) Food Supply : If the population keeps on
Ans. Population Explosion : Population represents the total increasing and the production of food will not
number of individuals of a species living in an area. increase. This will lead to shortage of food.
Increased health facilities along with better living (iii) Poverty : Family becomes naturally poor if there
conditions had an explosive impact on the growth of are more persons in it and the income is less.
population. A rapid increase in population over a Therefore, poverty increases with the increase in
relatively short period is called population explosion. every child in the family.
The world population, which was around 2 billion in (iv) Education : It is also one of the reasons as
1900 rocketed to about 6 billion in 2000. government tend to face difficulties in providing
In India too, we observed a similar growth pattern. Some education to all.
major reasons for population growth are as follows : Measure to control population : Please see the ans
(i) Ignorance and complete lack of awareness about the of Long answer type question-2.
ill-effect of increasing especially in rural regions.

NCERT Fully Solved Exercise

Q.1 What do you think is the significance of reproductive Ans. Two important aspects of reproductive health which
health in a society? need to be given special attention in the present
Ans. Reproduction is a process of bringing a new offspring scenario are:
in this world. So, reproductive health is significant to (a) Knowledge to young boys and girls so as to
give birth to healthy and fit offspring. It is important for discourage them from believing in myths and
all age groups especially young boys and girls of having misconception about sex related aspects.
reproductive age. Knowledge of reproductive health is (b) Knowledge of family planning to persons of
essential to boys and girls of pubertal age. So, that they reproductive age groups, so that they keep family
can understand the meanings of changes that take place size small and have sound reproductive health.
in their body during pubertal age. Q.3 Is sex education necessary in schools? Why?
Q.2 Suggest the aspects of reproductive health which need Ans. Yes. Sex education is essential in school. This is
to be given special attention in the present scenario. because, children attain their pubertal age during their
40

schooling. Puberty brings drastic changes in the Ans. Most infertility cases (85 to 90%) are treated with
physical and mental design of the body. If children are conventional therapies, such as drug treatment or
aware of such changes they can be prevented from surgical repair of reproductive organs. Common lines
believing in myths and having misconception about of treatment are :
sex related aspects. Fertility medication which stimulates the ovaries to
Q.4 Do you think that reproductive health in our country “ripen” and release eggs (e.g. clomifene citrate, which
has improved in the past 50 years? If yes, mention stimulates ovulation). Assisted reproductive
some such areas of improvement. techniques are suggested to assist infertile couples.
Ans. Yes. The reproductive health in our country has Please see the answer of long answer type question-1.
improved in the past 50 years. People are now well Q.10 What are the measures one has to take to prevent from
aware about the benefits of keeping their family size contracting STDs?
small. We now have widespread availability of means Ans. Two important measures, one has to take to prevent
of family planning. People are now more cautious from contracting STDs are :
about sex related diseases. However, in many parts of (a) Be loyal to one partner and avoid multiple sexual
the country, female infanticide is still continued. practices.
Diseases like AIDS are increasing. (b) Use barrier devices like condom.
Q.5 What are the suggested reasons for population Q.11 State True/False with explanation :
explosion? (a) Abortions could happen spontaneously too.
Ans. Some important reasons for population explosion are : (b) Infertility is defined as the inability to produce a
(a) Illiteracy. viable offspring and is always due to
(b) More hand more income thinking. abnormalities/defects in the female partner.
(c) Lack of availability of contraceptives. (c) Complete lactation could help as a natural method
of contraception.
(d) Decrease in death rate, maternal mortality rate
(d) Creating awareness about sex related aspects is an
(MMR) and Infant mortality rate (IMR). effective method to improve reproductive health
Q.6 Is the use of contraceptives justified? Give reasons. of the people.
Ans. Yes. The use of contraceptives is fully justified as it Ans. (a) True. Pregnancy is a hormonally controlled
gives encouragement to safer sexual practices. It is also process. So, any change in body’s hormonal
helpful in checking sexually transmitted diseases and environment, especially low level of
also helps in keeping the family size small. progesterone, can lead to abortion.
Q.7 Removal of gonads cannot be considered as a (b) False. Infertility may also be due to
contraceptive option. Why? abnormalities/defects in the male partner.
Ans. Gonads are important body organs, which not only (c) True. During lactation, menstruation does not
produce gametes but also produce sex hormones. Sex occur.
hormones are very important and they are responsible (d) True.
for onset of puberty and all secondary sexual features. Q.12 Correct the following statements :
So, removal of gonads would make the individual (a) Surgical methods of contraception prevent
completely sterile and he/she would have poorly gamete formation.
developed sex organs. So, removal of gonads cannot be (b) All sexually transmitted diseases are completely
considered as a contraceptive option. curable.
Q.8 Amniocentesis for sex determination is banned in our (c) Oral pills are very popular contraceptives among
country. Is this ban necessary? Comment. the rural women.
Ans. Yes. A ban on amniocentesis is necessary because this (d) In E.T. techniques, embryos are always
practice is being misused in the country. By this transferred into the uterus.
process, the sex of the foetus can be identified. In the Ans. (a) Surgical methods of contraception prevent
want of male baby, many persons go for abortion of gamete fusion.
female baby (female infanticide). So, to discourage (b) Most of the sexually transmitted diseases are
such practices, our Government has imposed a ban on curable but some like AIDS are not.
this process. (c) Oral pills are not very popular contraceptives
Q.9 Suggest some methods to assist infertile couples to among the rural women.
have children. (2020) (d) In Embryo transfer techniques, embryos are
always implanted into the uterus.
ccc
 41

Chapter

5
Unit-2 : Genetics and
Evolution PRINCIPLES OF
INHERITANCE AND
VARIATIONS

² Gene: These are the specific portions of DNA (Genetic ² Test Cross: A test cross is a back cross, which involves the
material), which contains information for the formation of a cross between F1 offspring with homozygous recessive (double
protein / polypeptide chain or perform a particular work. Genes recessive) parent. The test cross is used to determine the
are the units of heredity. homozygous or heterozygous nature of the F1 offspring.
² Chromosomes: These are thread like structures, visible only ² Linkage: The genes which are present on the same
in division phase. These represent the condensed form of chromosomes remain together as a block. When chromosome is
chromatin (DNA + histone proteins). Chromosomes are the transfer to the next generation, they are also transferred
vehicles of heredity. together. Therefore genes, which are found on the same
² Homologous Chromosomes: In a diploid cell, all chromosome, have tendency to remain together during the
chromosomes are present in the form of pairs. Each pair has two course of inheritance. This tendency of the genes to remain
morphologically similar kinds of chromosomes. These two together is called linkage.
chromosomes of a pair are called homologous chromosomes. ² Crossing Over: Crossing over can be defined as the process,
² Alleles: The genes, which govern the allelomorphic characters, which involves the exchange of chromosomal, parts between
are called alleles. non-sister chromatids of a homologous pair of chromosomes
² Genotype and Phenotype: The genetic configuration of an (bivalent) during prophase I of meiotic cell division. Crossing
organism (in relation to the inheritance of characters) is called over results in the rearrangement and recombination of genes
genotype, whereas the outcome of the inheritance, which is and thus helps in the production of variations.
visible externally or morphologically, is called phenotype. ² Synapsis: During prophase I, the maternal and paternal
² Homozygous Condition: When (in genotype of a diploid chromosomes come close to each other and together form pairs.
cell), both alleles of a character are exactly similar, then such a A pair contains two chromosomes (one maternal and one
condition is called homozygous condition. paternal) and this pair is called homologous pair. This pairing of
² Heterozygous Condition: When two alleles of a character two homologous chromosomes is called synapsis.
are not similar (and represent different allelomorphic ² Mutation: Any sudden heritable change in the genetic makeup
character) then such a condition is called heterozygous (genotype) of the organisms, (other than, which is caused by
condition. simple recombination of genes), is called mutation.

Multiple Choice Questions 1 Mark

Q. 1. Term gene was proposed by : (c) 44A + XXX (d) 44A + OO

(a) W. Bateson (b) W. Johannsen Q. 4. Chromosomal theory of inheritance was suggested by:
(c) G.J. Mendel (d) Punnett (a) Darlington (b) Belling
Q. 2. How many sons of a colour blind woman will be colour (c) Sutton and Boveri (d) T.H. Morgan
blind, if her husband is normal ? Q.5. The work of Mendel was rediscovered and
(a) All (b) 50% re-established by:
(c) 25% (d) None (a) de Vries (b) Correns
Q. 3. Genetic configuration of a super-female is: (c) Tschermak (d) All of these
(a) 44A + XO (b) 44A + XXY
 42

Q. 6. Down’s syndrome is caused due to: (c) Heterologous portion of X and Y-chromosomes
(a) Monosomy of sex- chromosome (d) Compound chromosomes
(b) Monosomy of 21th chromosomes Q.15. The unit of genetics is : (2020)
(c) Trisomy of sex chromosome (a) Chromosome (b) Genotype
(d) Trisomy of 21th chromosomes (c) Golgi bodies (d) Gene
Q. 7. Mendel dihybrid phenotypic ratio was: Q.16. The ratio of dihybrid test cross is : (2020)
(a) 9:3:3:1 (b) 12:3:1 (a) 3 : 1 (b) 1 : 1
(c) 9:3:4 (d) 9:7 (c) 9 : 3 : 3 : 1 (d) 1 : 1 : 1 : 1
Q. 8. When F1 individual is crossed with its either of the two Q.17. The development of male take place in honeybee from.
parents, the cross is known as: (2017) (2020)
(a) Test cross (b) Back cross (a) Fertilized egg (b) Unfertilized egg
(c) Reciprocal cross (d) Monohybrid cross (c) Both (a) and (b) (d) None of these
Q. 9. In Mendel’s monohybrid cross, which progeny is Q.18. Sickle cell anaemia is caused : (2020)
always heterozygous? (2016) (a) Due to the presence of recessive trait on
(a) F1 -progeny autosomal chromosomes.
(b) F2 -progeny (b) Due to the presence of Dominent trait on
(c) F3 -progeny autosomal chromosomes.
(d) Parent progeny/Generation (c) Due to the mutation and polyploidy.
Q.10. If a female with blood group O marries a male with (d) Due to the sex-linked uneffect.
blood group AB, blood group of their son can be : Q.19. Which of the following statement is correct for ‘‘Law
(2011, 16) of Dominance’’? (2020)
(a) Blood group ‘A’ (b) Blood group ‘B’ (a) Factors are in pairs.
(c) Blood group ‘AB’ (d) Blood group ‘A’ or ‘B’ (b) Determination of traits take place by factor
Q.11. Which of the following symbol is correct for Turner’s (cdiscrete unit).
syndrome? (2016) (c) If both individuals of factor pair are dissimilar,
(a) AAXO (b) AAXXY then one factor is dominant on other factor.
(c) AAXXY (d) AAXXX (d) All of these.
Q.12. Who is the founder of law of dominance and law of Q.20. Parthenogenesis is take place in : (2020)
segregation? (2019) (a) Rotifers (b) Honeybee
(a) Darwin (b) Lamarck (c) Turkis (d) All of these
(c) de Vries (d) Mendel Q.21. The development of males in honeybee take place
Q.13. How many genotypes are possible in human’s blood from: (2020)
groups? (2019) (a) Unfertilized egg (b) Fertilized egg
(a) 2 (b) 4 (c) Both (a) and (b) (d) None of these
(c) 6 (d) 8 Q.22. Which genetic disorder take place due to the trisomy of
Q.14. X-linked genes are found in : (2019) 21th chromosome? (2020)
(a) Heterologous portion of Y-chromosome (a) Klinefelter syndrome (b) Turner syndrome
(b) Heterologous portion of X-chromosome (c) Down syndrome (d) Thalassemia

Answers
1. (b) 2. (a) 3. (c) 4. (c) 5. (d) 6. (d) 7. (a) 8. (b) 9. (a) 10. (d)

11. (a) 12. (d) 13. (c) 14. (b) 15. (d) 16. (c) 17. (b) 18. (a) 19. ( d) 20. (b)

21. (a) 22. (c)

Very Short Answer Type Questions 1 Mark

Q.1. Define the term genetics? Q.2. Define dominant allele?
Ans. The branch of biology which deals with the study of Ans. In heterozygous condition only one of the two alleles
heredity and variations is called genetics. The term expresses it self phonotypically. This allele is called
genetics was coined by W. Bateson. dominant allele.
 43

Q.3. Who is the father of Genetics? (2018) Q.14. Distinguish between back-cross and test cross.
Ans. Gregor Johann Mendel (2014, 15, 17, 18)
Q.4. Mention the type of allele that expresses itself only in Ans. Refer Q.No. 10 (SA)
homozygous state in an organism? Q.15. Why Down’s syndrome is called Mongolism? (2018)
Ans. Recessive allele. Ans. The individual suffering from Down’s syndrome look
Q.5. Who gave chromosomal theory of inheritance? like a Mongolian person, so, it is called Mongolism.
(2018, 20) Q.16. Give the ratio of genotype and phenotype in
Ans. Sutton and Boveri in 1972 gave the theory of incomplete dominance and codominance. (2018)
chromosomal inheritance. Ans. In incomplete dominance in Genotype = 1 : 2 : 1
Q.6. A male has karyotype XXY. Which type of syndrome In incomplete dominance in Phenotype = 1 : 2 : 1
is this? (2007) In co-dominance in Genotype = 1 : 2 : 1
Ans. A male with karyotype XXY has klinefelter’s In co-dominance in Phenotype = 1 : 2 : 1
syndrome. Q.17. Why a colourblind man is not selected as a driver in
Q.7. Give any two example of autosomal trisomy? railways? (2019)
Ans. 1. Edward’s syndrome — Trisomy of 18th Ans. A colourblind man is not selected as a driver in
chromosome railways because he can not differentiate between red
2. Down’s syndrome — Trisomy of 21th and green colour.
chromosome. Q.18. Which syndrome is produced due to trisomy of
Q.8. Explain the law of dominance using a monohybrid chromosome number 21 in human beings? (2019)
cross? Ans. Down’s syndrome.
Or Explain law of dominance of Mendel. (2018) Q.19. Who discovered Down syndrome? Which pair of its
Ans. Refer Q.No. 20 (SA) somatic chromosome has one more chromosome? (2019)
Q.9. Name any four characters on which Mendel studied Ans. Down’s syndrome was discovered by John Langdon
inheritance. (2017) Down. 21th pair has one more chromosome.
Or How many characters did Mendel select for his Q.20. Draw the diagram of chromosomes of Turner’s syndrome.
experiment? Write the names of any two characters.
(2012, 15)
1 2 3 4 5
Ans. Mendel selected seven contrasting characters of Pea
plant for his experiment like :
Ans. 6 7 8 9 10 11 12
(i) Stem height (ii) Flower colour
(iii) Seed coat colour (iv) Pod shape 13 14 15 16 17 18 19 20
Q.10. Name two disorders in humans caused by sex-linked
21 22 X 23
inheritance. (2014, 17) Sex chromosomes
Ans. (i) Haemophilia (ii) Colour blindness
Q.21. What do you mean by sex linked traits? Write the name
Q.11. What is colourblindness? Give brief description of in-
of any two disorders caused by sex-linked inheritance
heritance of colourblindness in humans. (2015)
in humans. (2020)
Ans. A colourblind person is unable to distinguish red and
Ans. Inheritance of some of the traits in humans is
green colour. It is a sex-linked recessive disorder. It
sex-linked, i. e., they are regulated by sex-
mostly affect males because of presence of only one
chromosomes. Such traits are known as sex-linked
X-chromosome.
traits, e. g. colour blindness and haemophilia.
Q.12. What is crossing over? (2017)
Q.22. What is Turner’s syndrome? (2020)
Ans. It is the process of exchange of chromosome segments
Ans. It is caused by the absence of one X-chromosome in
between two homologous chromosomes. It result in the
female. The females has 45 ( 44 + X ) chromosomes.
formation of recombinant chromosome during sexual
Uterus is less developed, short height and webbed neck
reproduction.
are the symptoms.
Q.13. Down’s syndrome is caused by increment in which pair
Q.23. What is parthenogenesis? Give one example. (2020)
of autosome? (2016)
Ans. The process of development of unfertilized egg into the
Ans. Down’s syndrome is caused by the presence of an extra
embryo is called parthenogenesis, e. g., honey bee.
copy of chromosome number 21 (trisomy of 21
Q.24. What is Mongolism? Who discovered it? (2020)
chromosome). Individuals suffering from Down’s
Ans. Down’s syndrome is called Mongolism. It is caused by
syndrome have 47-chromosomes.
the presence of an extra copy of chromosome number
 44

on 21th autosome, i. e., trisomy. In 1866 British Q.25. What is the chromosomal formula of Turner
physician John Langdon Down discovered the syndrome? (2020)
Mongolism. Ans. AAXO.

Short Answer Type Questions 2 & 3 Marks

Q. 1. State the principle of independent assortment? coded by genes. These proteins are of two types. ‘A’
Or Write a short not on the principle of Independent and ‘B’ are called antigens. Two antibodies, which can
Assortment. (2020) react with these antigens, occur in the blood plasma.
Ans. See the answer of Long answer question-4. These are ‘a’ and ‘b’. Antibody ‘a’ reacts with antigen
Q. 2. What is co-dominance? State one example in human? ‘A’ and renders it highly sticky. Similarly, the antibody
(2011, 18) ‘b’ reacts with antigen ‘B’ and renders it highly sticky.
Or Explain co-dominance with suitable example. Depending upon the distribution of above antigens and
(2019) antibodies, four types of ABO blood groups are found
Or What is co-dominance? Explain it with suitable in human beings—
example. (2020) Blood group Antigen Antibody
Ans. Co-dominance: Co-dominance shows deviations from 1. A ‘A’ ‘b’
Mendelism, i.e., do not follow Mendelian inheritance, 2. B ‘B’ ‘a’
“The type of inheritance where the two alleles of a
3. AB A and B None
character are equally dominant and exist
4. O None a&b
simultaneously is called co-dominance.”
e. g., A and B blood group genes in human beings are Q. 5. Discuss the Inheritance of ABO blood grouping?
co-dominant. When present separately these form (2009, 15)
blood group A and blood group B. But when present in Ans. Bernstein discovered that the ABO blood grouping is
heterozygous condition, they result in the formation of an inherited characteristic which involves three allelic
blood group AB. genes, I A , I B and I O . Genes I A and I B are both
genes for genes for
antigen ‘A’ antigen ‘B’ dominant on I O and codominant for each other. Genes
IAIA IBIB I A codes for synthesis of antigen A and gene I B codes
for antigen B. Gene I O being recessive, codes for no
IA IB .... gametes antigen.
A person can naturally inherit any two of the three
IA IB allelic genes. Thus six kinds of genotypic combination
and four types of phenotypes are possible.
Blood group AB
(heterozygous) IAIA, IAIO ¾¾® Blood group A
B B B O
Q. 3. What is multiple allelism? I I ,I I ¾¾® Blood group B
A B
Ans. Mostly the inheritance of character is depend only on I I ¾¾® Blood group AB
two allelomorphic forms. But there are certain cases, O O
I I ¾¾® Blood group O
where a character has more sharp allelomorphic forms Q.6. What is incomplete dominance? Give an example.
instead of two. Such alleles are called multiple alleles. (2017)
The inheritance of these alleles is called multiple Or What is incomplete dominance? Explain with
allelism. example. (2016, 18, 19)
e. g., Inheritance of ABO blood groups in Man. Ans. Such inheritance in which the effect of dominant allele
Inheritance of ABO blood groups in man is governed is diluted or modified so that the phenotypic expression
by 3 multiple genes or alleles. These are present on the of the concerned trait in a hybrid is distinguishable
long arm of chromosome 9. These are I A , I B and I O . from both parental types is called incomplete
Q. 4. Write short note on ABO blood group? (2015) dominance.
Ans. ABO blood groups: Karl Landsteiner discovered that e. g., In Mirabilis jalapa (4’O clock Plant) or in
ABO blood group are based upon the presence of Antirrhinum majus (Snapdragon), when a cross made
certain proteins in the plasma lamina of RBC and
 45

between pure white and red flowered plants all F1 Acquired characters: These characters which acquired
individuals have pink flower. by the individual during his life time are called
On selfing, these pink flowered F1 individuals acquired characters. e. g., muscles of wrestlers, dancer
produced red, pink and white flowered plants in 1:2:1 and driver, etc.
phenotypic ratio. Q.9. Mention the difference in homozygous and
Red White heterozygous? (2015)
RR rr Parental
plant Or What is meaning of homozygous and
heterozygous? (2010, 11, 15)
R R r r gametes Ans. Homozygous: When both genes of a single trait are
same or identical, the condition is called homozygous.
Plants with this traits are also called genetically pure.
e. g., Tall ® TT,
Rr Rr Rr Rr F1 generation
(Pink) (Pink) (Pink) (Pink) Red ® RR.
Pink Pink Heterozygous: When both genes of a single trait are
Rr Rr P1 plant different or non-identical the condition is called
heterozygous or genetically hybrid individual.
R r R r e. g., Hybrid tall ® Tt
gametes
Hybrid red ® Rr
Q.10. Explain the back cross and test cross? (2014, 17)
Or Differenfiate between test cross and back cross with
RR Rr Rr rr F2 generation the help of checker board. (2020)
(Pink) (Pink) (Pink) (White)
Ans. Back cross: To confirm the purity of unit factors, when
Red Pink White F1 hybrids crossed with either one of the parental types
Phenotypic ratio : ® 1 : 2 : 1 of plants. Such a cross is called a back cross.
Genotypic ratio : ® 1 : 2 : 1 e. g . , 1:
F1 Hybrid Dominant P
Q.7. Explain the chromosomal theory of inheritance?
Dd DD
Ans. This theory was proposed by Walter Sutton and
Theodor Boveri in 1902. According to this Mendelian
D d D D
factors are located on the chromosomes which show
segregation and independent assortment at the time of
D D
transmission from one generation to the next.
This theory states that : D DD DD
1. The gametes are the bridges between one d Dd Dd
generation to next generation.
2. The two type of gametes constitute equally in the e. g . , 2:
F1 Hybrid Recessive P
heredity of the offsprings.
Dd dd
3. Nucleus contains chromosomes that carry
hereditary information.
4. There are two chromosomes of each type in an D d d d
individual as Mendelian factors.
5. Both chromosomes as well as genes occur in pairs d d
in the somatic or diploid cells. D Dd Dd
6. The paired condition of both chromosomes as
d dd dd
well as Mendelian factors is restored during
fertilization. Test cross: An individual showing the dominant
Q.8. Describe in short heredity and acquired characters? expression of a trait may be genotypically homozygous
(2017) (DD) or heterozygous (Dd) for this trait to determine its
Ans. Hereditary characters: These are the characters genotype back crossed with the recessive parental
transmitted from one generation to another e.g., hair genotype. This is called a test cross.
colour, skin colour, blood group, etc.
 46

e. g . , 1: Q. 13. Comment on sex influenced and sex limited traits.

Unknown genotype Recessive P (2018)
DD dd Ans. Sex influenced trait: Genes of these traits are located
on normal somatic chromosomes but these characters
D D d d Gamets are expressed separately in males and females because
their inheritance is dependent in sex of the individual.
D D e. g., Baldness in human.
Sex limited trait: Genes of these traits are located on
d Dd Dd All hybrid tall. autosomes but these are developed only in members of
d Dd Dd one sex.
e. g., Milk production always occur in female and beard
e. g . , 2:
grows only in men, never in women.
Unknown genotype Recessive P
Dd dd
Q. 14. A man with blood group ‘O’ marries a woman with
blood group ‘AB’. What would be the blood group of
their children? (2017)
D d d d
Ans. Phenotype Blood group ‘O’ Blood group ‘AB’
Genotype ii × IAIB
D d
Gametes i
d Dd dd 50% hybrid tall. IA IB
A B
50% homozygous I I
d Dd dd dwarf. F1-generation
i IAi IBi
Q.11. Comment on genotype and phenotype. (2010, 11, 18) (A) (B)
Ans. Genotype: The genetic configuration of an organism
Hence, offsprings will have either ‘A’ or ‘B’ blood
(in relation to the inheritance of characters) is called
group.
genotype.
e. g., DD, Dd and dd. Q. 15. A female with blood group O marries a man with blood
group ‘AB’. What can be the blood group types of
Phenotype: The outcome of the inheritance, which is
visible externally or morphologically, is called offsprings produced? Explain by sketch. (2010)
phenotype. Ans. Offspring of parent with blood group ‘O’ and ‘AB’ can
e. g., Tallness, dwarfness of plants. have blood group type A and B.
Female Male
Q.12. Why Mendel choose Pea plant as an experimental
IO IO IAIB
material?
Or Give the reasons for Mendel's success?
Ans. Mendel selected garden pea (Pisum sativum) for his
experiments because of following reasons :
1. Pea plant is a annual herb. IAIO IBIO IAIO IBIO
2. It is life span is completed in about 2-3 months. Inheritance of blood group ‘O’ and ‘AB’
3. It have more number of contrasting character.
Q. 16. Describe erythroblastosis foetalis. (2015)
4. Its gardening is easy to handle. - +
5. Pea plants are monoecious with bisexual flowers. Ans. Offsprings of RH female and RH male are RH
6. Flower structure is such that normally only self positive. Antibodies are formed against RH - antigen
pollination can occur. in female and because of its effect foetus dies either at
Reasons for Mendel’s success: the time of pregnancy or at the time of birth because
Rh-antibody causes agglutination of RBCs of foetus.
1. He performed all experiments with abrust care.
This symptom is called erythroblastosis foetalis. First
2. He continued his experiment up to several
child of such parent remains alive because antibodies
generations.
are present in less concentration. However, the second
3. He started his experiments with plants, having pregnancy is unable to proceed because foetal cells are
pure-line characters. not able to remain alive.
4. He carefully noted the results and analyzed them Q.17. Mention TH Morgan’s contribution in heredity in
statistically. brief. (2013)
5. He also used bagging methods to prevent Ans. TH Morgan did various experiments on Drosophila
self-pollination and other contaminations. melanogaster and proposed chromosomal theory of
inheritance.
 47

Morgan performed many dihybrid crosses to study sex- Ans. Variations : Offspring are not the carbon copies of
linked gene in Drosophila melanogaster, e.g., The their parents. In fact no two organisms are exactly
hybridised yellow-bodied and white-eyed females with similar. They have certain remarkable differences.
brown-bodied and red-eyed males. Dihybrid crosses These differences are known as variations. Variations
carried out in Drosophila did not resulted in 9 : 3 : 3 :1 include all changes in morphological, physiological
ratio in F2 -generation, which Mendel observed in his and behavioural characteristics (shape, size, colour,
experiments on pea. So, Morgan classified that, few relative position of body organs and habits etc).
genes present on a single chromosome inherit together, Variations are the most important basis of organic
these are called linked genes and the phenomenon is evolution because without change there can be no
called linkage. possibility of evolution.
Q. 18. A haemophilic male marries with a normal female. Kinds of variations: Broadly variations are of two
Explain transmission of this disease in their offsprings types :
by sketch. (2015, 16) 1. Somatic or Somatogenic variations
Ans. Inheritance of haemophilia in a haemophilic male and (i) These variations are caused by the effects of
normal female: Marriage of a haemophilic male to a environmental factors on the body of the
normal female, will result in all normal sons but organism.
females will be carrier of this disease. (ii) These are confined only up to a particular
Normal Haemophilic organism and lost with the death of the organism.
XX XhY
(iii) These variations do not play any significant role
from genetical and evolutionary points of view.
2. Germinal or Blastogenic or Genetical variations
(i) Germinal variations are produced due to the
XhX XY X hX XY changes in the germplasm of the organisms.
Carrier Normal Carrier Normal (ii) Since germ cells participate in gamete production
daughter son daughter son and their fusion (i.e., sexual reproduction), these
All daughters — Carriers variations are also called genetical variations
All sons — Normal because these are inheritable.
Q. 19. What are sex chromosomes? Explain their role in sex- Q.22. Explain law of dominance and law of segregation using
determination of human beings. (2018) a monohybrid cross. (2019)
Ans. Sex chromosomes are those chromosomes which Or Explain the Mendel’s law of dominance with the
determine whether the individual is male or female. help of line expression. (2020)
They are named as XY (in males) and XX (in females) Or Explain the Mendel’s law of segregation giving
chromosomes or allosome. The human males have two suitable example. (2020)
types of gametes, i. e., X and Y, while females have Ans. Law of dominance : This law states that when a cross
only one pair of gametes, i. e., XX. If an ovum gets is made between homozygous (pureline) individuals
fertilised with a sperm carrying X-chromosome, the with contrasting traits of a character then the trait that
zygote develops into female (XX) and if an ovum appears in F1 is dominant while other one is recessive.
fertilises with sperm carrying Y- chromosome, then This law explains the expression of one of the parental
zygote develops into male (XY). characters in the monohybrid cross in F1 -generation
Thus, in this way sex chromosomes play a significant and expression of both characters in F2 -generation.
role in determining sex in humans. Therefore, the phenotypic ratio in F2 -generation is 3:1.
Q. 20. Explain law of dominance of Mendel. (2018) TT tt
Ans. The law of dominance states that when a cross is made Parents (Tall) (Dwarf)
between homozygous (pureline) individuals
considering contrasting traits of a simple character then Gametes T t
the trait that appears in F1 is dominant while other one F1 Tt Selfing
which hides is recessive. This law explains the Tt × Tt
expression of one of the parental characters in the TT Tt Tt tt Phenotypic ratio : 3:1
monohybrid cross in F1 -generation and expression of (Tall) (Tall) (Tall) (Dwarf) Genotypic ratio : 1:2:1
both characters in F2 -generation. Therefore, the Law of Segregation : Due to differentiation or
phenotypic ratio in F2 -generation is 3 :1. comparative forms of a genetic trait, they remain pure
Q.21. Write a short note on variation. (2018) even when they are together. Due to which factors in
 48

the gametes are all pure. So, this is called law of purity Q.26. How is sex determined in human being? In society only
of gametes. ladies are held responsible for giving birth to female
For example, when F1 -hybrids are allowed to self- child. Why is this statement not correct? Explain it.
pollinate, then parental traits segregate in 3:1 ratio in (2019)
F2 -generation. So, contrasting traits of each allele, Or How is sex determined in human being? (2020)
transmit into different gametes by segregating from Ans. Sex determined in human being : Please see answer
each other during gamete formation. of L.A. question-5.
(Tall plant) × (Dwarf plant) Parents Women are not responsible for determination of the
TT tt
sex of a child. It is not appropriate to ill-treat a woman
Tt for giving birth to a girl child, as both males and
(Hybrid Tall) F1-generation
females are equally important for the balance of nature
Tt × Tt
and continuity of our species.
T t T t Gametes All human-beings have 23 pairs of chromosomes. A
human sperm (haploid) has 22 autosomes and one of
two types of sex chromosomes, i. e., either X or Y. On
TT Tt Tt tt F2-generation the contrary, human females have 22 autosomes that
ìï
ï
í
ïï
î

Pure Tall
(Hybrid Tall)
Pure Dwarf are exactly same as males and contain two X
Phenotypic ratio = 3:1 chromosomes. The sex of an individual is determined
Genotypic ratio = 1:2:1 by the type of sex chromosome (X or Y) contained by
The result clarifies that dwarf character which did not the sperm that fuses with the ovum.
express in F1 did not blend with tall character, but was If the fertilising sperm has an X chromosome, then the
hidden in F1 because of its recessiveness. Because of baby would be a female and if a sperm with Y
random fusion of factors at the time of gamete chromosome fuses with the ovum, it will develop into a
formation, some plants of F2 express dwarf character male child. Thus, males are responsible for
because of its pure form. determination of the sex of a child.
Q.23. Explain the following with examples : (2019) Q.27. What are genetic disorders? Describe the colour
(i) Co-dominance (ii) Incomplete dominance blindness. (2019)
Ans. (i) Co-dominance : Please see ans of Short answer Ans. Genetic disorders are inherited medical abnormalities
type question-2. caused by alteration in DNA chromosome.
(ii) Incomplete dominance : Please see ans of Short Colour blindness : Please see Long answer type
answer type question-6. question-3.
Q.24. First filial generation and second filial generation. Q.28. Explain pleiotropy and multiple inheritance. (2019)
(2019) Ans. Pleiotropy : It is the phenomenon in which a single
Ans. First filial generation or F1 is the generation of hybrids, gene product may produce multiple or more than one
phenotypic effect.
which are obtained from a cross between two
A pleiotropic gene often has a more evident effect on
genetically different parents.
one trait called the major effect and less evident effects
Second filial generation or F2 are the individuals
on other traits called secondary effects.
normally obtained after self-crossing the progeny
When a number of related changes are caused by a
obtained in F1 -generation.
pleiotropic gene, they are called syndrome.
RR rr
Parents For example : Phenylketonuria (PKU) is a defect in
(Red) (White)
which an individual lacks enzyme needed to change
Gametes R r phenylalanine to tyrosine in liver. This results in
multiple phenotypes including mental retardation,
F1 Rr × Rr eczema and pigment defects.
(Pink) Multiple or Polygenic Inheritance : The condition
Selfing where traits are controlled by three or more genes and
F2 Rr rr RR Rr the graded phenotypes are due to the additive or
(Pink) (White) (Red) (Pink) cumulative effect of all the different genes of the trait
Q.25. Explain sex determination in honeybees. (2019) e. g. human skin colour, height and intelligence.
Ans. Please see Long answer type question-2. Q.29. Differentiate between phenotype and genotype.
(2019)
 49

Ans. Difference between phenotype and genotype are given affected foetuses are themselves at risk for serious
in below table : pregnancy and delivery complications. Another
S.N Phenotype Genotype type of Alpha Thalassemia is Haemoglobin H
o. disease. There are varying degrees of
1. Phenotype is the Genotype is the Haemoglobin H disease.
morphological properties genetic makeup of an Q.32. Explain the following words with suitable examples.
and behaviour of an organism. (2020)
organism.
(i) Hybrid Vigour (ii) Incomplete dominance
2. It is not inherited by the It inherited by the Ans. (i) Hybrid vigour : Hybrid vigour is the increase in
offspring. offspring.
certain characteristics like growth rate, size,
3. It can be determined by It can be determined
observing outward by observing DNA by fertility, yield etc. of a particular hybrid organism
characters. genotyping methods. over its parents. Hybrid vigour is also known by
4. It depends on the It completely depends some other names, including heterosis and
genotype and on the gene sequences. inbreeding enhancement. Hybrid vigour occurs
environmental factors. because the hybrid offspring’s traits are enhanced
Q.30. Describe bee linkage and gene exchange. (2019) due to the mixing of genetic contributions of its
Ans. Bee Linkage and Gene exchange : In bee linkage parents.
(Drosophila), the linkage of genes on a chromosome is Hybrid vigour was first examined in a systematic
not altered and is inherited as such from generation to manner by legendary biologist and geologist
generation without any cross overs. This type of Charles Darwin. For example, when a male lion
linkage is called complete. Here the genes are closely mates with a female tiger, the resulting offspring
associated and tend to remain together. is a hybrid – a liger.
Gene exchange or Crossing over is the process that All in all, hybrid vigour can play a crucial role in
produces new combination of genes by interchanging agricultural practices. Many crops are planted to
the segments between non-sister chromatids of enhance the produce over open-pollinated
homologous chromosomes. varieties. In addition to that, hybrid vigour plays a
Q.31. Write a short note on : (2020) crucial role in evolution as well.
(i) Sickle cell anaemia (ii) Thalassemia (ii) Incomplete dominance : Please see the answer of
Ans. (i) Sickle cell anaemia : See the answer of Long Short answer type question-6.
answer question-1. Q.33. What is polygenic Inheritance? Explain it with suitable
(ii) Thalassemia : Thalassemia is a genetic blood examples. (2020)
disorder. People with Thalassemia disease are not Ans. Polygenic Inheritance : Polygenic inheritance, also
able to make enough haemoglobin, which causes known as quantitative inheritance, refers to a single
severe anemia. Haemoglobin is found in red blood inherited phenotypic trait that is controlled by two or
cells and carries oxygen to all parts of the body. more different genes.
When there is not enough haemoglobin in the red The traits that are determined by polygenic inheritance
blood cells, oxygen cannot get to all parts of the are not simply an effect of dominance and recessivity,
body. Organs then become starved for oxygen and and do not exhibit complete dominance as in
are unable to function properly. Mendelian Genetics, where one allele dominates or
There are two primary types of Thalassemia masks another. Instead, polygenic traits exhibit
disease: Alpha Thalassemia disease and Beta incomplete dominance so the phenotype displayed in
Thalassemia disease. Beta Thalassemia Major offspring is a mixture of the phenotypes displayed in
(also called Cooley's Anemia) is a serious illness. the parents. Each of the genes that contributes to a
Symptoms appear in the first two years of life and polygenic trait, has an equal influence and each of the
include paleness of the skin, poor appetite, alleles has an additive effect on the phenotype
irritability, and failure to grow. Proper treatment outcome.
includes routine blood transfusions and other Because of the inheritance mode patterns, the physical
therapies. traits that are controlled by polygenic inheritance, such
There are two main types of Alpha Thalassemia as hair colour, height and skin colour, as well as the
disease. Alpha Thalassemia Major is a very non-visible traits such as blood pressure, intelligence,
serious disease in which severe anemia begins autism and longevity, occur on a continuous gradient,
even before birth. Pregnant women carrying with many variations of quantifiable increments.
 50

Examples of Polygenic Inheritance multiple genes as well as being affected by the

(i) Skin colour : The pigment melanin is responsible environment. For example factors relating to
for dark colouration in the skin and there are at general health of a growing child such as access to
least three genes, which control for human skin food and exposure to disease, could significantly
colour. Using a hypothetical example where the affect the final height of a person. A large majority
production of melanin is controlled by of our traits are multifactorial so it is often
contributing alleles (denoted here as A, B and C), difficult to assess the effect that single genes have
resulting in dark skin colour, and therefore light on a resulting phenotype.
skin colour is produced by non contributing Q.34. What is colour blindness? If a colourblind man marrie
alleles (denoted here as a, b and c), it is possible to with a normal woman, what proportion of the sons of
see how the spectrum of different skin colors can this couple will have normal vision? (2020)
result in the offspring. Ans. Please see the answer of L.A. question-3.
It is important to remember here that in polygenic Q.35. What is sex-linked inheritance? (2020)
inheritance, alleles do not display dominance over Ans. Inheritance of some genetic characters is linked with
others, rather, each contributing allele gives an their sexes means genes controlling that specific traits
additive effect rather than a masking effect, and so are located on sex-chromosomes, these types of
the way that the alleles interact is different to characters are called sex-linked characters and their
those in Mendelian genetics. The additive effect inheritance is called sex-linked inheritance. Humans
means that each contributing allele produces one also have such characters whose genes are transferred
unit of colour. from generation to generation through linking with
(ii) Human height :Human height is an extremely sex-chromosomes.
complex inheritance pattern as there are over 400 Colour blindness and haemophilia are examples of
genes controlling for it, it is therefore extremely sex-linked inheritance in humans.
difficult to predict the height that an offspring will (i) Colour blindness : Please see the answer of L.A.
be; two short parents may produce a tall child, question-5.
whereas two tall parents can produce a short child (ii) Haemophilia : Please see the answer of L.A.
and parents with completely different heights may question-5.
produce a tall, short or intermediary child.
In addition, height is known as a multifactorial
trait, which means that the trait is influenced by

Long Answer Type Questions 5 Marks

Q.1. Write short notes on the following. chromosomes, i.e., these are monosomic for
(i) Down's Syndrome (2011, 15, 18) sex-chromosomes (2X–1 or 2A+XO).
(ii) Turner's syndrome (2011) Its body is short-statured, chest is flat and broad,
(iii) Klinefelter's syndrome (2007) neck is short and webbed, gonads absent and
accessory genital organs and external genitalia are
(iv) Phanylketonuria (v) Sickle cell anaemia.
also poorly developed. Hence these syndromes
Ans. (i) Down's Syndrome: 21st pair of autosomes in
are sterile females.
this syndrome has an additional chromosomes.
(iii) Klinefelter’s Syndrome: These syndromes are
i.e., there are three homologous chromosomes
trisomics for sex chromosomes (2X+1) = 47.
instead of two at this number, and the karyotype is
Commonly, they inherit 2A + XXY
indicated by 2x+1(21)+47.
chromosomes. Their bodies are quite like normal
The phenotype of this syndrome is a
males but due to an extra dose of X-chromosomes
short-statured and feeble minded. Its head is small
these syndromes are also remain sterile. Often
and spherical, skin warty, tongue massive, digits
breast develop (gynaecomastio).
stubby, mouth always opened and eyelids folded
Persons inheriting XYY sex chromosomes
as in the Mongols. This syndrome is therefore,
(supermales) are also known. These are fall, less
also called Mangoloid Idiocy.
intelligent, very aggressive. Superfemales with
(ii) Turner's Syndrome: These syndromes inherit a
three, four or five X-chromosomes are also
single X-chromosomes instead of two sex
known.
 51

(iv) Phenylketonuria (PKU): It is a diseased of zygote completely separate from each

condition caused by a metabolic disorder other and develop into independent embryos.
inherited as a recessive trait. The dominant gene The twins, thus formed, are obviously similar
'P' in this case codes for the enzyme, in genotype and sex, and hence called
phenylalanine hydroxilase, formed in the liver identical or monozygotic.
cells. This enzyme catalyses conversion of 3. Siamese twins: These are identical twins
phenylalanine to tyrosine. which have failed to separate completely
In homozygous recessive genotypes, absence of from each other.
this enzyme causes a high level of phenylalanine Sperm

in blood and tissue fluid. The phenotypic Ova

expresion is deterioration of CNS, possibility of
skin eczema and anomilies of teeth enamal and Zygote
bones.
(v) Sickle cell anaemia: It is a genetic disorder. In Embryonic
developement
sickle cell anaemia a change in shape of red blood
cells occurs in the venous blood. The oxygen
attaining property of these sickle shaped RBCs is
lower than normal RBCs so as a result the cell
may rupture and chronic haemolytic anaemia is
Fraternal Identical Siamese
caused. (Dizygotic) twins (Monozygotic) twins (Monozygotic) twins
The gene for sickle cell erythrocytes is Both boys or girls or one boy Both boys or girls Boys or girls
and one girl
represented by Hb S while that of normal
erythrocytes is written as Hb A . When two sickle (ii) Sex determination in honey bees: The
cell carriers, marry, they produce three types of determination of sex in honey bee is different
children- homozygous normal, heterozygous from other animals. In this case the sex is
carrier and homozygous sickle celled in the ratio determined by the number of genomes. The
of 1:2:1. genome in honey bee contains 16 chromosomes.
Carrier woman Carrier man This type of sex determination is also found in
HbA HbS HbA HbS
wasp, ants and termites. Here, the female is
diploid while male is produced without
HbA HbS HbA HbS fertilization. i.e., direct from egg so they are
haploid.
HbA HbS This phenomenon of development of male
offspring directly from the egg is called as
HbA HbAHbA HbA HbS
arrhenotoky or haploid parthenogenesis. Most of
HbS HbAHbS HbS HbS the females remain infertile and functioned as
1 Normal : 2 Carrier : 1 sickle celled workers, while only few females reproduce and
Q.2. Write short note on the following : termed as queen. They get developed due to
(i) Twins feeding on royal jelly.
(ii) Sex determination in Honey bees. (2018) Q. 3. What do you mean by sex-linked characters? Discuss
Ans. (i) Twins: When two or more offspring are produced its types and explain the inheritance of colour
from a same mother at a same time are called blindness with example. (2016, 18)
twins. Twins are of following three types. Or What is inheritance of sex linked traits? Explain any
1. Fraternal twins: Such twins are formed by one type of sex-linked inheritance in humans by
simultaneous fertilization of different ova by sketch. (2011, 13, 14)
sperms. Hence, these are like normal Ans. Sex Linked Characters: The genes of some non-sex
brothers and sisters and called dizygotic, characteristics are located on sex chromosomes. These
fraternal or non-identical twins. These vary genes are called sex-linked genes and characteristics
genetically and may be same or different that carried by such genes are called sex-linked traits or
sexes. characters.
2. Identical Twins: Sometimes, the two The inheritance of these character is called sex-linked
blastomeres resulting from the first cleavage inheritance.
52

Types of sex-linked characters: The non-sex, (ii) A cross between carrier mother and normal father:
sex-linked characteristics are divisible into three About 50% sons will colourblind and 50% will
categories. normal. 50% daughters will be carrier of such
(i) X-Linked: Those whose genes are located in the genes and 50% will be normal.
differential segments of X-chromosomes are
known as X-linked characters. Alleles of these Carrier woman
Normal man
genes never occur in Y-chromosomes. Sons can XY XCX
receive these genes only from mothers, whereas
daughter can receive these both from parents.
e. g., Colourblindness and Haemophilia. X Y XC X
(ii) Y-Linked: Those whose genes are located on the
differential segments of Y chromosomes, are
called Y linked characters. These genes are
transmitted only by father to their sons.
XCX XX XCY XY
e. g., Hypertrichosis (Presence of long and thick
hairs on ear pinnae). X CX — Carrier daughter (25%)
(iii) XY- Linked: Those whose genes are located as XX — Normal daughter (25%)
alleles in pairing segments of X and Y X CY — Colourblind son (25%)
chromosomes are called Y-linked characters. XY — Normal son (25%)
e. g., Total colourblindness and Nephritis.
Colourblindness: Colourblind phenotypes fails to
Q. 4. Describe Mendel’s principle of inheritance based on
distinguish red and green colours. Hence this effect is
dihybrid cross. (2013)
also called red-green defect or proton defect. A colour
blind person cannot become a driver, decorator, painter Or What is genetics? Explain Mendel’s law of segreg-
designer, etc. ation and law of independent assortment. (2017)
Inheritance of colourblindness: The genes of Or Describe Mendel’s law of independent assortment.
colourblindness are located only on X-sex Give its confirmation by making sketch. (2011, 13)
chromosomes. It never found on Y-chromosomes. The Ans. Genetics is the study of hereditary traits in different
genotype of female is XX, while males have XY. Its organisms.
inheritance takes place by a recessive genes ( X C ). The When a cross is done between two pairs of characters it
normal X-chromosome acts as a dominant gene. So it is is called a dihybrid cross. Mendel crossed round-
clear that a female will be colourblind only when its yellow seed variety of plants to wrinkled-green seed of
both genes are recessive, otherwise it acts as a carrier. variety plants then all plants in F1 were of round and
But males get colourblind only by one recessive ( X C ) yellow seed variety.
gene. F1 plants resulted in round-yellow, round-green
e. g., (i) A cross between a colourblind man and wrinkled-yellow and wrinkled-green seeds in the
homozygous normal woman produces normal sons and 9 : 3 : 3 :1. In this way independent expression of traits
heterozygous ( carrier) normal daughters. was described by Mendel’s law of independent
Colourblind man Homozygous assortment.
(normal) woman
X CY Law of Independent assortment : According to this
XX
law when a cross is made between two pairs of
XC Y contrasting characters, the separation of one pair of
X X
charactes is independent of separation of other
contrasting pairs of characters.
The law of independent assortment is studied on the
basis of two gene inheritance, i. e., crossing pea plants
X CX XCX XY XY with two different factors.
Normal
sons
(50%)
 53

RRYY X rryy Parental generation Female Male

(Round yellow (Wrinkled green
XX XY
seeds) seeds)

RrYy
(Round yellow seeds)
F1-generation X egg X X sperm Y
Gamete

Self-pollination
Gamete XX XY XX XY
RY Ry rY ry
Daughter Son Daughter Son
RRYY RRYy RrYY RrYy
RY (Round yellow) (Round yellow) (Round yellow) (Round yellow) Or
RRYy RRyy RrYy Rryy Criss-Cross Inheritance: The type of inheritance of
Ry (Round yellow) (Round green) (Round yellow) (Round green)
recessive sex linked character from father to daughter
RrYY RrYy rrYY rrYy
rY (Round yellow) (Round yellow) (Wrinkled yellow) (Wrinkled yellow) and then to her sons is called criss-cross inheritance.
RrYy Rryy rrYy rryy Inheritance of some genetic characters is linked with
ry
(Round yellow) (Round green) (Wrinkled yellow) (Wrinkled green) their sexes means genes controlling that specific traits
are located on sex-chromosomes, these types of
Phenotypic ratio: Round : Round : Wrinkled : Wrinkled characters are called sex-linked characters and their
Yellow Green Yellow Green inheritance is called sex-linked inheritance.
9 : 3 : 3 : 1 Humans also have such characters whose genes are
Genotypic ratio: 1 : 2 : 2 : 4 : 1 : 2 : 1 : 2 : 1 transferred from generation to generation through
Q. 5. What do you understand by sex determination? Explain linking with sex-chromosomes.
it with the help of diagram in man. (2019) Haemophilia and colourblindness are two examples of
Or What do you understand by criss-cross inheritance? sex-linked inheritance in humans.
Write two examples of recessive X-linked characters 1. Haemophilia : It is also known as bleeder’s
and explain inheritance of any one with the help of disease. Person suffering from this disorder is not
diagram. able to form clot when gets wounded. So,
Ans. Sex determination : Sex determination is a process of continuous bleeding causes death of the person.
development by which the sex of an individual is This disorder is because of X-linked recessive
settled. Sex is a method of reproduction which is gene. If a haemophilic male marries a normal
widespread among living things. It requires two female, all of the daughters in the progeny will be
individuals of the same species. carrier and all sons will be normal.
Method of sex determination in Human : Human (Haemophilic male) (Normal female)
females have two X-chromosomes and males have one XhY × XX
X-chromosome and one Y-chromosome.
All the eggs formed in females after oogenesis have Xh Y X X
one haploid set of autosomes and one set of
X-chromosomes (A+X). So, all the eggs are similar.
That is why females are called homogametic sex. XhX XhX XY XY
ì
ï
ï
í
ï
ï
î

ì
ï
ï
í
ï
ï
î

(Carrier daughters)
The sperm formed in males after spermatogenesis have (Normal sons)
one haploid set of autosomes and one set of 2. Colourblindness : Person suffering from this
X-chromosomes, while some other sperms have one disorder is not able to distinguish red and green
set of autosomes and other of Y-chromosomes (A+X or colours. Gene controlling colourblindness is
A+Y). So, two types of sperms are formed. located on X-chromosome and is recessive.
50% sperms are (A+X) and remaining 50% sperms are For example, when a colourblind female marries a
(A+Y) that is why males are called heterogametic sex. normal male then progeny will have a colourblind
At the time of fertilisation, if (A+Y) sperm males and females will be carrier of disorder.
consolidates with the egg, it produces a male child. If
egg consolidates with (A+X) sperm, it produces female
child.
 54

(Colourblind female) (Normal male) Ans. Inheritance : The process by which character pass
XCXC × XY from one generation to the next is called inheritance.
The study of hereditary traits in different organisms is
XC XC X Y
called genetics.
Mendel’s law of independent assortment : Please see
XCX XCX
Long answer type question-4.
XCY XCY
ì
ï
ï
í
ï
ï
î
Q. 8. What do you mean by genetical disorder? Differentiate

ì
ï
ï
í
ï
ï
î
(Carrier daughters) (Colourblind sons)
between sex limited and sex influenced genes.
Q. 6. What is sex determination? Describe the mechanism of Comment upon haemophilia. (2019)
sex determination in humans and honey bees. Ans. Genetic disorders are the abnormalities caused due to
(2019, 20) the absence or excess or abnormal arrangement of one
Ans. Sex determination and mechanism of sex or more chromosomes. These disorder are not inherited
determination in human being : See answer of Long like Mendelian traits.
answer question-5. Differentiate between sex limited and sex influenced
Sex determination in honey bees : See Answer of genes : Please see Short answer type Q. 13.
L.A. question-2. Haemophilia : Please see Long answer type
Q.7. Define inheritance. Describe Mendel’s law of question-5.
independent assortment. (2019)

NCERT Fully Solved Exercise

Q.1 Mention the advantages of selecting pea plant for (c) Monohybrid and Dihybrid : If in a cross, only
experiment by Mendel. one character is considered at a time for analysis,
Ans. Mendel selected Garden pea (Pisum sativum) for his the cross is called a monohybrid cross. On the
experiments because of following advantages : other hand if two characters are considered
— Short life span. simultaneously, the cross is called as dihybrid
— Bisexual nature of flower. cross.
— Suitable structure and shape of flower for Q.3 A diploid organism is heterozygous for 4 loci, how
cross-pollination. many types of gametes can be produced?
— More number of contrasting characters. Ans. 16 types of gametes can be produced.
— Self-fertilisation could easily be controlled. Q.4 Explain the Law of Dominance using a monohybrid
Q.2 Differentiate between the following : cross.
(a) Dominance and Recessive Ans. Please see the answer of S.A. type question-22.
(b) Homozygous and Heterozygous Q.5 Define and design a test-cross.
(c) Monohybrid and Dihybrid. Ans. A test cross is a back cross, which involves the cross
Ans. (a) Dominance and Recessive : When two factors of between F1 offspring with homozygous recessive
a pair are in heterozygous condition, then only (double recessive) parent. The test cross is used to
one factor is able to express itself, while other one determine the homozygous or heterozygous nature of
remains hidden. The factor, which is able to the F1 offspring. For figure refer Q.No. 10 (SA).
express itself, is called dominant factor while the Q.6 Using a Punnett Square, workout the distribution of
other factor is called recessive factor. phenotypic features in the first filial generation after a
(b) Homozygous and Heterozygous : When (in cross between a homozygous female and a
genotype of a diploid cell), both alleles (factors) heterozygous male for a single locus.
of a character are exactly similar, then such a Ans. In this case, the female is AA while male is Aa. A cross
condition is called homozygous condition. On the between them gives following genotypes in F1 (first
other hand, if two alleles (factors) of a character filial) generation :
are not similar (and represent different AA, Aa, AA, Aa, i.e., phenotypically all are dominant.
allelomorphic character) then such a condition is A Punnett square distribution will be :
called heterozygous condition.
 55

Q.10 How is sex determined in human beings?

Ans. Please see answer of L.A. type question-5.
Q.11 A child has blood group O. If the father has blood
group A and mother blood group B, work out the
genotypes of the parents and the possible genotypes of
the other offsprings.
Ans. For blood group O, only one genotype is possible—
Q.7 When a cross is made between tall plant with yellow
seeds (TtYy) and tall plant with green seed (Ttyy), I O I O . So, both parents must contain one I O allele. So,
what proportions of phenotype in the offspring could possible genotypes of the parents must be I O I A and I O
be expected to be : (2020) I B.
(a) tall and green Parents with such genotypes can produce offsprings
(b) dwarf and green with all types of blood groups.
Ans. Tall plant with yellow seeds (TtYy) forms following Q.12 Explain the following terms with example :
four types of gametes : (a) Co-dominance.
TY , T y , tY and ty (b) Incomplete dominance.
Tall plant with green seed (Ttyy) forms following two Ans. (a) Co-dominance : The type of inheritance where
types of gametes : the two alleles of a character are equally dominant
T y and ty and exist simultaneously is called co-dominance.
A cross between these plants gives following results : (b) Incomplete dominance : The type of inheritance
where the two alleles of a character interact in
such a way, so as to cause the blending of the
character is called incomplete dominance (or
blending inheritance).
Q.13 What is point mutation? Give one example.
Ans. Point mutations are the changes, which affect a very
specific portion of the DNA (gene) such as a
In this way out of a total of 8 plants — nucleotide. These mutations therefore directly
(a) Tall and green plants are 3, i.e., 3/8 influence the nature and functioning of the genes.
(b) Dwarf and green 1, i.e., 1/8. Since genes carry genetic information in the form of
Q.8 Two heterozygous parents are crossed. If the two loci genetic codes, any change in the nucleotide sequence
are linked, what would be the distribution of and nature can affect the expression of gene adversely.
phenotypic features in F1 generation for a dihybrid Q.14 What are mutations?
cross? Ans. These are sudden and random changes in the genetic
Ans. If the two loci are linked completely, the phenotypic material of an organism.
features in F1 generation for a dihybrid cross would be Q.15 Who had proposed the chromosomal theory of the
the same as that of parents. But if the two loci are linked inheritance? What are the important features of this
partially, the phenotypic features in F1 generation for a theory? (2020)
dihybrid cross would have parental types as well as Ans. Refer Q.No. 7 (SA).
recombinant types. The ratio between parental types Q.16 Mention any two autosomal genetic disorders with
and the recombinant types would depend upon the their symptoms.
strength of linkage, i.e., more the linkage, more would Ans. The two genetic disorders are :
be the parental types. (a) Down’s syndrome : This is due to trisomy of 21st
Q.9 Briefly mention the contribution of T.H. Morgan in pair of chromosome. The affected person has
genetics. large, round face and is mentally retarded.
Ans. T. H. Morgan was one of the supporters of Batson and (b) Sickle cell anaemia : This is due to the formation
Punnett’s concept of linkage (Coupling and repulsion). of abnormal haemoglobin. The RBCs of the
He provided experimental support to the theory of person becomes sickle shaped and have very
linkage. He especially mentioned about the sex linkage small amount of haemoglobin.
in fruit flies, Drosophila malanogaster.
ccc
 56

Chapter

6 MOLECULAR BASIS
OF INHERITANCE

² Base pairs: A set of two bonded nucleotides on opposite ² Restriction enzyme: An enzyme normally found in bacteria
strands of DNA. There are two possible base pairs: C-G and A-T. which cuts DNA at specific sites (i.e., each time a specific
² DNA polymerase: An enzyme which repairs DNA by nucleotide pattern occurs). Because a restriction enzyme always
facilitating the formation of hydrogen bond between a acts upon DNA in the same manner, a map can be made of a
nucleotide on a broken piece of DNA, such as a nicked or restriction enzymes actions on a known set of nucleotides.
single-stranded piece of DNA as created in the laboratory, and ² VNTR: The DNA of a person contains specific short sequences
the individual nucleotide it needs to form a complete and stable of nucleotides, which are repeated throughout the length of the
base pair. DNA molecule. These nucleotide repeats are called VNTRs
² Homology: The degree to which two pieces of DNA match, or (Variable Number of Tandem repeats).
complement each other (two pieces of DNA are complementary ² PCR: PCR (polymerase chain reaction) is a technique, with the
if their respective nucleotides, in their current order, match C to help of which a small amount of DNA can be amplified (i.e.,
G and A to T). If one piece of DNA is 100% complementary to multiple copies can be obtained).
another piece of DNA, they demonstrate very high homology; if ² Transcription: The process of formation of RNA from a DNA
the pieces are only able to form a handful of base pairs between piece is called transcription. This process is the first step in the
their corresponding nucleotides, they demonstrate very low synthesis of a protein.
homology. ² Translation: The process fo actual assembling of amino acids
² Hybridization reaction: A process in which a probe binds to on a ribosome, to synthesise a polypeptide chain is called
a Southern blot if the probe’s DNA sequence and the DNA on the translation.
Southern blot match. ² Bioinformatics: It is a new area of study which involves the
² Probe: A radioactive strand of DNA often used to find use of living material such as DNA and proteins, for data
particular sequences in a Southern blot. management.

Multiple Choice Questions 1 Mark

Q. 1. The DNA, which was described by Watson, Crick and (a) Meselson and Stahl
Wilkins was: (b) Hershey and Chase
(a) A-DNA (b) B-DNA (c) Griffith
(c) Z-DNA (d) C-DNA (d) Watson and Crick
Q. 2. Jumping genes are also called: Q. 5. Okazaki fragments are synthesized on :
(a) Oncogenes (b) Transpozons (a) both leading and lagging strands of DNA
(c) Pseudo genes (d) Chimera (b) leading strand of DNA only
Q. 3. Molecular scissors are: (c) lagging strand of DNA only
(a) Restriction endonuclease (d) complementary DNA
(b) Exonuclease Q. 6. Which one of the following has dual functions, it codes
(c) Lipase for methionine and also act as initiator codon?
(d) RNA polymerase (a) AUG (b) AUC
Q. 4. Transformation was discovered by : (c) ACU (d) ACA
 57

Q. 7. Messenger RNA is produced in : (2017) (c) Discovery of DNA

(a) Nucleus (d) Discovery of DNA ligase enzyme
(b) Ribosome Q. 9. Which of the following is initiating codon? (2014)
(c) Golgi body (a) AUG (b) AUU
(d) Endoplasmic reticulum (c) UAG (d) UUU
Q. 8. Har Gobind Khorana is known for : (2015, 17) Q.10. Displacement of thymine in RNA by : (2018)
(a) Protein synthesis (a) Guanine (b) Uracil
(b) Discovery of RNA (c) Cytosine (d) Adenine
Answers
1. (b) 2. (b) 3. (a) 4. (c) 5. (c) 6. (a) 7. (a) 8. (a) 9. (a) 10. (b)

Very Short Answer Type Questions 1 Mark

Q. 1. What are the Okazaki fragments? Q. 9. What is genetic code? (2016)
Or What are Okazaki fragments? Which enzyme Ans. It is the sequence of base triplet in a DNA molecule
participate in their joining? (2019) which determines a polypeptide.
Ans. In 1968 Reiji Okazaki discovered that the new DNA Q.10. Describe the difference between prokaryotic and
strand is synthesized in small separate pieces or eukaryotic DNA. (2012, 17)
fragments which are later joined with each other by Ans. Histone proteins are not associated with prokaryotic
DNA ligase enzyme. The fragments which are joined DNA, whereas histones proteins are associated with
to form it were later name Okazaki fragments. eukaryotic DNA. Prokaryotic DNA is circular in shap,
Q. 2. What are initiation codon and termination codon? whereas eukaryotic DNA is linear.
(2017) Q.11. Write the functional unit of gene. (2013)
Or Name of the initiation and termination codons in Ans. The functional unit of the gene is called cistron.
protein synthesis. (2018) Q.12. Write the definition of genome. (2017)
Ans. Initiation codon – AUG Or Define the genome. (2019)
Termination codon – UGA, UAA and UAG Ans. A haploid set of chromosome found in the organisms,
Q. 3. What are housekeeping genes? which is inherited by the gametes, is called genome.
Ans. Such genes of a gene pool which direct the synthesis of Q.13. Write difference between nucleoside and nucleotides.
proteins or RNA of similar characters in all cells of an (2010, 14)
organism according to species are called housekeeping Ans. Nucleotide is a complete unit of nucleic acid, whereas
genes. nucleoside lack a phosphate molecule. Nucleotides are
Q. 4. What is translation? acidic and nucleosides are basic.
Ans. The polymerization of amino acid to form polypeptide Q.14. Who proposed the famous double stranded helical
with the help of mRNA, ribosome, and tRNA is called structure of DNA. (2011)
translation. Ans. James Watson and Francis Crick in 1953.
Q. 5. Define an anti-codon? Q.15. Name the enzyme that Joins the fragments of DNA
Ans. The triplet base present on the tRNA which is during replication. (2018)
complementary to codon on mRNA is called Ans. Ligase
anti-codon. Q.16. How many nucleotide units in DNA? (2018)
Q. 6. What do you mean by non-sense codon? Ans. Four or Infinitine.
Ans. The codon which do not code for any amino acid and Q.17. Who identified first the DNA as an acidic substance
leads to termination of translation process is called present in nucleus ? (2019)
non-sense codon. These are UAA, UAG and UGA. Ans. Friedrich Meischer identified first that DNA is an
Q. 7. Who proposed the operon concept? acidic substance present in the nucleus.
Ans. Jacob and Monod. Q.18. Which enzyme participate in the formation of DNA
Q.8. What is monocistronic mRNA. from DNA? (2019)
Ans. mRNA that contains information for the formation of Ans. DNA polymerase enzyme.
only one polypeptide chain is called monocistronic
mRNA.
 58

NH2
Q.19. Draw diagram of any two nucleotides of DNA. (2019)
O O N
O H— N
N (ii) O—P—O
H— NH – CH2 N N
Ans. (i) O—P—O O O H
– CH2 N N NH2
O O
H H H H
H H H
OH H
OH H Q.20. Which enzyme cut to DNA at specific site? (2020)
Ans. Restriction endonuclease enzyme.
Q.21. Give two chemical difference between DNA and RNA.
(2020)
Ans. Please see the answer Short Answer Type question-8.
Q.22. Define the term promoter. (2020)
Ans. Please see the answer of Q-11 of NCERT exercise.

Short Answer Type Questions 2 & 3 Marks

Q.1. Give the applications of DNA fingerprinting? after exposer to the DNA of another genotype is called
(2016, 17) Griffith's effect or transformation.
Or DNA is a genetic material. Discuss. (2019) Biochemical explanation of Griffith's experiment was
Ans. DNA fingerprinting is being used for a wide variety of given by three scientists Oswald Avery, Colin
purposes, the most common of which are convicting MacLeod and Maclyn McCarty in 1944. They purified
criminals and freeing the innocent. It is also used to proteins, DNA and RNA from the heat killed S cells to
solve the paternity disputes. This technique is also used see which ones could transform live R cells into
for determining population and genetic diversities. It is S-cells. They discovered that DNA alone from S
used to identify the social groups origin, historical bacterium caused R bacteria to become transformed.
migrations and invasions. Injected into
Q.2. Why is DNA regarded as the genetic material explain?
(2015) Mouse dies
Ans. Initially, most biologists through that protein was the S-strain Bacterial
genetic material. Over a period of roughly 25 years culture S-strain recovered
Mouse
(1928-1952) the geneticists become convinced that
DNA was the genetic material, not protein. The most
conclusive evidences in support of DNA as the genetic Mouse survives
material comes from the following experiments. R-strain
Bacterial
Transformation experiment of Griffith: 1928, a culture Mouse S-strain not found
British medical officer named Fredrick Griffith
published an important paper on Streptococcus
pneumonia a bacterium that causes pneumonia in Heat killed Mouse survives
S
humans and other mammals. He prepared the two
S-strain
strains of these bacterium ‘S’ strain (pathogenic) ‘R’
Mouse S-strain not found
strain (non- pathogenic).
In his experiment Griffith injects these strains of mice
as follows—
R-strain
1. 'S' strain ¾® Injects into mice ¾® mice die
Mouse dies
2. 'R' strain ¾® Injects into mice ¾® mice live Heat killed
S
3. 'S' strain (heat killed) ¾® Injects into mice
¾® mice live S-strain S-strain not
Mouse recovered
4. 'S' strain (heat killed) + R strain live
Fig. Griffith’s transformation experiment
¾® Injects into mice ¾® mice die
In Griffiths fourth experiment, he showed that the Q.3. Name the different types of RNA molecules, taking
strain R bacteria had absorbed DNA from the heat part in protein synthesis? (2017, 18)
killed strain 'S' bacteria, causing the genotype of the Or How many types of RNA are found on the basis of
bacteria to change. A change in the genotype of cell function?
 59

Or Write the name of three type RNA found in cell and Ans. Chargaff proposed following conclusions after
give the function each of them. (2020) studying DNA of various organisms.
Ans. For protein synthesis there are three types of RNA (i) Amount of purine and pyrimidine bases is equal in
molecules are found in a cell. all DNAs.
1. Ribosomal RNA (r-RNA): These are structural A + G = T + C.
components of ribosomes. These constitute about (ii) Number of adenine remains equal to the number
80% of the total RNA pool of cells. Ribosomes are of thymine and cytosine remains equal to guanine.
super molecular complexes whose 65% mass A = T and C = G
consists of RNAs and 35% of proteins. (iii) Adenine + Thymine and Guanine + Cytosine ratio
Function: Ribosomal RNA (rRNA) molecules is different in different species but some in
form the core of a cell’s ribosomes (the structures common species.
in which protein synthesis take place). Q. 6. Differentiate between leading and lagging strands of
2. Messenger RNA (m-RNA) : These are the only parental DNA?
RNAs which actually translate genetic Ans.
informations into proteins. In 1961, Francis Jacob Leading strand Lagging strand
& Monod named these molecules as messenger 1. This strands lies in the This strand lies in opposite
RNA. In the cytoplasm mRNA molecules become correct direction for directions.
attached to ribosomes and serve as templates. replication.
mRNA molecules are rapidly degraded after 2. Synthesis on this strand is The synthesis on this strand
protein synthesis. And constitute about 2% of the continuous. is discontinuous.
total RNA pool of cells. 3. Synthesis on this strand A large number of primers
Function: Messenger RNA (mRNA) molecules needs a single primer. are required.
carry the coding sequence for protein synthesis 4. The direction of growth of Direction of growth of
daughter DNA is 5'–3'. daughter strand is from 3'
and are called transcripts. to 5'.
3. Transfer RNA (t-RNA): t-RNA, often called
soluble RNA (sRNA), constitute about16 to 18% It was discovered by Alac Jeffrey's et al. in 1995. Prof.
of the total RNA pool of cells. These are relatively Lalji Singh is considered as father of Indian DNA
small with 73-94 ribonucleotide residues. They fingerprinting. It is technique used for identification of
transfer the amino acids from cytosol to the individual on the basis of their DNA profile. It is
ribosomes. popularly known as DNA profiling or DNA typing.
Function: Transfer RNA (tRNA) molecules carry As we know that 99.9% of base sequence is the same.
amino acids to the ribosomes during protein Only 0.5% difference in sequence of DNA which make
synthesis. every individual unique. It is a very quick way to
Q.4. What is genetic code? Write any four characteristics of compare the DNA sequence of any two individuals.
it. (2020) This process involves identifying differences in some
Ans. Genetic code is that sequence of nitrogenous bases specific regions in DNA sequence called repetitive
present in mRNA, where information regarding protein DNA or mini-satellite or Variable Number Tandon
synthesis is stored. 1961 regarding protein synthesis is Report (VNTR). These sequence show high degree of
stored. 1961 Francis Crick and Sydney Benner polymorphism and form a basis of DNA finger
provided the proof that genetic information of each printing.
amino acid is encoded in a specific sequence of three Technique of DNA profiling
successive nucleotides, forming a triplet code, called (i) Source of DNA : WBCs, blood, saliva, semen,
“codon”. Thus a codon is the smallest unit of genetic vaginal swabs, skin cells, hair roots etc. are used
information. as source of DNA for DNA printing.
(ii) Isolation of DNA : DNA source is exposed to high
Features of Genetic codon:
speed refrigerated ultracentrifugation. It separates
1. Genetic codes are the nucleotide triplets. 2. Genetic
the nuclei and breaks the same to release DNA.
codes are universal. 3. Genetic codes are linearly
(iii) Amplification of Isolated DNA : The amount of
arranged and non-overlapping. 4. Genetic codes are
DNA is small so the extract is amplified through
unambigous. 5. Genetic codes are degenerate. 6. Genetic
polymerase chain reaction (PCR).
codes are comma-less.
(iv) Digestion of DNA By R.E.: With the help of
Q.5. Explain the chargaff's rule in brief? (2009, 12)
restriction endonuclease enzyme DNA is cut to
separate VNTRs.
 60

(v) Separation of DNA Fragments by Electrophoresis : 1. It is dark in colour when It is light in colour when
The fragments DNA is exposed to electrophoresis stained with chromosomal stained with chromosomal
stains. stains. Thus, it is not
over agarose gel. It separates DNA fragments. visible under microscope.
The separated DNA segments (VNTRs) are also
2. This is condensed part of This is loose part of chro-
known as restriction fragment length chromosome which is mosome means less cond-
polymorphism (RELP). present all around nucleus. ensed in comparison to
(vi) Single stranded DNA : VNTRs are treated with chromosomes of the cell.
alkaline chemicals to split them into ss-DNA. 3. DNA replication occurs DNA replication occurs
(vii) Southern Blotting : VNTRs are now transferred to late in heterochromatin. soon. So, genes are very
So, its genes are always active.
synthetic membrane of nitrocellulose or nylon inactive.
placed over the gel.
4. This part is inactive for This part is active for
Q.7. What is deoxyribose sugar? Make molecular structure transcription. transcription.
of this sugar. (2012, 14)
Q.10. Write differences between prokaryotic DNA and
Ans. This sugar is found in DNA. It contains 5 carbons. It’s
eukaryotic DNA.
fifth carbon molecule is out of the ring. It’s first carbon
molecule is always attached with nitrogenous base by Ans. Prokaryotic DNA Eukaryotic DNA
glycosidic bond. Third and fifth carbon are attached 1. Amount of DNA is very Amount of DNA is very
with phosphate molecule. Two sugars are attached less (low C-value). high.
with each other with phosphodiester bond between 2. DNA is not present in DNA is enclosed within
third and fifth carbon with phosphate molecules. nucleus or any organelle. nucleus.
5 3. DNA lies in the DNA lies in nucleoplasm
HOCH2C O OH cytoplasm. (not in cytoplasm).
4 1 4. DNA is not associated DNA is associated firmly
HH H H with histone proteins. with histone proteins.
3 2 5. Single molecule of DNA Several molecules of
OH H is present. DNA are present.
Q.8. Write the difference between DNA and RNA. Q.11. Define following :
(2010, 11, 12, 13, 14, 17) (i) Jumping gene (2010)
Or Write any six difference between DNA and RNA. (ii) Operon (2009, 10)
(2019) (iii) Exon and intron (2009)
Ans. The differences between DNA and RNA are as follow: Ans. (i) Jumping gene : Some genes change their
DNA RNA location in the DNA of the eukaryotic cell. These
are called jumping genes. Dr. Barbara
1. It is mainly found in It is mainly found in
nucleus. cytoplasm. McClintock (1950) discovered jumping gene in
2. In this, polynucleotide It is usually linear.
maize plant.
chains are found in the (ii) Operon : A group of closely placed structural
coiling state. genes and related genes is called operon.
3. Pentose sugar is in Pentose sugar is in ribose Operon = Regulatory gene + Promoter gene
deoxyribose form. form. + Operator gene + Structural gene.
4. Thymine base is present Uracil base is present and (iii) Exon and Intron : Active regions of DNA in
and uracil is absent thymine is absent. eukaryotic cells that contain codes for protein, are
5. It is the universal genetic It is the genetic material in called exon whereas inactive regions of DNA
material. some viruses. which do not contain any codes are called introns.
6. In all organisms, DNA is In most organism, RNA is Q.12. Draw labelled diagram of a nucleosome and name the
identical and similar. found in three forms— protein associated with it. (2019)
mRNA, tRNA and rRNA. DNA H1 histone

Q.9. Differenciate between Euchromatin and

heterochromatin. (2010)
Histone octamer
Ans. Following are differences between euchromatin and Ans.
heterochromatin.
Heterochromatin Euchromatin Core of histone
molecules Nucleosome
 61

The nucleosome is made up of four types of proteins Ans. A nucleotide (DNA/RNA) is composed of a
H 2 A, H 2 B, H 3 and H 4 occurring in pairs. nitrogenous base, pentose sugar and a phosphate
Q.13. How did Hershey and Chase prove that DNA is the group.
genetic material? (2019) â There are two types of nitrogenous bases purines
Or DNA is a genetic material : Prove it with (adenine and guanine) and pyrimidines (cytosine,
experiment. (2020) uracil and thymine). Cytosine is common for both
Ans. Hershey and Chase experiment: DNA and RNA, while thymine is present in DNA
(i) They grew some bacteriophages on a medium that and uracil is present in RNA in place of thymine.
contained radioactive phosphorus and some in â Ribose sugar is present in RNA and Deoxyribose
another medium that contained radioactive sugar is present in DNA.
sulphur. â A nucleotide (deoxynucleotide) is formed,
(ii) Viruses grown in the presence of radioactive depending upon the type of sugar present when a
phosphorus contained radioactive DNA, but not phosphate is linked at 5¢OH of nucleoside through
radioactive protein as phosphorus is present only phosphodiester linkage. Nucleotides joining through
in DNA. a 3¢ - 5¢ phosphodiester linkage may join to from a
(iii) Viruses grown on radioactive sulphur contained polynucleotide chain.
radioactive protein, but not radioactive DNA â In RNA, there is an additional —OH group at 2¢
because DNA does not contain sulphur. position in the ribose of every nucleotide residue.
(iv) It was found that bacteria which were infected Q.16. On which basis an RNA is called messenger RNA or
with bacteriophages that had radioactive DNA transfer RNA? Explain. (2019)
were radioactive, indicating that DNA was the Ans. The RNA molecule is mainly of three types, i. e.,
material that passed from the virus to the bacteria. mRNA, tRNA and rRNA. Out of these, mRNA or
(v) Bacteria that were infected with viruses that had messenger RNA brings instructions from the DNA for
radioactive proteins were not radioactive. This the formation of particular type of polynucleotide.
indicated that proteins did not enter the bacteria The mRNA molecule contains cap region (controls the
from the viruses. rate of protein synthesis), non-coding region-1, coding
(vi) This was a clear cut proof that DNA is the genetic region non-coding region-2 and Poly A sequence
material that is passed from virus to bacteria. (protects the mRNA from cellular enzymes and helps
Bacteriophage in detachment from ribosome. Only 0.025% part of
Radioactive (32P)
Radioactive (35S) labelled labelled DNA
protein capsule total DNA content codes for tRNA. The tRNAs carry
amino acids for initiation codes and called transfer
RNA or adaptor RNA. The tertiary structure of tRNA
Bacteriophage
Bacteriophage
contains five arms each with 100p and a stem. These
release DNA
Infection release DNA are as follows :
AA-binding site (amino acid binding site), anticodon
Bacteriophage arm (recognition site of tRNA), TyC arm (site for
separate from Bacteriophage attaching to ribosome, D-arm (binding site for
bacteria release DNA
Blending
Bacteriophage Bacteriophage aminoacyl synthetase enzyme) and variable arm.
DNA
DNA Q.17. Describe DNA fingerprinting. (2019)
Centri- Ans. Please see NCERT que. 13.
fugation
35
No radioactive { S} 35 Q.18. Comment upon human genome project. (2019)
No radioactive { S}
detected in cells detected in cells Ans. Human genome project : Please see NCERT ques. 12.
+ +
35
No radioactive { S} 35
No radioactive { S}
Q.19. Difference between purine and pyrimidine base. (2020)
detected in supernatant detected in supernatant Ans.
Fig. The Hershey and Chase experiment
Purine base Pyrimidine base
Q.14. Draw labelled diagram of double helix DNA model 1. These have two carbon- These have one carbon-
proposed by Watson and Crick. (2019) nitrogen ring and four nitrogen ring and two
nitrogen atoms. nitrogen atoms.
Ans. Please see the ans of Long answer type question-5.
2. These have comparatively These have comparativly
Q.15. Write in short the chemical composition of high melting point and low melting point and
polynucleotide chain of DNA and RNA. (2019) boiling point. boiling point.
 62

3. These are synthesised by These are synthesised by Q.21. Difference between codon and anti-codon. (2020)
Traube purine synthesis Biginelli reaction.
method.
Ans.
Codon Anti-codon
Q.20. Difference between B-DNA and Z-DNA. (2020) 1. Codon is located on the Aniti-codon is located on
Ans. mRNA molecule. the t-RNA molecule.
B-DNA Z-DNA 2. These present on the These present on tRNA
1. These forms under normal These forms under high mRNA sequentially. individually.
physiological conditions. salt concentrations. 3. These determines the These brings the specified
position of the amino acid. amino acid by the codon.
2. These are right-handed. These are left-handed.
4. These are complementary These are complementary
3. These contain a wide and These contain a narrow to the nucleotide triplet in to the codon.
deep major groove and a and deep major groove and the DNA.
narrow and deepminor a wide and shallow minor
groove. groove. Q.22. Draw a labelled diagram of double helical model of DNA
4. The orientation of sugar The orientation of sugar
presented by Watson and Crick. (2020)
residues are altering. residues are not altering. Ans. Please see the answer of L.A. question-5.
Q.23. What do you understand by DNA fingerprinting? (2020)
5. Their repeating unit is Their prepeating unit is
Ans. Please see the answer of question-13 of NCERT
mononucleotide. dinucleotide.
exercise.
6. The angle of twist per The angle of twist per Q.24. Write a note on semi-conservation replication of DNA.
repeating unit is 36°. repeating unit is 60°.
(2020)
7. These diameter is 20Å. These diameter is 18Å. Ans. Please see the answer of L.A. question-4.

Long Answer Type Questions 5 Marks

Q. 1. What do you mean by regulation of gene expression? A. Structural genes: It actually encode the related
Describe the Operon Model in case of lactose enzymes or other proteins. These are–
metabolism in E. coli ? (i) Cistron Z – codes for b - galactosidase
Ans. Gene expression: Obviously, various types of proteins enzymes
participates in the formation of each part of a cell, and (ii) Cistron Y - codes for permease enzyme.
there is a need of functional proteins or enzymes for the (iii) Cistron A - codes for transacetylase enzyme.
stimulation and conduction of metabolic reactions of a B. Controller genes: It regulates the activity of
cell. Hence the synthesis of structural and functional structural genes by inducing or repressing
proteins in the cell under control of DNA as need is method. These are of three types.
called gene expression. (i) Regulator genes. It is called R-gene. It
Regulation of Gene expression: The induction of synthesizes a special type of enzyme which
proteins or enzymes synthesizing genes and repression acts as a repressor. It binds to operator gene
of unwanted genes is carry on in the cell. This process and loose their activity.
is called regulation of gene expression, also known as (ii) Promoter gene: It is that part of DNA where
RNA polymerase binds and initiates the
gene control of protein synthesis.
transcription of structural gene.
Lac Operon model in 1961 Jacob and Monod
(iii) Operator gene: It is that part of DNA that
discovered in E.coli that a group of three genes remain
regulates the transcription of m-RNA from
associated with three enzymes that metabolize lactose. structural genes.
The genes that code for these enzymes are transcribed Working of Lac operon :
only when the enzymes are needed. For the regulation 1. In the absence of lactose: The lactose operon is
of these genes Jacob and Monod produced on operon shut off. The regulatory gene of the lactose operon
concept and were awarded by Nobel prize 1965. directs of a protein called a repressor protein,
Structure of Operon Model: Prokaryotic gene (DNA) which binds to the operator site. RNA polymerase
is often organised in coherent packages called operons, although still able to bind to the promotor, cannot
in which the genes for related functions lie close to one get past the repressor protein to transcribe the
another. An operon consists of following parts :
 63

Operon 1. Binding of RNA polymerase: The first step of

Promoter
Promoter gene Operator RNA synthesis is binding of RNA-polymerase to
gene gene Structural genes
Regulatory gene specific DNA segment called promoter site. This
P LAC I P O LAC Z LAC Y LAC A binding is helped by certain proteins called
transcription factors.
No RNADNA E. or coli (a) The segment of 35 nucleotides which have
formation bacteria TTGACA base sequence the sigma factor of
Repressor mRNA Repressor bind with RNA polymerase enzyme joint to DNA of
operator region
this site.
(b) Pribnow box is made up of 6-10 nucleotides.
In absence of inducer
In prokaryotes the base sequence of its
Repressor
TATAAT and in eukaryotes it is TATAAAT.
Fig. Lac operon model
It is known as Hogness box or TATA box.
structural genes. Consequently the lactose 2. Initiation: In the second step the RNA polymer are
metabolizing enzymes are not synthesized. enzyme unwinds the DNA duplex and separates
2. In the presence of lactose: When lactose is present its two strands at the start point. The enzyme then
medium promoter enters into and form begins the synthesis of RNA chain at the start
repressor-inducer complex by binding repressor. point on the template strand of DNA.
Due to this complex repressor cannot bind to 3. Chain Elongation: After initiating the
operator site. Now it induces to RNA polymerase transcription the RNA polymerase enzyme moves
to bind with initiating site of promoter gene. Thus towards 5' end of the strand, catalyzing
polycistronic lac m-RNA transcribed. This polymerization of RNA by joining incoming
m-RNA encoded all the three enzymes which phosphorylated ribonucleotides one by one
essential for reduction of lactose. phosphodiester bonds.
P LAC I P O LAC Z LAC Y LAC A The elongating RNA transcript regularly keeps
DNA or E. coli
bacteria separating from template strand and certain
Transcription proteins reform DNA duplex and re-assembles
Repressor mRNA nucleosides behind the advancing RNA
Z LAC mRNA Y A
polymerase.
Translation 5¢
3¢
DNA helix
Repressor 3¢
protein b-Galactosidase Primerase Transacetylase 5¢
Promotor site Terminator site
Three enzymes required to break down lactose RNA
polymerase 3¢ 5¢
Lactose Inactive and sigma
as inducer repressor In presence of inducer factor 5¢ 3¢
Fig. Lac operon model attached at
promotor Sigma factor
Q.2. What is transcription? Explain the process of RNA
Unwinding DNA
polymerase
transcription.
5¢
Ans. Transcription: “The polymerization of RNA molecule 3¢
Initiation
on the DNA template with the help of enzymes and 5¢
Terminator 3¢
same protein factors is termed as transcription”. RNA
site
Synthesis of RNA occurs by polymerization
Sigma factor release
ribonucleotide monomers in 5¢ ® 3¢ direction upon one
3¢ 5¢
of the two DNA strands of a gene called template Elongation
strand. Other strand is called non-template strand. of RNA 5¢ 3¢
Since the base sequence of newly synthesizing RNA
molecule is complementary to that of the template RHO factor
strand. It naturally corresponds to the base sequence of RNA
5¢
3¢
the non template strand of DNA duplex. That is why Termination
of RNA 5¢ 3¢
the non-template strand is called the coding or sense
RNA
strand, whereas the template strand is called the
noncoding or nonsense strand.
RNA RHO factor
Process of Transcription: The whole process of polymerase
transcription is divided into four stages. Fig. DNA to RNA transcription
 64

4. Termination: RNA polymerase will keep Besides undergoing splicing, the pre-mRNA
transcribing until it gets signals to stop. The undergoes distinctive modifications at both ends. At its
process of ending transcription is called 5' end one or two nucleotides are methylated and an
termination, and it happens once the polymerase additional methylated guanosine triphosphate is also
transcribes a sequence of DNA known as liked and serves as a 5' cap. Similarly a 50 to 200
terminators. In prokaryotes 'a' Rho factor binds to adenine containing sequence is added to 3' end and
this sequence and terminate the process and helps in export of the m-RNA into cytoplasm from the
releasing the RNA molecules. nucleus.
Q.3. Give the detailed description of processing of m-RNA Q.4. Mention main steps/stages of DNA replication?
molecules? Or Explain the semi-conservative replication of DNA?
Ans. Processing of m-RNA molecule: In the nuclear DNA Ans. Replication of DNA molecules: The formation of two
of eukaryotic the protein coding genes, from which exact copies of DNA molecules is called replication.
m-RNA are transcribed are known as split genes. The DNA serves as the hereditary blueprint carrying
Because these contain alternating protein-coding the coded informations of all structural and functional
segments called Exons and no protein coding segment characteristics of cells from one to the next generation.
called introns. Hence it is the prime importance before a cell division.
The m-RNA thus transcribed initials known as Amongst all biomolecular only the molecules of DNA
pre-mRNAs, which undergo substance m-RNAs to be possess the unique property of self-duplication.
transported to cytoplasm and translated into proteins. Semi-conservative replication of DNA:
DNA Experimental proof of semi-conservative made of
Transcription
replication was given by Mathew Masson and Franklin
W. Stahl in bacterium Escherichia coli. Watson and
Unstable 5¢ E I E E I E I E E 3¢ Crick discovered the double helical structure of DNA.
HnRNA
Poly A tail
They were the first who proposed the scheme for semi-
7 mGTP cap
End Stabilisation AAAA n conservative replication of DNA. The two
io
yla
t polynucleotide strands of a double stranded DNA are
Ca

5¢ E I E E I E I E E 3¢ en
pp

d
lya anti-parallel and complementary to each-other.
in g

AAAA
Po
Because of the specific pairing of the nitrogenous
RNA splicing
I = Intron bases of the nucleotide monomers of opposite strands
E = Exon
5¢ E I E E I E I E E 3¢ by means of hydrogen bonds join the two strands
Hn RNA AAAA together. Therefore when separated by breaking of the
RNA splicing hydrogen bonds each strands acts as a template or
Spliced RNA AAAA mould upon which a new polynucleotide strand is
E E E E E E
polymerized by complementary pairing of the
3¢ nitrogenous bases of nucleotides. In each of the two
Mature mRNA 5¢
AAAA DNA molecules, thus formed one strand is of the old
7 mGTP cap Poly A tail DNA and the other is the new one. It is because of this
Fig. Overall mechanism of RNA processing feature that the DNA replication is called semi-
(Diagrammatic representation)
conservative.
Process/Mechanism: The process of removing introns The Mechanism of DNA Replication in Eukaryotes:
from pre-mRNA and rejoining the exons together to The mechanism of replication of DNA molecules is
form mature RNA molecule is termed RNA splicing. basically similar in both prokaryotic and eukaryotic
The first step in RNA splicing is to cut the pre m-RNA cells. Yet it was first studied in prokaryotes. British
at 5' and 3' ends of introns to separate all introns and molecular geneticist John Cairns was first to find out
exons from one another. This cutting is catalyzed by the details of DNA replication in E.coli. This process is
spliceosomes which are assembled groups of small quite complex and involves participation of some RNA
RNA-protein complexes each containing once or two and several enzymes.
molecules of small nuclear RNAs (sn RNAs). After
cleavage the exons are rejoined by RNA ligase
enzymes, whereas the introns are degraded.
 65

3'
two-strands of DNA start separating, a Y-shaped
dT C
C A
g stran
Leadin
T G T A replication fork forms. 1968 Huberman and Riggs
C C discovered that the process of replication begins of
A T
T A

two DNA polymerase

C
5' T G both forks and thus proceed in opposite directions

Replisome with
A C G G T C C A A T
Direction of along the DNA molecule. The strands are named as

units
Replication fork movement
of replisome leading and lagging strands.
T G C C A G G T T A
A C 1. As the two strands molecule start separating at a
3' G A T
T A
G G replication fork, a short RNA chain of about to
A C
A T
Laggin
g stra
G T A G complementary ribonucleotide monomers forms
nd
5' opposite each DNA strands using the stars
template.
DNA Polymerase
2. These small RNA molecules are called RNA
3' Primer primers.
C
A C
A T 3. The synthesis of RNA primers is catalyzed by a
G T T A G
trand C C
T
A T
G 5' special type of RNA polymerase called primase
L ea d
ing s A T A C is
5' C T A A G G
s sy nthes enzyme which remains associate with the DNA
A T T
G T nuou
A C G G T C C A Conti
helicase complex.
Okazaki fragment
s 4. The two strands of a DNA molecule are anti-
5' parallel i.e., the direction of one strand is 5'–3' and
T G C C A G G T T A A A T 3'
3'
Laggin
C G
A T T C C T 5'
3'
that of the complementary strand is 3'–5'.
g stra A G G T
A C A
nd G A
C A
T G T
T C 5. The direction of the complementary RNA primer
A G
that forms of 5' end of this strand is obviously 3'–5'
DNA Polymerase Primer
Fig. Replication fork and mechanism of DNA replication
5' from the fork.
6. The direction of RNA primer that forms of 3' end
To make it easier to understand. It can be divided into
of this strand at opposite fork is 5'–3' from the
following steps.
fork.
Decoiling and Recoiling of DNA supercoils:
7. The RNA primer whose 3' end is towards the fork
Molecules of DNA remain condensed or compacted by
the deoxyribonucleotide molecule start linking
super coiling into much shorter chromatin filaments
one behind the other.
than their actual lengths. Their duplication therefore,
8. This linking is catalyzed by DNA polymerase III.
necessitates their step-by-step decoiling in minute
It results into continuous elongation of the newly
segments for synthesis and recoiling just after
forming complementary strand.
synthesis. These process controlled by a special
9. This new strand is, therefore, called the leading
category of enzymes kinds topoisomerases I and II. At
strand.
a specific points, topoisomerase I produces a
10. In case of other RNA primer whose 5' end is
momentary cut in one of the two strands of DNA
towards the fork, deoxyribonucleotide molecules
molecule to uncoil it at this site. The topoisomerase II,
start polymerizing in 5'–3' direction.
also-called DNA gyrase serves the same function, but it
11. This synthesis of new DNA strand with the old
produces a cut in both strands of DNA.
DNA strand cannot occur continuously as the
Unwinding and Melting of DNA Double Helix: replication fork progresses.
Replication of a DNA molecule in eukaryotic cell 12. In 1968 Reiji Okazaki discovered that this new
begins simultaneously at several special sites along the DNA strand is synthesized in small separate
length of the molecule called replication origins. The pieces which are later jointed with each other of
bacterial replication origin is named oric. DNA ligase.
Molecules of certain special types of proteins called 13. This DNA strand is called lagging strand. The
origin-binding proteins, link with a DNA molecule at fragments which are jointed to form it were later
each replication origin. Using the energy of ATP, the named Okazaki fragments.
origin binding proteins now break the H-bonds of the 14. The lagging strand is formed by joining of
two DNA strands. This causes unwinding of the DNA Okazaki fragments, it is necessary to prevent the
ds and separation of its strands of the replication origin. rewinding of DNA helix till these fragments join
This is called melting of DNA molecules. to complete the lagging strand.
Synthesis of New Polynucleotide Chains:
(Bidirectional) As the hydrogen bonds break and then
 66

15. This function is performed by a number of small (a) Cytosine and guanine are attached by three
molecules of single-stranded DNA binding hydrogen bonds.
protein (ssDNA-BP). (b) Adenine and thymine are attached by two
16. Now the DNA polymerase I enzyme removes the hydrogen bonds.
RNA primer one by one replacing these with (v) Diameter of DNA molecule is 20 Å.
deoxyribonucleotides. (vi) In both polynucleotide chains sugar molecules are
17. Ultimately when the adjacent Okazaki fragments placed at 11 Å distance from each other.
remain separated only by minute gaps called (vii) In double helical structure, one complete turn is at
nicks, the enzyme DNA ligase removes these gaps a distance of 34 Å and 10 base pairs are there in a
connecting the fragments with one another. turn.
(viii) DNA nucleus replicates in presence of required
The replication of one strand (leading) is continuous
enzymes in the interphase.
and the other (lagging) is discontinuous i.e., it
(ix) Complementary strands of DNA have
completes in segments. Hence, the replication of DNA
complementary base pairings means if one strand
is semidiscontinuous. has 5¢-3¢ direction of sugar molecules the other
After replication the DNA proof reading mechanism is will have 3¢-5¢ direction.
done by DNA polymerase and DNA ligase enzymes. (x) Ratio of purine and pyrimidine is 1 : 1.
Q.5. Illustrate Watson and Crick’s model of DNA. Explain
its significance. (2017, 18)
Or Make labelled diagram of DNA structure as
proposed by Watson and Crick. (No need of
description) (2016)
Or Describe the structure of double helical DNA model
proposed by Watson and Crick.
Or What is nucleic acid. Explain the double helical
structure of DNA proposed by Watson and Crick.(2020)
Ans. Nucleic acid : Nucleic acid, naturally occurring
chemical compound that is capable of being broken
down to yield phosphoric acid, sugars and a mixture
of organic bases (purines and pyrimidines). Nucleic
acids are the main information-carrying molecules of
the cell, and by directing the process of protein
synthesis, they determine the inherited characteristics
of every living thing. The two main classes of nucleic
acids are deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). DNA is formed by pentose
sugar, phosphoric acid and nitrogenous base.
Nitrogenous bases are of two types : Fig. Double helical structure of DNA

Pyrimidine: It includes cytosine and thymine. Importance/Significance of double helical model in

Purine: It includes adenine and guanine. Sugar Replication of DNA
participating in formation of DNA is deoxyribose (i) At the time of replication both strands separate
sugar. Sugar and phosphate molecules form nucleic and work as template.
acid, whereas bases are attached at their sides. (ii) Sequence of DNA remains same in new cell.
Some important characteristics of DNA are following: (iii) Two DNA segments are synthesised from one
(i) It’s double helical model was first proposed by segment.
Watson and Crick in 1953. (iv) Sequence of nucleotides remains same in
(ii) Both polynucleotide chains are parallel to each complementary strand.
other in double helix of DNA. Q.6. What is genetic code? Give an account of specialities
(iii) Nucleotides attach by phosphate-sugar linkage to of it. (2015, 17, 18)
form polynucleotides. Or What is genetic code? How does it work? (2019)
(iv) Both polynucleotide chains of DNA are Or Write an essay on genetic code. (2019)
connected or linked with each other by hydrogen Ans. Genetic code is the relationship between the sequence
bonds. of nucleotides on mRNA and the sequence of amino
 67

acids in the polypeptide. In 1954, George Gamow, a (ii) Genetic code is unambiguous and specific. Thus,
physicist proposed that in order to code for all the 20 one codon codes for only one amino acid, e. g.,
amino acids, the code should be made up of three CCU codes only for proline and not for any other
nucleotides (triplet code). amino acid.
This can be explained as if one base coded for one (iii) Since, the number of codons is greater, all the
amino acid, only four amino acids could be specified, amino acids, with exceptions of methionine
i. e., the proteins could contain only four amino acids. If (AUG) and tryptophan (UGG); are coded by more
a sequence of two bases coded for one amino acid, the than one codon, a feature referred to as the
four bases could specify only 16 (4×4) amino acids, degeneracy of genetic code, e. g., GGU, GGC,
which is also inadequate. But if a sequence of three GGA and GGG all specify the same amino acid
bases coded for one amino acid, the four bases would glycine.
specify 64 (4×4×4) amino acids. (iv) The codon is read in mRNA in a contiguous
The various features of genetic code which can fashion, i. e., without punctuation. Thus, the code
explained by using the given checker-board are as is commaless.
follows : (v) The genetic code is nearly universal, i. e.,
(i) From all of 64 codons, only 61 code for 20 amino particular codon codes for the same amino acid in
acids and 3 codons (UAA, UGA and UAG) do not all organisms except in mitochondrial codons and
code for any amino acid. Thus, they function as few protozoans.
terminating or stop codons. (vi) AUG is a codon with dual functions. It codes for
the amino acid methionine (met) and also acts as
an initiator codon.

Fig. Triplet codons of mRNA, showing the amino acids which they code
 68

NCERT Fully Solved Exercise

Q.1 Group the following as nitrogenous bases and synthesised from it (DNA or RNA), list the types of
nucleosides: Adenine, Cytidine, Thymine, Guanosine, nucleic acid polymerases.
Uracil and Cytosine. Ans. DNA to DNA (Replication)—DNA dependent DNA
Ans. Nitrogenous bases—Adenine, Thymine, Uracil and polymerase
Cytosine. DNA to RNA (Transcription)—DNA dependent RNA
Nucleoside—Cytidine, Guanosine. polymerase
Q.2 If a double stranded DNA has 20 per cent of cytosine, RNA to DNA (Reverse transcription)—RNA
calculate the per cent of adenine in the DNA. (2020) dependent DNA polymerase
Ans. According to Chargaff’s base pairing rule, amount of Q.7 How did Hershey and Chase differentiate between
cytosine is equal to that of guanine. Similarly amount DNA and protein in their experiment while proving
of thymine is equal to the amount of adenine. that DNA is the genetic material?
So, the given DNA also contains 20 per cent of Ans. Hershey and Chase made use of radioactive (heavy
guanine. isotope) of phosphorus and sulphur. Phosphorus is the
Since, A+T+G+C = 100% and A=T component of DNA (nucleic acid) while sulphur is
So, A+A+20+20 = 100% found in proteins. When such radio-labelled
Or 2A + 40 = 100% bacteriophages were tested for radioactivity, only
Or A = 30% radioactive phosphorus was found in the following
Q.3 If the sequence of one strand of DNA is written as generations. Radioactive sulphur was absent in the
follows: following generations. This proved that only DNA has
5’-ATGCATGCATGCATGCATGCATGCATGC-3’ capacity to get transmitted from one generation to the
Write down the sequence of complementary strand in other.
5 ® 3 direction. Q.8 Differentiate between the followings:
Ans. The sequence of complementary strand in 3’ ® 5’ (a) Repetitive DNA and Satellite DNA
direction would be : (b) mRNA and tRNA
3’-TACG TACG TACG TACG TACG TACG (c) Template strand and Coding strand
TACG-5’ Ans. (a) Repetitive DNA and Satellite DNA : When a
So, the sequence of this strand (complementary strand) small stretch of DNA nucleotides is repeated
in 5’ to 3’ direction would be : many times in a DNA molecule, it is called
5’-GCAT GCAT GCAT GCAT GCAT GCAT repetitive DNA. When DNA is applied to density
GCAT-3’ gradient centrifugation, repetitive DNA appears
Q.4 If the sequence of the coding strand in a transcription in the form of many small peaks one after the
unit is written as follows: other. Such tandemly repeated DNA sequences
5’-ATGCATGCATGCATGCATGCATGCATGC-3’ are called DNA satellites. (So, DNA satellites
Write down the sequence of mRNA. (2019) contain repetitive DNA).
Ans. The coding strand in a transcription unit is the strand (b) mRNA and tRNA : The type of RNA which
which has same base sequence as found in the mRNA conveys message of protein synthesis from DNA
except that it has U in place of T. So, the sequence of to the ribosome, is called mRNA. On the other
mRNA would be : hand, the type of RNA which serves to bring
5’-AUGCAUGCAUGCAUGCAUGCAUGCAUGC-3’ amino acids to the ribosomes, is called tRNA.
Q.5 Which property of DNA double helix led Watson and (c) Template strand and Coding strand : The
Crick to hypothesise semi-conservative mode of DNA strand of DNA double helix which is transcribed,
replication? Explain. i.e., used for the formation of mRNA is called
Ans. DNA double helix has specific base paring. According
template strand. On the other hand, the strand,
to Chargaff, A always pairs up with T and similarly G
which is complementary to the template strand is
pairs up with C and vice versa. This highly specific
base pairing rule, led Watson and Crick to hypothesise called coding strand. (So, coding strand is not
semi-conservative mode of DNA replication. transcribed). It is called so, as it contains the same
Q.6 Depending upon the chemical nature of the template base sequence as found in the mRNA (except that
(DNA or RNA) and the nature of nucleic acids in place of U, it has T).
 69

Q.9 List two essential roles of ribosome during translation. person. So, a person can be identified solely on the
Ans. Two essential roles of ribosome during translation are : basis of the sequence of its nucleotide base pairs.
(a) Bringing charged tRNAs (i.e., tRNA bearing an Therefore the identification of a person on the basis of
amino acid) close to each other its DNA material is called DNA fingerprinting. It is
(b) Forming peptide bond between amino acids to called fingerprinting because earlier for the same
form a polypeptide chain. purpose the fingerprints of the persons were in use.
Q.10 In the medium where E. coli was growing, lactose was Applications of DNA fingerprinting :
added, which induced the lac operon. Then, why does (a) Paternity and maternity : Because a person
lac operon shut down some time after addition of inherits his or her DNA from his or her parents,
lactose in the medium ? DNA sequence patterns (VNTR) can be used to
Ans. This is because of feed back inhibition. When the establish paternity and maternity. The patterns are
lactose related requirements of the E. coli get fulfilled, so specific that a parental DNA sequence pattern
the products of lactose catabolism, inhibit the can be reconstructed even if only the children’s
machinery, i.e., lac operon. DNA sequence (VNTR) patterns are known.
Q.11 Explain (in one or two lines) the function of the (b) Criminal identification and forensics : DNA
followings: isolated from blood, hair, skin cells, or other
(a) Promoter (b) tRNA (c) Exons genetic evidence left at the scene of a crime can be
Ans. (a) Promoter : These are small DNA sequences, compared, through VNTR patterns, with the DNA
which are present near a gene (upstream side). of a criminal suspect to determine guilt or
These regulate the transcription process by innocence.
directing the movement of RNA polymerase, (c) Verification of immigrants : DNA fingerprinting
through the concerned gene. helps to verify whether a hopeful immigrant is (as
(b) tRNA : It is the type of RNA which serves to he/she claims), really close relative of already an
bring amino acids to the ribosomes, during established resident.
translation process. (d) Identification of racial groups: DNA
(c) Exons : These are coding portions of a gene, fingerprinting is also helpful in establishing
which actually carry the information regarding the similarity among different racial groups and thus
formation of a polypeptide chain. helps to rewrite biological evolution.
Q.12 Why is the Human Genome Project called a mega Q.14 Briefly describe the following:
project ? (2020) (a) Transcription (b) Polymorphism
Ans. The Human Genome Project (HGP) is an international (c) Translation (d) Bioinformatics
13-year effort formally begun in October 1990. It was Ans. (a) Transcription : The process of formation of
coordinated by ‘U.S. Department of Energy’ and RNA from a DNA piece is called transcription.
‘National Institute of Health’. It is called a mega This process is the first step in the synthesis of a
project as it aimed at revealing out all hidden facts protein.
about human genome (which contains approximately (b) Polymorphism : Occurrence of a substance in
3 ´ 10 9 base pairs), i.e., number of genes, their many forms is called polymorphism. In humans,
functions, sequencing of whole DNA and genes etc. more than 99.9% of the genome is identical. The
Q.13 What is DNA fingerprinting? Mention its application. difference lies in the remaining 0.1 % DNA. This
(2019, 20) DNA, which is represented by microsatellites
Ans. There are millions of base pairs in our DNA. These shows variable forms (polymorphism), with
base pairs are arranged in specific sequences. Some of regard to number and length.
the nucleotide sequences in two persons may be same (c) Translation : The process of actual assembling of
but not all. DNA of two different persons would amino acids on a ribosome, to synthesise a
definitely have certain differences in the nucleotide polypeptide chain is called translation.
sequences. In other words, the nucleotide sequence of a (d) Bioinformatics : It is a new area of study which
person is highly specific and it does not completely involves the use of living material such as DNA
resemble with the nucleotide sequences of some other and proteins, for data management.
ccc

Note : Due to Covid-19 Chapter-7 (Evolution) is not in the Latest Syllabus 2020-21.
 Unit-3 : Biology in Human Welfare
70
Chapter 7 : EVOLUTION
(This Chapter has been Deleted From Syllabus For Session
2020-21 Due To COVID-19 Epidemic)
Chapter

8
HUMAN HEALTH
AND DISEASE

² Anaemia : It is a condition when the amount of RBCs or parasites are mainly pathogenic, i . e. , they cause certain
haemoglobin in the blood becomes reduced. This condition diseases in their host.
mainly occurs due to iron deficiency. In this condition the ² Vaccine : These are killed antigens, which can produce
oxygen carrying capacity of the blood is adversely affected and antibodies in the body when injected, without causing the
person becomes weak. occurrence of disease. Once the antibodies are produced, the
² Inflammation : The pain in some body parts along with person becomes immune to that particular disease.
swelling is known as inflammation. ² Vector : The organisms, which serve to transmit pathogens or
² Antibiotics : These are drugs which are obtained from certain disease causing substances from one person/place to another
micro-organisms. These may also be prepared artificially. The person/place is known as vector.
antibiotics are effective against various types of bacterial, ² Metabolism : Every living organism carry out certain
protozoan and fungal parasites. bio-chemical reactions in its body, such as production of energy,
² Antibodies : These are specialised types of proteins, present protein’s, digestion etc. Sum total of all these reactions is called
in blood plasma. These are produced by lymphocytes (a type of metabolism.
WBC), in response to some antigenic entry into the body. These ² Immune system : The system that develops immunity in the
serve to kill the antigens. body against foreign invaders, is called immune system. It
² Antigens : These are certain materials or proteins, which includes skin, WBC and their derivatives, various digestive
when enter in the body, stimulate body’s immune system to start juices, saliva and lysozyme etc. Two important components of
producing antibodies. immune system are — (i) Lymphocytes ( B-cells and T-cells) and
² Diarrhoea : The condition of frequent loose motions is known (ii) Tissue macrophages (mature monocytes).
as diarrhoea. It occurs due to food poisoning and infection of ² Innate immunity : Innate immunity refers to all those
gastro-intestinal tract. It results in dehydration and mineral defense mechanisms with which an individual is born and
deficiency in the body. which are always available to protect the living body.
² Eczema : It is a skin disease, which is characterized by ² Antigens : An antigen is any substance which when
redness, patches, itching and burning sensation. In severe cases, introduced in body, stimulates the production of antibodies.
blister formation occurs on the skin. Antigen is essentially a “non-self” material. Antigens are usually
² Edema : It is also known as dropsy. It is a condition when there the proteins, with molecular weight greater than 10,000.
is an excessive accumulation of fluids in the cells, tissues and in ² Hapten : The properties of antigens are due to some
the tissue spaces. This causes a swelling or puffiness of tissue. non-proteineous, low molecular weight substances, called
² Immune system : Our body bears a unique system that fights hapten. Haptens are better called antigenic determinants. These
against various types of pathogens and foreign substances and are closely associated with protein part of the antigen. Hapten
prevents our body from their harmful effects. This system is determines the specificity of antigen but alone can not stimulate
called immune system. the immune response.
² Necrosis : The decay of tissues is known as necrosis. It occurs ² HLA : HLA stands for human leukocyte antigen. It is an antigen,
in many diseases, especially in tuberculosis. which is produced by MHC. It helps in the recognition of self
² Parasite : The organisms, which live at the cost of other and non-self.
organisms, are called parasite. The victim is called host. The ² MHC : MHC (Major histo-compatibility complex) is a gene,
which produces MHC antigens (In humans the MHC antigen is
 71

also known as HLA). It is present on the short arm of 6th human ² Humoral immunity : The antibody mediated immunity, is
chromosome. called humoral immunity.
² Antibodies : These are immunoglobulin (gamma globulin) ² Cellular immunity : The cell mediated immunity, which is
molecules, which are formed by plasma cells (a derivative of formed by activated T-lymphocytes, is called cellular immunity.
B-Lymphocytes), in response to an antigen. These destroy the ² Opsonisation : Opsonisation refers to the coating of (bacteria
antigens or coat them for subsequent phagocytosis. Antibodies or antigens) by antibodies to facilitate their subsequent
form humoral immunity. Five major types of antibodies are – phagocytosis.
IgG, IgM, IgA, IgE and IgD. ² Vaccination : It is the process of introducing a preparation of
² Lymphocytes : Lymphocytes are specialised WBC cells, which antigenic proteins or pathogens (inactivated/attenuated
like other blood cells born in bone marrow, but are later pathogens) into the body, to generate the primary immune
transferred to lymph glands (thymus, tonsil, spleen etc) for response.
further maturation. Bone marrow contains certain primordial ² Allergy : Allergy is the inappropriate and excessive
stem cells, which are of two types — B-cells and T-cells. (hypersensitive) immune response to some common antigens.
² Interferons : These are a class of glycoproteins, released in a ² Autoimmune diseases : Autoimmune diseases are those
small amount by the cells, when infected with a virus. disorders, which are caused when the body’s immune system
Interferons are therefore secreted only in response to some viral goes off the track and starts destroying body’s own cells and
infection. molecules.

Multiple Choice Questions 1 Mark

Q.1. Athlete’s foot is caused by : Q. 9. Interferons are :

(a) Tinea pedis (b) Tinea capitis (a) Anti-bacterial protein (b) Anti-viral protein
(c) Candida albicans (d) Rickettsia (c) Complex protein (d) Anti-clotting protein
Q. 2. Hepatitis B virus is a: Q.10. BCG Vaccine is given against : (2017)
(a) Hepadna virus (b) Variola virus (a) Typhoid (b) Cholera
(c) Retro virus (d) Picorna virus (c) TB (d) Diphtheria
Q.3. Immunoglobulins serving as mediators in allergic Q.11. Aedes aegypti is a vector of : (2017)
response are: (a) Dengue fever (b) Malaria fever
(a) IgE (b) IgD (c) Filariasis (d) Kala-azar
(c) IgM (d) IgA Q.12. Which of the following disease is not produced by
Q. 4. The cell-mediated immunity inside the human body is virus?
carried out by : (a) Polio (b) T.B.
(a) B-lymphocytes (b) Thrombocytes (c) AIDS (d) Chicken pox
(c) Erythrocytes (d) T-lymphocytes Q.13. Which occur in antiserum ? (2018)
Q. 5. Which stage of plasmodium is infective to man ? (a) Antigen (b) WBCs
(a) Trophozoite (b) Sporozoite (c) Antibody (d) RBCs
(c) Gametocyte (d) Cryptomerozoites Q.14. Morphin is obtain from poppy : (2018)
Q.6. Which of the following is a bacteriogenic disease? (a) Pome (b) Alkaloids
(2014) (c) Latex (d) Tennin
(a) Polio (b) Pyro's disease Q.15. Who was discovered penicilin? (2018)
(c) Diarrhoea (d) Elephantiasis (a) Weisman (b) Smith
Q.7. The vector of chickungunya virus is : (2017) (c) Fleming (d) Arburh
(a) Culex (b) Aedes Q.16. Which of the following disease is confirmed by widol
(c) Anopheles (d) None of these test? (2020)
Q. 8. Sleeping sickness is caused by which organism? (a) Typhoid (b) Malaria
(2015) (c) Dysentery (d) Filaria
(a) Euglena (b) Plasmodium
(c) Tryponosoma (d) Amoeba
 72

Answers
1. (a) 2. (a) 3. (a) 4. (d) 5. (b) 6. (c) 7. (b) 8. (c) 9. (b) 10. (c)
11. (a) 12. (b) 13. (a) 14. (c) 15. (c) 16. (a)

Very Short Answer Type Questions 1 Mark

Q.1. What is health? Q.12. Writes names of pathogens and their carriers of
Ans. Health is a state of complete physical, mental and following diseases (2015)
social well being and not merely the absence of disease Filariasis, Malaria dengue.
or infirmity. Ans. Disease Pathogen Carrier
Q.2. Name the causative agent of malaria? (2016) Filaria Wuchereria Female Culex
Ans. The causative agent of malaria is a protozoan parasite Malaria Plasmodium Female Anopheles
named plasmodium. Dengue Virus Female Aedes
Q.3. Who is the father of Immunization? Q.13. Name few disease which show hallucinating
Ans. Edward Jenner symptoms. (2017)
Q.4. What are interferons? (2015, 16, 17) Ans. Hallucination is a perception in the absence of external
Ans. Virus infected cells secrete proteins called interferons stimulus. Hallucination, happens during
which protect non-infected cells from further viral schizophrenia, formication, etc.
infection. Q.14. Make well-labelled diagram of the structure of
Q.5. Name the pathogens of tuberculosis, cholera and sporozoite of Plasmodium under electron microscope.
AIDS. (2018)
Ans. The pathogens of these diseases are : Ans.
Secretory
Tuberculosis — Mycobacterium tuberculosis Mitochondrion Nucleus organelles
Cholera — Vibrio cholerae Microtubules
AIDS — HIV Apical cap

Q.6. Mention the useful as well as the harmful drug Endoplasmic Convoluted tubules
obtained from the latex of poppy plant. reticulum Micropyle
Pellicle
Ans. Useful drug — morphine
Fig. Structure of a sporozoite (infective stage) of Plasmodium
Harmful drug — heroin
Q.7. Name the host cells which are mainly affected by HIV. Q.15. Which is cause of diarrhoea disease in human? (2018)
Ans. T4 lymphocytes are the host cells affect by HIV. Ans. Salmonella and E.coli
Q.16. Name two viruses causes common cold in man. (2018)
Q.8. Name any two types of cells that act as cellular barriers Ans. Rhinovirus and corona virus.
to provided innate immunity in humans?
Q.17. Where is the formation and maturation of T and
Ans. Leucocytes (WBC) and natural killer in the blood are
B-lymphocytes. (2018)
two types of cells that act as cellular barriers to provide
Ans. Formation of both T and B-lymphocytes in bone
innate immunity in humans.
marrow. Maturation of T-lymphocytes in thymus gland
Q.9. Breast fed babies are more immune to disease than the
and B-lymphocytes in bone marrow.
bottle fed babies. Why? (2017)
Q.18. What is immunity? (2019)
Ans. Breast fed babies get some antibodies from their
Ans. The ability of the body (host) to fight against the
mother through the milk thus they are immunised.
disease causing agents is called immunity. It is of two
Q.10. Describe in brief bad effects, prevention and cure of types—innate immunity and acquired immunity.
alcoholism? (2017) Q.19. Which organism cause the typhoid fever? (2020)
Ans. Alcoholism affects the function of liver, nervous Ans. Typhoid is caused by bacterium Salmonella typhi.
system, stomach, heart, kidney etc. It can be cure
Q.20. Which disease born by Entamoeba? How can it
rehabilitation technique.
controlled? (2020)
Q.11. Name the plant source of ganja? How does it affect the
Ans. Entamoeba is the cause of amoebic dysentery.
body of abuses?
Preventive measure : Boil water or treat with iodine
Ans. Cannabis sativa. It damages cardio-vascular system.
tablets.
Avoid eating street foods.
Avoid raw vegetables when in endemic areas.
 73

Short Answer Type Questions 2 & 3 Marks

Q.1. Differentiate between active immunity and passive Each antibody molecules has four peptide chains.
immunity. (2009, 10, 11, 12, 18) Chemically they are glycoproteins, called
Or Differentiate between active immunity and passive immunoglobulin and represented as Ig. Each Ig
immunity and give one example of each. (2020) molecule is said to be made of two heavy chains and
Ans. Difference between active and passive immunity two light chains. These are arranged in a Y-shaped
Active immunity Passive immunity configuration. Stem of Y is exclusively made up of
1. It develop when a host Antigens are not directly heavy chains but the arms are made up both light and
is exposed to antigens. introduced in the host. heavy chains. On the tip of each arm of antibody there
2. Antibodies are Ready-made antibodies is an antigen binding fragment which holds antigen
produced in the host are directly given to host. polypeptide chains of antibody are bound together by
body. disulphide bond and no covalent bonds.
3. Active immunity is Passive immunity to faster Q.4. How many types of antibodies are found? Give the
slow. than active immunity.
function of each?
4. It produce immunity Immunity works for that Ans. Types of Antibodies: Antibodies are classified into
for long time. time, not for long.
five major types.
5. Example—antibodies Example—Antibodies 1. Immunoglobulin G(IgG) : It is smallest and most
that develop in a given to a person to
person’s own immune prevent to disease or to abundant (80%) antibody made up of single
system after the body is treat disease after the body monomer unit. It is only Ig that transferred across
exposed to an antigen is exposed to an antigen. the placenta from mother to foetus. This gives
through a disease. some protection to unborn children from diseases.
Q.2. Differentiate between innate and acquired immunity. This is effective against bacteria virus and fungi.
(2010, 20) 2. Immunoglobulin A (IgA): IgA is commonly
Ans. Difference between innate and acquired immunity called as secretory antibody. It is made up of two
Innate immunity Acquired immunity monomers. It occurs in tears, sweat, saliva and
1. Innate immunity is It is pathogen specific. breast milk (colostrum). A lack of IgA often
non-specific. causes major infections of mucosal surfaces such
2. It is present since It is produced in response as mouth, throat and lungs.
birth. to an antigen or pathogens 3. Immunoglobulin M(IgM): It is made up of five
3. It is not characterized It is characterized by monomer units. It is strong activator of the
by memory. memory. complement cascade.
4. Innate immunity Barrier system is absent. 4. Immunoglobulin E(IgE) : The main action of it is
consists of barriers.
binding to and activating mast cells, which causes
5. Example—cough Example—The placental
reflex, enzyme in transfer of IgG from
swelling, redness, pain and itching effects.
tears and skin oils. mother to foetus during 5. Immunoglobulin D(Ig D): It serves as receptors at
pregnancy. the surface of B cells to secrete other antibodies.
Q.3. Comment on Antibodies? (2014, 20) Q. 5. What is vaccination? (2010)
Ans. Antibody: Antibodies are proteins that have the ability Ans. Vaccination : The process of giving vaccines is called
to bind antigens. vaccination. Vaccines are preparations of antigenic
Antigen binding site proteins of pathogen or inactivated/weakened
N
Antigen S
S S
S pathogens. The antibodies produced in the body
binding site
against these antigens would neutralize the pathogenic
S S
S
S
S S
S
S agents during actual infection. The principle of
S
S S
S
vaccination is based on the property of ‘memory’ of the
S S
S
S S
S S
S immune system. B and T cells that recognize the
Light chain
S S
pathogen quickly on subsequent exposure and
S S
overwhelm the invadens with a massive production of
Heavy chain antibodies.
S S
S S Q.6. Write short note on allergies.
C C
Ans. The exaggerated response of immune system to certain
Fig. Structure of an antibody molecule antigens present in the environment is called allergy.
 74

The substances to which such an immune response is Q.9. Write short note on any one. (2018)
produced are called allergens. The antibodies produced (a) Cancer (b) Malaria
to these are of the IgE type. Common types of allergens Ans. See for cancer Long answer type Q.No. 1
are mites in dust, pollens, animal dander etc. See for malaria Short answer type question-13.
Allergy is due to the release of chemicals like Q.10. What is immunity? Explain the mechanism of acquired
histamine and serotonin from the mast cells. immunity? (2019)
Symptoms: Allergy symptoms can be categorised as Ans. Please see the answer of Long answer question-7.
mild, moderate or severe symptoms. Allergy symptoms Q.11. Write short notes on the following :
include sneezing, watery eyes, running nose and (i) Elephantiasis (ii) Ascariasis
difficulty in breathing. Or Write a short note on Filariasis (Elephantiasis).
Q. 7. Write a short note on dengue fever. (2017, 18) (2020)
Ans. Dengue hemorrhagic fever is a more serious form of Ans. (i) Elephantiasis : Please see ans of Long answer
dengue infection. It is caused by four dengue fever type question-1
virus (DEN 1, DEN 2, DEN 3 and DEN 4). Dengue (ii) Ascariasis : This disease spreads by helminth
viruses are transmitted by the bite of an infected Aedes parasite—Ascaris lumbricoides, which is an
mosquito. internal parasite. It is transmitted through
Symptoms : Symptoms appear three to 15 days after contaminated water, fruits and vegetable etc.
the mosquito bite and include high fever and severe Symptoms : Internal bleeding, anaemia, fever,
headache. Other symptoms are joint pain, muscle and blockage of intestinal passage and muscular paint etc.
bone pain, rash and mild bleeding. are its symptoms.
Prevention : The Aedes mosquito breeds in stagnant Prevention and Treatment : Keeping clean
water bodies like water tanks, coolers etc. The disease environment, no open disposal of faeces, no
can be prevented by eliminating breeding places of consumption of polluted food and rotten fruits and
mosquitoes. vegetables, proper washing of hands before eating,
Q. 8. Write the causative agent, symptoms and treatment of proper cleanliness of toilets and use of pure water, etc.,
swine flu and Chikungunya. are few preventive measures of this disease. On the
Ans. Swine flu: occurrence of disease, piperazin citrate and piperazin
Causative agent: Swine flu is a respiratory disease phosphate, etc., medicines are used to kill the parasite.
caused by influenza virus (RNA) named, novel HINI. Q.12. Differentiate between the following and give one
The newest swine flu virus is influenza AH3N2V. example of each : (2019)
Symptoms: Fever, cough, nasal secretions, fatigue and (i) Innate and acquired immunity
headache. The most serious complication of the flu is (ii) Active and passive immunity
pneumonia. Ans. Please see the ans of Short answer type question-2 and
Prevention and treatment: Vaccination is the best way 1.
to prevent or reduce the chances of becoming infected. Q.13. Write pathogenicity, symptoms and preventive
Two antiviral agents, Zanamivir (Relenza) and measures of malaria. (2019)
Oscltamivir (Tamiflu), have been reported to help Or How is malaria disease transmitted? Mention its
prevent or reduce the effects of swine flu when it taken control measures. (2019)
within 48 hours of the onset of symptoms. Or Which are the different species of Plasmodium?
Chikungunya : Explain the different types of malaria caused by thein.
Causative agent : It is caused by an RNA virus that (2020)
belongs to the alpha virus genus. Ans. Malaria : About 300 million people are infected with
Symptoms: Chikungunya is characterized by an abrupt malaria every year and more than 2 million die
onset of fever frequently with joint pain. Other annually due to malaria.
common signs include muscle pain, headache, nausea, Pathogenicity :
fatigue and rash. (i) Malaria is caused by a protozoan parasite, named
Prevention and treatment: Prevention and control relies as Plasmodium.
heavily on reducing the number of natural and artificial (ii) Its four species are known—P. falsiparum, P.
water filled container habitats that support breeding of vivex, P. malarie and P. ovale.
the mosquito. (iii) The infective stage of Plasmodium lives in the
There is no specific antiviral drug treatment for salivary glands of female Anopheles.
chikungunya.
 75

(iv) When this insect sucks the blood of a normal man, chemicals like histamine and serotonin from the
the Plasmodium reaches into the blood and results mast cells.
in malaria. (Note: male Anopheles is Autoimmune disease : Sometimes, due to genetic
non-infective as it feeds on plant juice). and other unknown reasons, the body attacks
Symptoms : self-cells. This results in damage to the body and
(i) Headache, nausea, muscular pains and high fever is called autoimmune disease. Rheumatoid
are the main symptoms of malaria. arthritis which affects many people in our society
(ii) Each malarial attack is of 6-10 hours and consists is an autoimmune disease.
of three stages — cold stage (feeling very cold and Q.15. Give an account on misuse of drugs and alcohols
shivering), hot stage (high fever, faster respiration during adolescence. (2019)
and heart beat) and sweating stage (in which Ans. Misuse of drugs and alcohols during adolescence :
temperature goes down to normal). Curiosity, need for adventure and excitement and
(iii) When the patient gets cured of malaria, the patient experimentation, constitute are the most common
becomes weak and anaemic. Malaria may also causes, which motivate youngesters towards drugs and
cause the enlargement of spleen and liver. alcohol use.
Prevention : Following measures may be taken to The first use of drugs or alcohol is generally because of
prevent malaria : curiosity and experimentation, but later the child starts
(i) Use wire-gauze on doors and windows to prevent developing an addiction for the alcohol/drugs. Stress
entry of mosquitoes. and some social pressure also play a significant role in
(ii) Use insect-repellents to prevent mosquito- bite. compelling youngesters to try alcohol and drugs.
(iii) Sleep under mosquito net. Television, movies, newspapers, internet also help
(iv) Mosquito larvae should be killed by sprinkling significantly to promote their inclination towards
kerosene oil on large sized water bodies. cigarette smoking and tobacco chewing. Family
(v) Larvivorous fishes such as Gambusia, minnows atmosphere is also one the major causes.
and trouts etc. (which feed on mosquito larvae) Q.16. Define cancer and comment upon its various types.
may be introduced into water bodies. Similarly (2019)
ducks can also control the larval population of Ans. Please see Long anwer type question-1.
insect. Q.17. Describe in brief the harmful effects caused by misuse
(vi) Kill adult mosquitoes by spraying insecticides. of alcohol. (2019)
(vii) Destroy mosquito-breeding places. Ans. Please see NCERT exercise question-14.
(viii) Fill up all ditches with soil to avoid any Q.18. Write the causal organisms and control measure of
accumulation of water. Dengue and Chikungunya. (2019)
Control: Quinine (a drug, extracted from the bark of Ans. Dengue : Please see the answer of Short answer type
Cinchona calisaya tree) is known to be highly effective question-7.
in treating malaria. Chikungunya : Please see the ans of Short answer type
Q.14. Differentiate between the following : (2019, 20) question-8.
(i) Physical barrier and cellular barrier Q.19. Write a short note on opioids. (2020)
(ii) Allergy and autoimmune disease. Ans. Opioids are substances that, when reaching opioid
Ans. (i) Physical barriers : Skin on our body is the main receptors, have effects similar to those of morphine.
barrier which prevents entry of the Medically they are primarily used for pain relief,
microorganisms. Mucus coating of the epithelium including anesthesia. Other medical uses include
lining the respiratory, gastrointestinal and suppression of diarrhoea, replacement therapy for
urogenital tracts also help in trapping microbes opioid use disorder, reversing opioid overdose,
entering our body. suppressing cough. Extremely potent opioids such as
Cellular barriers : Certain types of leukocytes carfentanil are approved only for veterinary use.
(WBC) of our body like Polymorpho-Nuclear Opioids are frequently used non-medically for their
Leukocytes (PMNL-neutrophils). euphoric effects.
(ii) Allergy : The exaggerated response of the Side effects of opioids may include itchiness, sedation,
immune system to certain anitgens present in the nausea, respiratory depression, euphoria and
environment is called allergy. The substances to constipation. Opioids act by binding to opioid
which such an immune response is produced are receptors. They are found principally in the central and
called allergens. Allergy is due to the release of peripheral nervous system and the gastrointestinal
 76

tract. These receptors mediate both the psychoactive Q.22. What is pathogen? Write down the names of pathogens
and the somatic effects of opioids. causing typhoid fever and common cold in man and
Q.20. Write a short note on human disease caused by also symptoms of these disease. (2020)
mosquitoes and their control. (2020) Ans. Pathogen : A pathogen or infectious agent is a
Or Write the names of any two pathogens causing biological agent that cause diseases or illness to its
diseases in humans and comment upon their regulation. host. The term is most often used for agents that
(2020) disrupts the normal physiology of multicellular animal
Ans. The diseases caused by mosquitoes are malaria, dengue or plant. However pathogens can infect unicellular
and chikungunya. organisms from all of the biological kingdoms.
Malaria : See the answer of Short answer question-13. Common cold : See the answer of L.A. question-3.
Dengue : See the answer of Short answer question-7. Typhoid fever—
Chikungunya : See the answer of Short answer Cause : Typhoid fever is caused by Salmonella typhi. It
question-8. is rare in industrialized countries. However it remains a
Q.21. Draw a labelled diagram of life cycle of malaria serious health threat in the developing world,
parasite. (2020) especially for children.
Ans. Spreading : Typhoid fever spreads through
When the mosquito bites
another human, sporozoites contaminated food and water or through close contact
are injected with bite
into host’s body. with some one who is infected.
Mature infective stages Signs and symptoms : Signs and symptoms usually
(sporozoites) escape Parasites (sporozoites)
from intestine and Sporozoites reach the liver through include a high fever, headache, abdominal pain and
migrate to the mosquito blood.
salivary glands.
Salivary glands
Liver
either constipation or diarrhoea.
Fertilisation and
Mosquito Host Most people with typhoid fever feel better within a few
(sexual)
development take
The parasite reproduces days of starting antibiotic treatment, although a small
place in the
asexually in liver cells,
mosquito’s stomach.
bursting the cell and
number of them may die of complications. Vaccines
es Human Host
cyt releasing its gametes against typhoid fever are available, but they are only
Female mosquito meto (asexual)
into the blood.
takes up gametocytes Ga
with blood meal.
Female
Parasites reproduce asexually partially effective.
Male in red blood cells, bursting the
red blood cells and causing
Sexual stages (gametocytes) cycles of fever and other
develop in red blood cells. symptoms. Released parasites
Stages in the life cycle ofPlasmodium infect new red blood cells.

Long Answer Type Questions 5 Marks

Q.1. What do you understand by infectious and non- Symptoms: The disease is characterized by
infectious diseases? Write their pathogens symptoms constipation, abdominal pain and cramps, stool
and preventive measures by giving two examples of with excess mucous and blood clots.
each. (2014) Transmission: Houseflies are the mechanical
Or What is diabetes mellitus disease? Write two main carriers of the pathogen and serve to transmit the
symptoms of this disease. (2013) parasite from faeces of infected person to food.
Ans. (a) Infectious or communicable diseases: Those Thus contaminated food and water are the main
diseases which can pass from one infected person to a sources of infection.
healthy one by various means are called infectious Preventive measures : (i) Throughly wash fruits
diseases. A wide range of organism like bacteria, and vegetables before eating. (ii) Avoid eating
viruses, fungi, and protozoa, helminthes could cause foods or vegetables unless you wash and peel the
disease in men. yourself. (iii) Stick to bottled water and soft
Some infectious diseases are : Typhoid fever, drinks. (iv) If you must drink water, boil it or heat
pneumonia, common cold, malaria, amoebiasis, it with iodine.
ascariasis, filariasis etc. (ii) Elephantiasis (Filariasis) : Wuchereria is a
(i) Amoebiasis (amoebic dysentery) : Entamoeba parasitic roundworm spread by a mosquito vector.
histolytica is a monogenetic protozoan parasite. It It causes lymphatic filariasis. Two species,
occurs in the large intestine of human and causes W.bancrofti and W.malayi are common to infect
amoebiasis.
 77

man. If infection is left untreated, it can develop Q.2. Describe harmful effects caused by the following and
into a chronic disease called elephantiasis. also mention their prevention measures. (2014, 17)
Symptoms: Filarial worms cause a slowly (a) Alcohol
developing inflammation of the organs in which (b) Drugs (intoxicating medicines)
they live usually the lymphatic vessel of the lower (c) Tobacco
limbs and the disease is called filariasis. The Ans. (a) Harmful effects of alcohol : Some harmful
genital organs are also often affected. effects of alcohol are as following :
Preventive measures : Mosquitoes breeding (i) Instant adverse effects of alcohol/drugs are
places should be destroyed to prevent this disease. expressed in the form of indiscriminates
Hetrazan, antimony and arsenic compounds are behaviour, vandalism and violence.
used as its cure. (ii) Consuming high quantity of these can cause
(b) Non-infectious diseases: These diseases are not respiratory failure, heart failure and even death
transmitted from one person to other. These occurs due due to cerebral hemorrhage. First unconscious-
to deficiency of any nutrient substances or due to ness then coma then death.
sensitivity for substance or metabolic defects. Such as (iii) Academic and social life is affected by use of
diabetes, heart disease, arthritis, cancer etc. alcohol/drug. Absence from school/college
(i) Diabetes: This is an ancient human disease, without any clear reason, lack of interest in
which is caused due to deficiency of insulin as a personal hygiene, loneliness, depression,
result of slow activity of b-cells of pancreas. rebellious behaviour, deterioration relationship
Glucose level increase in blood of affected person with family and friends, changes in the sleeping
and is excretes with urine. and eating habits, hesitance in hunger and weight
Symptoms : The patient gets weakness. etc.
♦ Weight starts decreasing. (iv) Persons consuming alcohol during lack of money,
♦ Tiredness occurs. starts to resort to theft.
♦ Urine comes frequently. (v) Persons who take drugs intravenously, have more
Prevention : 1. Sugar containing substances possibilities to get serious infections like AIDS
should not be used in food. and hepatitis-B.
2. Regular exercise should be done. (vi) Consuming drugs and alcohol during pregnancy
cause adverse effect on foetus.
(ii) Cancer: This disease occurs due to uncontrolled
(vii) Physical characters start changing in males and
division of body cells because of activation of
females.
oncogenes present in the cells. Some substances
(b) Harmful effects of drugs :
are helpful to produce cancer; these are called
(i) Drugs impose adverse effects on nervous system
carcinogens.
and person becomes dependent on them. These
Causes of cancer
© Radiation that can penetrate to the nucleus.
drugs are called intoxicating drugs. These drugs
© Tobacco chewing causes mouth cancer. are also called psychotropic drugs. e.g., Cannabis,
© Smoking causes mouth, throat, and pharynx and hemp, hashish, etc.
lung cancer. (ii) When a person is constantly dependent on taking
Types of cancer : These are of two types— a drug, then that state is called drug addiction.
© Benign remain confined to their original location Such person becomes physically and mentally
and do not spread in the entire body. sick for that drug.
© Malignant are the mass of proliferating cells, (iii) Drug addicted person, feels lively and healthy
called neoplastic or tumour cells. These grow after using these drugs.
rapidly invade and damage the surrounding normal (c) Harmful effects of tobacco : Generally people
cells. use tobacco in the form of cigarette, beedi,
Symptoms: Sharp rise in any wart of body. hookah, etc. Its uses cause many adverse effects
© Formation of tumour in any part. on human body. In children, their effects are fast,
© Regular loss of weight. but slowly in adults. Hence, children and adults
Treatment : should avoid its consumption.
© Keeping away from radiations and pollutants can (i) Nicotine, the drug that makes tobacco addictive,
prevent cancer. goes to your brain. It makes you feel good when
© Radio therapy. you are smoking, but it can make you anxious,
© Chemotherapy.
78

nervous, moody and depressed after you smoke. teacher in the best interest of the person
Using tobacco also can cause headaches and concerned. Appropriate measures would then be
dizziness. required to diagnose the malady and the
(ii) Tobacco stains your teeth and gives you bad underlying causes. This would help in initiating
breath. Tobacco ruins some of your taste buds, so proper remedial steps or treatment.
you won’t be able to taste your favorite foods as (v) Seeking professional and medical help : A lot of
well. help is available in the form of highly qualified
(iii) Smoking increases your heart rate and blood psychologists, psychiatrists, and de-addiction and
pressure. If you try to do activities like exercise or rehabilitation programmes to help individuals
play sports, your heart has to work harder to keep who have unfortunately got in the quagmire of
up. drug/alcohol abuse. With such help, the affected
(iv) Smokers have trouble breathing because smoking idnividual with sufficient efforts and will power,
damages the lungs. If you have asthma, you can can get rid of the problem completely and lead a
have more frequent and more serious attacks. perfectly normal and healthy life.
Smoking causes a lot of coughing with phlegm Q. 3. What is disease? Explain the various types of diseases
(mucous). Tobacco can also increase emphysema caused by viruses and nematodes and their control
(lung disease) and lung cancer. measures. (2017)
(v) Smoking causes dry, yellow skin and wrinkles. Ans. The condition of improper functioning or any
The smell sticks to your skin too. condition which interferes with the normal functioning
Prevention and Control : The age-old adage of of one or more organs or systems of the body and
‘prevention is better than cure’ holds true here also. It is causes disorder of mind or body is called diseases. It is
also true that habits such as smoking, taking drug or characterized by various signs and symptoms.
alcohol are more likely to be taken up at a young age, Various types of diseases caused by viruses are given
more during adolescence. Some of the measures below :
mentioned here would be particularly useful for (i) Common cold: Causative agents of common cold
prevention and control of alcohol and drugs abuse are rhinoviruses. It is the most common viral
among adolescents. infection found in case of humans. These viruses
(i) Avoid undue peer pressure : Every child has majorly affects the nose and the respiratory
his/her own choice and personality, which should passage, (but not the lungs).
be respected and nurtured. A child should not be Symptoms : Include nasal congestion and
pushed unduly to perform beyond his/her discharge, sore throat, hoarseness, cough,
threshold limits; be it studies, sports or other headache, tiredness, etc. Symptoms usually last
activities. for 3-7 days. Infection is transmitted through
(ii) Educationa nd counselling : Educating and droplets resulting from coughing or sneezes of an
counselling him/her to face problems and stresses, infected person or through contaminated objects
and to accept disappointments and failures as a such as pens, books, cups, door knobs, computers
part of life. It would also be worthwhile to keyboard, etc.
channelise the child’s energy into healthy pursuits Control measures : (i) Avoid touching your eyes,
like sports, reading, music, yoga and other nose and mouth with unwahsed hands. Viruses
extracurricular activites. that cause colds can enter yourbody this way and
(iii) Seeking help from parents and peers : Help from make you sick. (ii) Stay away from people who
parents and peers should be sought immediately are sick.
so that they can guide appropriately. Help may (ii) AIDS : It’s pathogen is Human Immunodefi-
even be sought from close and trusted friends. ciency Virus (HIV). It destroys T-helper
Besides getting proper advise to sort out their lymphocytes and weakens immune system, which
problems, this would help young to vent their causes many diseases to accumulate inside the
feelings of anxiety and guilt. body. It has no treatment till date. It spreads
(iv) Looking for danger signs : Alert parents and through infected needle, blood donation, sexual
teachers need to look for identify the danger signs contacts, etc.
discussed above. Even friends, if they find Prevention and control : Blood banks should be
someone using drugs or alcohol, should not screened for HIV, use of disposable needles and
hesitate to bring this to the notice of parents or
 79

syringes, use condoms during coitus and promote of blastocysts and adult stem cells which are
regular checkup for HIV. found in various tissues.
Various types of diseases caused by nematodes (iii) Health: According to World Health Organisation
are given below. (WHO), health is a state of complete physical,
(a) Ascariasis—This disease spreads by mental and social well being and not merely the
helminth parasite—Ascaris lumbricoides absence of disease or infirmity. Healthy people
(unhostile), which is an intestinal parasite. It are more efficient at work which helps in
is trasmitted through contaminated water, increasing the productivity and brings economic
vegetables, fruits, etc. prosperity. It also increases the longevity of
Symptoms are internal bleeding, muscular people by reducing infant and maternal mortality
pain, fever, anaemia and blockage of rates.
intestinal passage. Health is mainly affected by :
Prevention and Treatment : Keeping clean (a) Genetic disorders which the child inherits from
environment, no open disposal of faeces, no parents by birth and deficiencies with which a
consumption of polluted food and rotten child is born.
fruits and vegetables, proper washing of (b) Infections caused by pathogens.
hands before eating, proper cleanliness of (c) Lifestyle including the food and water we take,
toilets and use of pure water, etc., are few rest and exercise, habits that we have or lack, etc.
preventive measures of this disease. On the Good health can be achieved and maintained by :
occurrence of disease, piperazin citrate and (a) Balanced diet, personal hygiene and regular
piperazin phosphate, etc., medicines are used exercise.
to kill the parasite. (b) Regular yoga practice to achieve physical and
(b) Filariasis : See Long answer type Q.No. 1 mental health.
Q.4. Write short notes on any two of the following. (2017) (c) Awareness about the diseases and their effects on
(i) Alcohol abuse different body functions.
(ii) Stem cell (d) Vaccination (immunisation) against infectious
(iii) Human health diseases.
Ans. (i) Alcohol abuse : Ethyl alcohol or ethanol (e) Proper disposal of wastes, control of vectors,
(C 2 H 5 OH) is a colourless liquid produced by the maintenance of hygenic food and water resources.
fermentation of carbohydrates. Q.5. What is called drug addiction? Mention effects of
Alcohol causes intoxication and, therefore it can intoxicating drugs. (2016)
as slow poison. The drinker begins with small Or What is addiction? Give the name of main
doses and then slowly starts consuming large intoxicating drugs and explain their effects. (2020)
doses and became addicts. Alcohol addicts are Ans. When a person is constantly dependent on taking
called alcoholics. drugs, then this state is called drug addiction. Such
Stress and some social pressure also play a person becomes physically or mentally sick for that
significant role in compelling youngesters to try drugs. Drug addicted person feels lively and healthy
alcohol. after using that drug.
The immediate effects of alcohol abuse are Types of intoxicating/narcotic drugs : Intoxicating
observed in the form of reckless behaviour, drugs can be categorised in following groups—
vandalism and violence. (i) Tranquiliser and hypnotics: These drugs affect
Most common warning signs of alcohol abuse: central nervous system. Reduce tension and
(a) Drop in academic performance. anxiety of the brain and induce sleep, e.g., balium,
(b) Change in sleeping and eating habits. librium, barbiturates, equanil, etc.
(c) Loss of interest in hobbies. (ii) Stimulants or antidepressants: These drugs also
(d) Aggressive and rebellious behaviour. affect central nervous system. They get relief
(ii) Stem cell: These are undifferentiated biological from pain. Blood pressure increases and
cells that can differentiate into specialized cells behaviour becomes violent, e.g., tofranil,
and can divide to produce more stem cells. They caffeine, amphietamines, methamphetamines,
are found in multicellular organisms. In mammals etc., tea, coffee cocoa also come under these.
there are two types of stem cells; embryonic stem (iii) Hallucinogens or Psychedelic: They produce
cells, which are isolated from the inner cell mass vision and auditory illusions. This is the drug
 80

altering thoughts and feelings, e.g., cannabis, through the air by droplets that escape when an
hemp, hashish, marijuana, charas, LSD, infected person coughs, sneezes or talks.
mescaline, psilocybin, etc. Indirectly from an infected person. In rare instances,
(iv) Opiates: They reduce pain, anxiety and tension. airborne virus can spread farther, possibly through the
Reduce blood pressure and respiration rate. They ventilation system in a building, infecting people in
induce sloth and sleep. An opiate is a group of other rooms or on other floors.
narcotic drugs, which include Opium and Via contaminated items. Smallpox can also spread
substance formed by its secretion like morphine, through contact with contaminated clothing and
heroin, pethidine, methadonem, etc. bedding, although the risk of infection from these
Effects of intoxicating drugs : See the answer of sources is less common.
Long Questions-2. As a terrorist weapon, potentially. A deliberate release
Q.6. What do you understand by the immune system? Who of smallpox is a remote threat. However, because any
invented the immune system? Write down the release of the virus could spread the disease quickly,
symptoms, transmission and control measures of government officials have taken numerous precautions
smallpox disease. (2017) to protect against this possibility, such as stockpiling
Ans. The ability of an organism to fight against disease smallpox vaccine.
causing agents is called immunity. Several organs of Lesions also develop in the mucous membranes of your
the body participated in the immunity these are nose and mouth and quickly turn into sores that break
collectively called immune system, i.e., lymphoid opne.
organs tissues, cells, etc. Smallpox is a contagious and Prevention : In the event of an outbreak, people who
sometimes fatal disease, caused by a brick-shaped had smallpox would be kept in isolation in an effort to
double-stranded DNA virus of the Poxviridae family. It control the spread of the virus. Anyone who had
is one of the largest virions, approximately the same contact with someone who developed an infection
size of chlamydiae. would need the smallpox vaccine, which can prevent or
An English Physician Edward Jenner invented the lessen the severity of the disease if given within four
immune system. The main parts of the immune system days of exposure to the smallpox virus.
are—WBCs, antibodies, the complement system, the The vaccine uses a live virus that's related to smallpox,
lymphatic system, the spleen, the thymus and the bone and it can occasionally cause serious complications,
marrow. These are the parts of your immune system such as infections affecting the heart or brain. That's
that actively fight infection. why a general vaccination program for everyone isn't
Symptoms : Smallpox pustules covering the trunk of recommended at this time. The potential risks of the
the body Smallpox Open pop-up dialog box. vaccine outweigh the benefits, in the absence of an
The first symptoms of smallpox usually appear 10 to 14 actual smallpox outbreak.
days after you are infected. During the incubation Lab tests suggest certain antiviral drugs may be
period of seven to 17 days, you look and feel healthy effective against the virus that causes smallpox. These
and can't infect others. drugs have not been tested in people who are sick with
Following the incubation period, a sudden onset of smallpox, however, so it's not known if these drugs are
flu-like signs and symptoms occurs. These include: effective treatment options.
Fever, Overall discomfort, Headache, Severe fatigue, Q.7. What do you know about immunity? Name two human
Severe back pain, Vomiting, possibly. vaccines and clarify their importance. (2017)
A few days later, flat, red spots appear first on your Ans. The ability of the body (host) to fight against the
face, hands and forearms, and later on your trunk. disease causing agents is called immunity. It is of two
Within a day or two, many of these lesions turn into types as shown below.
small blisters filled with clear fluid, which then turns (a) Innate immunity: See the answer to Long
into pus. Scabs begin to form eight to nine days later Question-10.
and eventually fall off, leaving deep, pitted scars. (b) Acquired immunity: See the answer to Long
Causes : Smallpox is caused by infection with the Question-10.
variola virus. Principal vaccines used to prevent bacterial/viral
Transmission : Directly from person to person. Direct diseases in human
transmission of the virus requires fairly prolonged
face-to-face contact. The virus can be transmitted
 81

Bacterial Vaccine Recommen- Booster Q.9. Which three main defense methods are used to prevent
Disease dation infection in human body? Describe main features of
Cholera Crude fraction of For people who Every 6 months
immune responses. (2016)
Vibrio cholerae work and live in as needed Ans. Following three main defense methods are used to
endemic areas prevent infection in human body.
(i) First defensive level (Impenetrable level of
Diphtheria Purified For children 2 Every 10 yrs for
diphtheria toxoid months to 16 yrs adults body-skin and mucus layer).
(ii) Second defensive level (Non-specific immune
Meningoco- Purified For people with Need not to be system).
ccal polysaccharide substantial risk of established
from Neisseria infection (iii) Third defensive level (Specific immune system)
meningitidis Main feature of immune response
Immune response induced in animals to produce
Pertussis Killed whole or Children prior to For high-risk
fragments of school age (3-4 adults specific types of protein antibody. For this
(whooping
cough) Bordetella yrs) purpose, lymphocytes present in blood and lymph
pertussis become sensitised towards pathogens entering
inside the body and provide life time protection by
Q.8. Describe specific defence system.
identifying foreign organisms, and destroying
Ans. Animals have immune system to defend from acquired them.
diseases. These immunity feature and associated So, main features of immune response are as
organs are collectively called immune system. White follows:
blood cells participate in this. Main cells of immune
1. Recognition of invader or Detection of foreign
system are T-lymphocytes and B-lymphocytes.
substances: First and main task of immune
Lymphocytes which mature in thymus gland are
responses is to differentiate between own cells or
differentiated into T-lymphocytes and lymphocytes
substances and foreign organisms or substances
which mature in lymph tissues are differentiated in
invading from outside or recognising foreigners
B-lymphocytes.
or invaders. After recognising once, immune
Immune system of two types :
system starts destroying foreign substance.
(i) Cell-mediated immunity: T-lymphocytes
Lymphocytes of immune system perform
become active coming in contact with antigens
recognition and destruction of foreign substances.
and increase in their number by mitotic division
Substances starting immune response starts
which results in the formation of four types of
antigen antibody reactions. Mainly antigens are
lymphocytes.
large molecules of protein. Antibodies attached at
(a) Killer T-lymphocytes: They kill the the surface of T and B-lymphocytes recognize
pathogenic cells by direct attack on them.
antigen. Glycoprotein attached on plasma
(b) Helper T-lymphocytes: Stimulate the activity membrane of foreign cells also functions as
of killer T-lymphocytes and B-lymphocytes. antigens. Our body's lymphocytes recognise these
(c) Suppressor T-lymphocytes: They suppress foreign glycoprotein.
the activity of immune system after the Due to this reason immune system recognises
infection has been finished. cancer cells and tissue graft cells. Some medicines
(d) Memory cells: Some of the cells after coming (Sulfa drug, antibiotics,) toxins, toxoids and some
in contact with pathogens become sensitized chemical substances (Like formaldehyde to
and stored in lymphoid tissue as memory poison), etc. also initiate immune responses.
cells. These cells become instantly active to 2. Overcoming threates or Destruction of
attack by same antigen. antigens: Antibodies destroy foreign organism in
(ii) Antibody-mediated immunity: B-lymphocytes five ways—
produce antibodies; some B-lymphocytes became (a) By neutrilisation: Antibodies make an
active and differentiate into plasma cells. These covering around virus molecules, due to
plasma cells produce antibodies. Some which virus molecules do not stick on the
B-lymphocytes stored in lymphoid tissue as plasma membranes of somatic cells and are
memory cells. When the same attack repeats, incapable of invading them. Similarly
these cells form lacs of similar cells and produce antibodies also gets neutrilised.
antibodies.
 82

(b) Agglutination : Single antibody agglutinates epithelium lining the respiratory, gastrointestinal
many antigens and bacteria by binding with and urogenital tracts also help in trapping
them. Later macrophages destroy these microbes.
antigen-antibody agglutinates by engulfing (ii) Physiological barriers : Tears from the eyes,
them. saliva in the mouth, acid in the stomach, etc.,
(c) Precipitation : Antibodies make antigen prevent the growth of microbes.
insoluble by binding with them. These (iii) Cellular barriers : These include the special types
antigen-antibody complex precipitate and of cells in our body which kill the disease causing
are destroyed by macrophages. agents. These are WBCs like Polymorpho
(d) Opsonisation: Some antibodies cover the Nuclear Leucocytes (PMNL-neutrophils),
surface of bacteria due to which phagocytic monocytes and natural killer cells (type of
cells easily destroys them by eating. lymphocytes) in the blood and macrophages in
Antibodies performing this activity are tissues.
called opsonin. (iv) Cytokine barriers : Cells which are virus-infected
(e) Activation of complementary system : release proteins called interferons that protect
Antigen-Antibody complex activates non-infected cells from further viral infection.
complementary protein molecules of Acquired Immunity
non-specific immune system. The pathogen’s specific immunity. It is not present
3. Memorising invader or Production of memory from birth and develops during an individual’s
cells: Cells of immune system produce memory lifetime. This type of immunity is acquired, either by
cells against invading substances. encountering the disease or by vaccination. It has the
Some memory cells are produced for each antigen following characters :
or pathogen by B and T both lymphocytes, which (a) Specificity : It has the ability to distinguish many
remain in the blood and lymph in dormant state. different foreign molecules.
Such as external antigen invades in the body, all (b) Memory : The ability to memorise the primary
memory cells against that antigen get ready for encounter with a pathogen.
infection by activating themselves, this is called (c) Discrimination : Between self and non-self cells.
secondary immune response. It can be of following two types—
Lymphocyte destroy invaders. Lymphocytes form Active Immunity
in red bone marrow and remain in blood and The immunity developed by the body on exposure to
lymph. These are of two types, i.e., immature and the antigens either in living form or dead microbes or
mature. other proteins. It involves production of antibodies.
Q.10. What do you mean by the term immunological system? Introduction of pathogens or microbes either during
Describe different types of immunological system. immunisation or by any infection induces active
(2017, 18) immunity. It is slow but long lasting and has no side
Ans. Immunological system refers to the association of effects. This immunity may be :
organs and cells involved in defence of a host body. (i) Artificial immunity : developed by vaccination.
The function of this system is to provide immunity (ii) Natural immunity : developed during natural
against disease causing agents like bacteria, fungi, infection.
virus, etc. (b) Passive Immunity
Immunity developed in our body is grouped into The immunity bestowed by antibodies that are directly
following categories. administered in the body. It is fast but lasts only for few
Innate immunity : The defence elements with which days. For example,
an individual is born and which are always available to (i) Antibodies received by foetus from mother
protect the body. It is a non-specific type of defence. It through placenta.
consists of four types of barrier systems that prevent (ii) Antibodies in the colostrum (IgA rich).
the entry of pathogen or foreign element into the body. Colostrum is a yellowish fluid secreted by
There are various types of barriers as given below : mother during the initial days of lactation.
(i) Physical barriers : Skin prevents the entry of the
pathogens into the body. Mucous coating of
 83

NCERT Fully Solved Exercise

Q.1 What are the various public health measures, which (b) Secondary lymphoid organs are spleen, lymph
you would suggest as safeguard against infectious nodes, tonsils, Peyer’s patches of small intestine
diseases ? and appendix.
Ans. Various public health measures, as safeguard against Q.7 The following are some well-known abbreviations,
infectious diseases can be—education of public, which have been used in this chapter. Expand each one
isolation and treatment of the infected ones, to its full form :
vaccination, sanitation, eradication of vectors and (a) MALT (b) CMI (c) AIDS (d) NACO (e) HIV
sterilization. Ans. (a) MALT—Mucosal Associated Lymphoid Tissues.
Q.2 In which way has the study of biology helped us to (b) CMI—Computerized Magnetic Imaging.
control infectious diseases ? (c) AIDS—Acquired Immunodeficiency Syndrome.
Ans. Study of biology has helped us to know about causes of (d) NACO—National AIDS Control Organization.
diseases, carriers of diseases (vectors), effects of (e) HIV—Human Immunodeficiency Virus.
diseases on our body and its functions. Biology has Q.8 Differentiate the following and give examples of each :
also helped us in finding out the control measures of (a) Innate and acquired immunity (2019)
various diseases. (b) Active and passive immunity
Q.3 How does the transmission of each of the following Ans. Please see the answer of Short answer type question-2
diseases take place ? and 1.
(a) Amoebiasis (2020) (b) Malaria Q.9 Draw a well-labelled diagram of an antibody molecule.
(c) Ascariasis (2020) (d) Pneumonia. (2020)
Ans. (a) Amoebiasis : It is caused by Entamoeba Ans. See short answer type Q.No. 3
histolytica. Infection occurs by ingesting cysts Q.10 What are the various routes by which transmission of
with food and drinks. These cysts are carried by human immunodeficiency virus (HIV) takes place ?
flies from faeces to food and drinks. Ans. HIV is transmitted through various routes but it
(b) Malaria : It is caused by Plasmodium sp. Malarial requires the contact of the body fluids of the infected
parasites are carried from the infected to the person and healthy person. Important routes are :
healthy persons by the bite of female Anopheles (i) Unprotected (without condom) sexual intercourse
mosquito. with the infected partner if there is tissue injury to
(c) Ascariasis : Infection occurs by taking Ascaris permit blood contact.
eggs with food and water. Children become (ii) Use of contaminated needles and syringes to
infected by ingesting soiled bed sheets. inject drugs or vaccines.
(d) Pneumonia : It spreads by sputum of the patient. (iii) Use of contaminated razors for shaving.
Infection occurs when Penumococci containing (iv) Transfusion of infected blood or blood products.
droplets are inhaled by a healthy person. (v) Organ transplant, where donor is infected.
Q.4 What measure would you take to prevent water-borne (vi) Parturition from mother to baby due to rupturing
diseases ? of blood vessels.
Ans. Water borne diseases can be prevented by using clean Q.11 What is the mechanism by which the AIDS virus
drinking water and also periodic cleaning and causes deficiency of immune system of the infected
disinfecting of water reservoirs, pools, and tanks. person?
Q.5 Discuss with your teacher what does ‘a suitable gene’ Ans. (i) After getting into the body of the person, the HIV
means, in the context of DNA vaccines. enters macrophages where RNA genome of the
Ans. The term ‘suitable gene’ refers to that gene (specific virus replicates to form viral DNA with the help of
segment of DNA) that will be modified in the host to reverse transcriptase enzyme.
produce specific protein to kill specific disease causing (ii) The viral DNA then gets incorporated into DNA
organisms. of the host cell and directs the synthesis of virus
Q.6 Name the primary and secondary lymphoid organs. particles.
Ans. (a) Primary lymphoid organs are bone marrow and (iii) HIV now enters helper T-lymphocytes, where it
thymus. replicates and produces viral progeny. These
viruses then released into the blood and they
attack other helper T-lymphocytes. In this way,
there is a progressive decrease in number of
 84

helper T-lymphocytes. As a result, person starts Q.15 Do you think that friends can influence one to take
suffering from infections and immune system alcohol/drugs? If yes, how may one protect himself/
becomes weaker. herself from such an influence ?
Q.12 How is a cancerous cell different from a normal cell ? Ans. Yes, friends can influence a person to take alcohol and
Ans. Cancer cell is different from normal cells in following drugs. One can protect himself/herself from such type
aspects : of influences by avoiding experimental use of alcohol
(i) It continues dividing ceaselessly. and drugs for curiosity or pleasure and avoiding the
(ii) It divides in an uncontrolled manner. company of such friends.
(iii) It does not undergo differentiation. Q.16 Why is that once a person starts taking alcohol or
(iv) It forms an ever growing tumour by accumulation. drugs, it is difficult to get rid of this habit? Discuss it
(v) It does not remain confined to a particular place with your teacher.
but shows metastasis. It spread to other places and Ans. Drug and alcohol consumption has an inherent
form secondary tumours. addictive nature associated with euphoria and a
(vi) It invades the neighbouring tissue and dislocate temporary feeling of well-being. Repeated intake of
their functions. drugs increases the tolerance level of the body’s
(vii) Spread throughout the body, forming secondary receptors, leading to more consumption of drugs. So, it
tumours. is very difficult to get rid of this habit.
(viii) It does not show contact inhibition. Q.17 In your view what motivates youngsters to take to
Q.13 Explain what is meant by metastasis ? alcohol or drugs and how can this be avoided ?
Ans. The ability of the cancerous or neoplastic cells to move Ans. Many factors are responsible for motivating
from one place to another place and generate secondary youngsters towards alcohol or drugs. Curiosity, need
tumours is called metastasis. As the tumour cells divide for adventure and excitement, experimentation are the
actively and grow, they even starve the normal cells by initial causes of motivation. Some youngsters start
competing for necessary nutrients. consuming drugs and alcohol in order to overcome
Q.14 List the harmful effects caused by alcohol/drug abuse. negative emotions (such as stress, pressure, depression,
Ans. Alcohol and drug abuse causes severe adverse effects frustration).
on the individual, his family, and the society. Media like movies, television, internet, etc. are also
Effects on individual : When an individual consumes responsible for promoting the idea of taking alcohol to
alcohol/drugs, it causes damage to the liver and the the younger generation. Other reasons such as
nervous system. As a result, other symptoms such as unsupportive family environment and peer pressure
depression, fatigue, aggression, loss of weight and can also push these individuals towards drugs.
appetite are observed. The spread of HIV is most Preventive measures against addiction of alcohol and
common in such individuals as they share common drugs:
needles for injecting drugs in their body. A person (a) Parents should educate their children about the
dependent on drugs becomes frustrated, irritated, and ill-effects of alcohol.
anti-social. (b) Parents should motivate and try to increase the
Effects on the family : Consumption of excess alcohol will power of their child.
by any family member can have devastating effects on (c) Parents should watch their children carefully for
the family. It leads to several domestic problems such their activities.
as quarrels, frustrations, insecurity, etc. (d) Children should be encouraged to devote their
Effects on the society : energy in other extra-curricular and recreational
(a) Rash behavior. activities.
(b) Malicious mischief and violence. (e) Proper professional and medical help should be
(c) Deteriorating social network. provided to a child if sudden symptoms of
(d) Loss of interest in social and other activities. depression and frustration are observed.

ccc

Note : Due to Covid-19 Chapter-9 (Strategy for Enhancement in Food Production) is

not in the Latest Syllabus 2020-21.
Chapter 9 : Strategy for Enhancement in Food Production
(This Chapter has been Deleted From Syllabus For Session 85

2020-21 Due To COVID-19 Epidemic)

Chapter

10
MICROBES IN
HUMAN WELFARE

² Saprophytes are the micro-organisms, which obtain their food from dead and decaying organic matter.
² Lactic acid bacteria are rod shaped bacteria.
² In our stomach, LAB also helps us by checking the growth of other micro-organisms.
² Fermentation is a process of chemical change caused by organisms or their products, usually producing effervescence and heat.
² Fermentation involves anaerobic oxidation.
² Mycorrhiza is the symbiotic associationship of fungi with the roots of higer plants.
² The first antibiotic was discovered accidentally by Sir Alexander Fleming, while working on Staphylococci bacteria. This antibiotic
was Penicillin as it was isolated from a fungus, Penicillium notatum.
² Streptokinase, produced by Streptococcus and modified by gene engineering is used as a ‘clot buster’ i.e., it helps in removing clots from
the blood vessels in persons, who have undergone myocardial infarction.
² Secondary treatment of sewage water is also called biological treatment.
² Anaerobic sludge digesters can produce biogas.
² The technology of biogas production in India was developed mainly due to the efforts of IARI (Indian Agricultural Research Institute)
and KVIC (Khadi and Village Industries Commission).
² In 1961, a Gobar Gas Research Station was also established at Ajitmal (district Etawah in U.P.), which has designed a variety of ‘gas
plants’ suited to Indian conditions and supplying electricity at a cheap rate.
² Bacillus thuringiensis is a bacterium that produces toxins, which are harmful for insect larvae.
² Bt Cotton is a genetically engineered plant, containg toxin producing gene of bacterium, Bacillus thuringiensis.
² Azospirillum and Azotobacter are free living nitrogen fixing bacteria.
² Some fungi such as Glomus also form symbiotic associations with plants (mycorrhiza).

Multiple Choice Questions 1 Mark

Q.1. Biogas is produced by: (c) Bacillus megathermus and Xanthomonas sp.
(a) Bacteria (b) Archaebacteria (d) Lactobacillus and Streptococcus
(c) Mycoplasma (d) Cyanobacteria Q.5. Baker’s yeast is :
Q. 2. The free living fungus Trichoderma can be used for: (a) S. cerevisae (b) S. ludwingii
(a) Killing insects (c) S. octosporous (d) Schizosaccharomyces
(b) Biological control of disease Q. 6. First discovered antibiotic is :
(c) Controlling caterpillars (a) Penicillin (b) Azithromycin
(d) Producing antibodies (c) Amphoterecin (d) Chloromycal
Q.3. Which one of the following is not a nitrogen fixing Q.7. Bacillus thuringiensis is used as :
organism? (a) Biofertilizer (b) Biopesticide
(a) Anabaena (b) Nostoc (c) Bioenergy source (d) All of these
(c) Azotobacter (d) Pseudomonas Q.8. In september 2001, which of the following was used as
Q.4. Which group is responsible for formation and flavour a bioweapon agent in America?
of yoghurt? (a) Anthrax (Bacillus anthracis)
(a) Bacillus subtilis and E.coli (b) Botulinum
(b) Rhizobium meliloti and Azotobacter (c) AIDS virus (d) Polio virus
 86

Q.9. Nitrate found in soil is converted into nitrogen by: (c) Pseudomonas (d) All of these
(2018) Q.12. Bacillus thuringiensis is a :
(a) Rhizobium (b) Azotobacter (a) Mould (b) Bacteria
(c) Pseudomonas (d) All of these (c) Virus (d) Algae
Q.10. Which fungus is used in production of alcohol from Q.13. Antibiotics obtained mainly from : (2020)
sugar? (2018) (a) Blue-green algae (b) Bacteria
(a) Yeast (b) Penicillium (c) Bryophyta (d) Virus
(c) Rhizopus (d) Mucour Q.14. Who discovered penicillin? (2020)
Q.11. Which of the following has symbiotic relation with (a) Herbert Boyer (b) Swaminathan
root nodules found in leguminous plants? (2018) (c) Ram dev Mishra (d) A. Fleming
(a) Rhizobium (b) Azotobacter

Answers
1. (b) 2. (a) 3. (d) 4. (d) 5. (a) 6. (a) 7. (b) 8. (d) 9. (c) 10. (a)

11. (a) 12. (b) 13. (b) 14. (d)

Very Short Answer Type Questions 1 Mark

Q. 1. Define pasteurization? Ans. Azolla pinnata, Anabaena and Nostoc are used as
Ans. It is a method of preserving milk by killing all the bio-fertilizers.
pathogens present in it. This is achieved by heating the Q.12. Write down the names of components of biogas. (2018)
milk sample at a particular temperature for specific Ans. Methane (CH 4 ), CO 2 and hydrogen are the
time period. components of biogas.
Q. 2. Name two free-living nitrogen fixing microbes. Q.13. What is the contribution of yeast cell in the formation
Ans. Azotobacter and Clostridium. of dough? (2014)
Q. 3. What is biogas? (2018) Ans. Yeast on fermentation breaksdown the sugar, CO 2 and
Ans. Biogas is a mixture of methane, carbon dioxide,
C 2 H 5 OH are formed. It has a major contribution in the
hydrogen sulphide and ammonia.
formation of dough which can be used to make food
Q. 4. Give the name of bacteria which converts the lactose products.
sugar of milk into lactic acid?
Q.14. Which bacteria is used in the production of vinegar?
Ans. (i) Streptococcus lactis
(2018)
(ii) Lactobacillus lactis
Ans. Acetobacter aceti
Q.5. Who discovered the Penicillin? (2011)
Q.15. What is the importance of Rhizobium in agriculture?
Ans. Alexander Fleming discovered the penicillin from a
(2018)
fungus named Penicillium notatum.
Ans. It fixes the nitrogen in soil.
Q.6. Give the name of any two antibiotics?
Q.16. Which micro-organism is used for fermentation of tea
Ans. (i) Streptomycin— obtained from Streptomyces
leaves? (2018)
griseus
Ans. Micrococcus candidans
(ii) Chloromycetin— obtained from S. venezuelae.
Q.17. What is leguminous haemoglobin? (2018)
Q. 7. What are bio-fertilizers? (2016)
Ans. Leguminous haemoglobin or leghaemoglobin is an
Ans. Bio-fertilizers are organism that enrich the nutrients in
oxygen carrier haemoprotein, which is found in the
the soil.
nitrogen fixer root nodules of leguminous plants. It
Q.8. Give an example of rod shaped bacteria?
supplies O 2 to cells of symbiotic bacteria for
Ans. Tobacco mosaic virus.
respiration.
Q.9. What is sewage?
Q.18. Discuss the role of blue-green algae (cyanobacteria) in
Ans. The untreated or semi-treated household, waste water,
increasing the fertility of the soil in brief. (2019)
containing human and animal excreta and fecal matter
Ans. Blue-green algae (BGA) are photosynthetic nitrogen
is called sewage.
fixers and are free living. Increase in soil phosphate by
Q.10. When was Ganga Action plan started?
excretion of organic acid. Increasing rice growth and
Ans. ‘Ganga Action Plan’ was started in 1985.
yield as a natural biofertilizer.
Q.11. Write any two microbes used as bio-fertilizers.
 87

Short Answer Type Questions 2 & 3 Marks

Q.1. How microbes help in the making of drinks and bread? enzyme and many acids. These products are very
(2011) useful for mankind. Its importance and clear from
Ans. Microbes are helpful in the production of drinks following points.
generally alcoholic drinks. 1. Some bacteria like Bacillus megatherium and
Alcohol is made by fermenting different food products Micrococcus candidans are used in tobacco
with the help of yeast. Along with it CO2 and alcohol industry.
are also formed. Alcohol is separated through 2. Micrococcus candidans is also used in curing of
distillation. Alcoholic drinks consists of beer, rum, tea leaves, which causes the special taste of tea.
whisky, wine etc. 3. Antibiotic medicines are prepared by the some
Zymase bacteria like.
C 6 H12 O 6 ¾¾¾®
Yeast
2C 2 H 5 OH + 2CO 2 + Heat (i) Bacillus brevis — Thyrothrin
(ii) Streptomyces primosus — Terramycin
Microbes are also used in the making of bread dough.
(iii) S. fradiae — Neomycin
Yeast is put for fermentation. During respiration it
4. Vinegar is obtained by the action of bacterium
gives CO2 gas which results in pores in dough.
Acetobacter aceti with sugar solution.
Generally in bakery products Saccharomyces yeast is 5. Some vitamins like vit. B2 and vit. C is obtained
used. from bacterium Clostridium acetobutylicum and
Q.2. What is meant by BOD? Acetobacter respectively.
Ans. This is the amount of oxygen present in water for the Q.5. Write the constituent gases of biogas and write its two
degradation of organic and other human pollutants by benefits for human beings? (2016, 17, 18)
microbes. Biological oxygen demand gives the Or What is biogas? Give two uses of biogas in rural
measure of oxygen required by microbes to areas. (2017)
degradation of pollutants in 1 litre of water. More BOD
Ans. Biogas or gobar gas is a methane rich gas. This gas is
is an indication of more polluted water.
produced by the fermentation or degradation of
Q.3. Explain the advantage and disadvantages of Biogas? biomass. The energy released from biogas depends
Ans. Advantages: upon the proportion of methane present in it.
1. Biogas provides a non-polluting and renewable
Constituents of biogas :
source of energy.
2. Efficient way of energy conversion. Name of gas Chemical formula Percentage
3. Leads to improvement in the environment, and Methane CH4 50-68%
sanitation and hygiene. Carbon dioxide CO2 25-35%
4. Leads to employment generation in the rural Hydrogen H2 1-15%
areas. Nitrogen N2 2-7%
5. Any biodegradable matter can be used as
Oxygen O2 0.01%
substrate.
6. Household wastes and bio-wastes can be disposed Hydrogen sulphide H2 S Very small amount
off usefully and in a healthy manner. Benefits :
Disadvantages: (i) It provides fertilisers in farms.
1. This process is not very attractive, economically (ii) This gas is used in producing electricity and for
or a large industrial scale. cooking.
2. It is very difficult to enhance the efficiency of Q.6. What do you understand by biofertilizers? Write the
biogas systems. name of any two nitrogen fixing bacteria. (2017, 20)
3. Biogas contains some gases as impurities, which Or What are biofertilisers? Why is it used more than
are corrosive to the metal parts of internal chemical fertilisers? (2016)
combution engines. Or Micro-organisms used as bio-fertilizers.
4. Not feasible to locate at all the locations. “Microbes can be used to decrease the use of chemical
Q. 4. Give the importance of bacteria in industrial products. fertilizers and pesticides”. Justify the statement. (2019)
Or Describe the importance of micro-organisms in Or What do you understand by biofertilisers? Give its
industrial production with examples. (2019) source and usefulness. (2019)
Ans. Bacteria or microbes gives their contribution in making Or Write a short note on biofertilizers. (2020)
wine, vinegar, antibiotics and chemicals such as
 88

Ans. Biofertilisers are the microbial organism that have the Formation of cheese, also involves the use of microbes.
ability to enrich the nutrient quality of the soil. The The flavour and taste of different varieties of cheese is
main sources of biofertilisers are bacteria, fungi and due to use of specific microbes. For example, the
cyanobacteria. bacterium, Propionibacterium sharmanii produces
Some of the microbes (nitrogen-fixing) produce large holes in ‘Swiss cheese’ due to the production of a
nitrogen in the environment by fixing nitrogen, e. g., large amount of CO 2 . The ‘Roquefort cheese’ which
Rhizobium, Acetobacter, Azolla, etc. They are nitrogen is a blue cheese prepared from sheep’s milk, is ripened
fixing organisms. by growing a specific fungus (Penicillium roqueforti)
Micro-organisms protect the plants from the bad on it.
effects of other insects. Some organisms also take part Q.8. Explain the use of micro-organism in the production of
in the production of humun in soil. energy (Biogas)? (2018)
Many members of the genus Glomus (fungi) form Or What is the role of micro-organisms in production
symbiotic associations with plant known as of biogas. (2019)
mycorrhiza that Or Write a short not on the role of microbes in biogas
â absorb phosphorus from soil and pass it to the plant. production. (2020)
â help the plants to develop resistance to root-borne Ans. Microbes like methanogens and Methanobacter are
pathogens. used for the production of ‘biogas’ which is used as
â increase their tolerance to salinity and drought and energy source. The major part of biogas, consists of
thus, help in overall increase in plant growth and methane (50-70%). Other constituents of biogas are
development. CO 2 (30-40%), small amount of hydrogen, nitrogen
Biofertilisers are preferred over because chemical ethylene, acetylene, ethane, propane and a very little
fertilisers. amount of hydrogen sulphide (H 2 S).
(i) Chemical fertilisers are expensive as well as The excreta of cattle, i. e., cattle dung (commonly
harmful for the soil. They decrease the fertility of known as gobar) is rich in methanogenic bacteria, is
the soil and make it infertile. used in the generation of biogas or gobar gas.
(ii) Their excess usage creates a bad effect on human Biogas plant optimises the utilisation of manure, waste
body. and these organic feed stock by converting the
(iii) Usage of coal and petroleum in production biomasses into energy and valuable bio-fertilisers.
increases pollution. Biofertilisers keep the Biogas was developed in India by Khadi and Village
structure of soil intact as well as the fertility of soil Industries Commission (KVIC) and Indian
is also not damaged. Agricultural Research Institute (IARI).
Q.7. What is fermentation? Give it economic importance. Q.9. Explain the medicinal uses of micro-organisms.
(2018) (2018)
Ans. Fermentation is a process of chemical change caused Or Write the name of any three fungal spceies which
by organisms or their products, usually producing are used in the production of antibiotic. (2019)
effervescence and heat. Microbiologists consider Ans. 1. Use of bacteria in production of antibiotic :
fermentation as ‘any process for the production of a Antibiotics Bacteria
product by means of mass culture of micro-organisms’. 1. Streptomycin Streptomyces griseus
The product formed as a result of fermentation are 2. Aureomycin S. aureofaciens
called fermented food. 3. Terramycin S. rimosus
Fermentation is used in the production of many 4. Chloromycetin S. venezuelae
products, such as bear (and also other alcoholic 2. Use of fungus in production of antibiotic :
beverages), bread, yogurt, cheese, idly, dosa etc. The Antibiotic Fungus
dough, used in dosa and idli is also a fermented 1. Penicillin Penicillium notatum
product. The puffed-up appearance of dough is due to 2. Ergot Claviceps purpurea
the production of CO 2 gas. The dough, which is used 3. Clavicin Aspergillus claveus
for making bread, is also fermented by using baker’s 4. Cephalosporin Cephalosporium
yeast (Saccharomyces cerevisiae). acremonium
Many traditional drinks are also made by fermentation 3. Use of fungus in production of enzyme :
by the microbes. For example, ‘Toddy’, which is Enzyme Fungus
traditional in southern India is made by fermenting sap 1. Invertase Yeast, Alternaria
from palms. 2. Amylase Aspergillus oryzae
3. Renate protease Mucor
 89

4. Use of bacteria in synthesis of various medicinal process in which certain types of bacteria convert the
substances : biological wastes into useful biogas. Since the useful
Product Bacteria gas originates from biological process, it has been
1. Dextron Leuconostoc termed as biogas. Methane gas is the main constituent
2. Vitamin B2 Clostridium acetobutylicum of biogas.
3. Vitamin B12 Streptomyces oliasis Components of biogas plants:
4. Vitamin C Acetobacter (i) Mixing tank : The feed material (dung) is
Q.10. Write the importance of microbes in household collected in the mixing tank. Sufficient water is
products. (2018) added and the material is thoroughly mixed till a
Or Describe the role of micro-organisms in production homogeneous slurry is formed.
of domestic food material. (2019) (ii) Inlet pipe : The substrate is discharged into the
Ans. Microbes in household products : Microbes are used digester through the inlet pipe/tank.
in household products in day-to-day life, e. g., curd is (iii) Digester : The slurry is fermented inside the
digester and biogas is produced through bacterial
made by Lactobacillus, commonly called Lactic Acid
action.
Bacteria (LAB). It grows in milk and converts it into
(iv) Gas holder or gas storage dome : The biogas gets
curd, during growth. The amount of curd added as raw
collected in the gas holder, which holds the gas
material to convert milk into curd is known as
until the time of consumption.
inoculum. The dough which is used for making foods
(v) Outlet pipe: The digested slurry is discharged into
as dosa, idli, cakes and bread are also fermented by
the outlet tank either through the outlet pipe or the
bacteria or yeast (Saccharomyces cerevisiae).
opening provided in the digester.
Toddy is a traditional drink of Southern India. It is (vi) Gas pipeline: The gas pipeline carries the gas to
made by fermenting sap from palm trees, coconut, etc. the point of utilization, such as a stove or lamp.
Cheese is also made by using microbes. Different
Gas
varieties of cheese are known by taxture, flavour and Dung Water
Mixing pipeline
Gas
taste. These specifity comes from propionibacterium tank
holder Sludge
shermanii in Swiss cheese and Penicillium roqueforti
Outlet
in roquefort cheese. pipe
Q.11. What do you understand by antibiotic? Write down the
names of any two antibiotics. (2019) Inlet pipe
Ans. Antibiotic is a medicine which is used for destroying
bacteria and curing infections. Digester tank
Streptomycin and Chloromycetin are two antibiotics.
Q.12. Name any two species of fungus and the antibiotics Fig. A typical biogas plant
produced by them. (2019) Q.15. How chemical fertilizers are differen from
Ans. Please see the ans. of Short answer type question-9. bio-fertilizers? (2020)
Q.13. What is the key defference between primary and Ans. Difference between chemical fertilizers and bio-
secondary sewage treatment? (2019) fertilizers
Ans. Key differences between primary and secondary
Chemical fertilizers Bio-fertilizers
sewage treatment are as follows :
(i) These are manufactured These are manufactured
Primary Secondary artificially. naturally.
Sewage treatment Sewage treatment
(ii) These are primarily, These are plants such as
It is a physical process. It is a biological process. chemicals having N, bacteria (Azotobacter,
It involves physical It involves the action of phosphate and K as main Rhizobium), fungi etc.
removal of solid material. microbes. soil nutrients.
It is less complicated and It is a complicated and an (iii) These deteriorates to soil These improve to soil
not expensive. expensive process. health. health.
(iv) These have high cost. These have low cost.
Q.14. What is biogas? Describe a typical biogas plant with
(v) These are non-renewable. These are renewable.
the help of a diagram. (2019)
Ans. Biogas : It mainly comprises of hydrocarbon which is Q.16. Explain the significance of micro-organisms in sewage
combustible and can produce heat and energy when treatment. (2020)
burnt. Biogas is produced through a bio-chemical
 90

Ans. Anaerobic bacteria are used in waste water treatment If bacteria can infect a host, multiply inside the body
on a normal basis. The main role of these bacteria is and eventually spread to another organism, it exhibits
sewage treatment is to reduce the volume of sludge and the behavior of a parasite. Many bacterial diseases do
produce methane gas from it. The great thing about this this. In particular, food-borne illness such as
type of bacteria and why it is used more frequently than Salmonella exhibit this behavior. Other examples of
aerobic bacteria is that the methane gas, if cleaned and bacteria that act as parasites are those which cause
handled properly, can be use as an alternative energy sexually transmitted diseases. The bacteria that causes
source. syphilis and gonorrhea use the natural function of
Unlike aerobic bacteria, this type of bacteria is able to human hosts to multiply and spread. Additional
get more than enough oxygen from its food source and bacteria that act as parasites include those that cause
will not require adding oxygen to help do its job. the diseases cholera, small pox and the Bubonic
Phosphorus removal from waste water is another plague.
benefit of anaerobic microbes used in sewage Q.18. Define the antibiotic. Who discover the penicillin?
treatment. Explain the significance of penicillin. (2020)
Q.17. What are parasite bacteria? Describe it by giving an Ans. Antibiotic are chemical substances, which are
example. (2020) produced by some microbes and can kill or retard the
Ans. While some bacteria are parasites, not all bacteria are. growth of other microbes.
Neither are all parasites bacteria. Parasites can be any Penicillin was discovered by Alexander Fleming.
organism that uses another as a host, and sometimes Penicillin prevents the bacteria from synthesizing
that parasitic organism is bacteria. It depends on the peptidoglycan, a molecule in the cell wall that provides
life cycle of the parasitic organism and how it uses the the wall with the strength it need to survive in the
host. The bacteria that causes strep throat acts as a human body. The drug greatly weakens the cell wall
parasite in the human body because it uses the host to and causes bacteria to die, allowing a person to recover
multiply and eventually spread to another organism. from a bacterial infection.

Long Answer Type Questions 5 Marks

Q.1. Write comments on the followings. (iii) Dextran is another polysaccharide of microbial
(a) River Action Plan origin produced by Leuconostoc mesentero.
(b) Microbes in Sewage Treatment Dextran is used to extend blood plasma.
(c) Bioactive Molecules (iv) Nutrients like amino acids, nucleotides, vitamins
(d) Mycorrhizal Association are also produced by micro-organisms. e. g., The
Ans. (a) River Action Plan : In order to protect the major lysine is a product of the bacterium
rivers of India from sewage pollution. The Corynebacterium glutamicum. Vitamin B12 and
ministry of environment and forests of India has vitamin B2 are produced by a bacterium and a
initiated Ganga Action Plan and Yamuna Action mold respectively.
Plan under the National River Authority. Under (d) Mycorrhizal association : Fungi are known to
these plans, it is proposed to build a large number form symbiotic associations with plants. Many
of sewage treatment plants so that only treated members of the genus Glomus form mycorrhiza.
sewage may be discharged in the rivers. Uttar The fungal symbiont in these associations absorbs
Pradesh Government 2011 set up the Asia's phosphorus from soil and passes it to the plant.
largest sewage treatment plant at Lucknow. Plants having such associations show other
(b) Microbes in Sewage Treatment: Refer Q. No. 2 benefits also, such as resistance to root-borne
(L.A.). pathogens, tolerance to salinity and drought and
(c) Bioactive Molecule : an overall increase in plant growth and
(i) Cyclosporine–A is a bioactive molecule that is development.
used as an immunosuppressant agent in Q.2. Describe the sewage treatment giving its all steps
organ-transplant patients. It is produces by the showing flow chart.
Trichoderma polysporum. Ans. Pollution due to sewage, animal waste and effluents
(ii) Statin is a chemical agent produced commercially from industries is a big problem. Micro-organisms can
by the yeast Monascus purpureus. It is used for be very helpful in converting the harmful sewage and
lowering the blood cholesterol level. effluent water into harmless water. They can also
 91

convert the sludge (organic waste) into inorganic The processes occurring in aeration tank, kill
compounds. infectious bacteria leaving non-pathogenic bacteria
A sewage treatment plant is nothing more than a giant and harmless organic matter.
microbial culture breeding facility. They effectively When the BOD is reduced significantly, the water is
use up unwanted nutrients in the system, by transferred to a settling tank, where bacterial flocs are
metabolizing the solid waste that passes through the allowed to settle down (sediment). This sediment is
treatment plant. The microbes oxidize the organic called activated sludge. (a small part of activated
waste and produce inorganic chemicals like sludge may be used in the aeration tank as inoculum).
phosphates, nitrates and sulphates. The process is The major portion of activated sludge can be pumped
called mineralization. Gaseous by-products to large tanks for ‘anaerobic sludge digesters’.
carbon-dioxide are also produced. Both aerobic and During this digestion, anaerobic bacteria produce
anaerobic microbes are used in the treatment process. gases like methane, CO 2 and H 2 S etc., which together
In the first instance, aerobic microbes breakdown the form biogas.
large organic compounds. These are supplied with Reduction
Growth of in BOD level Settling
excess oxygen to promote vigorous reactions. microbe masses Effluent
tank
In essence, sewage treatment has two functions : (flocs)
o To kill pathogens (whatever they are) and

Constant
agitation
o To eliminate harmful chemicals from the water.
Flocs
o Chemicals that are toxic and the bulk of organic

Released into natural water bodies

sediment
chemicals that cause the depletion of
life-supporting oxygen in the receiving waters of a
stream, river or lake. Air Sma
Working of Sewage Treatment Plant : Large as in ll part
oculu
aeration m Activated
It involves three types of treatments—1. Primary, Sludge
2. Secondary and 3. Tertiary treatment. tank
1. Primary Treatment : It includes physical processes
like separation of large debris, gravels, insects, and
sedimentation etc. using appropritate filters. Primary Effluent Anaerobic
treatment involves different steps. In the first stage, sludge
Sedimentation

digester
floating debris are removed by sequential filtration. (large tank)
After this, the girt (soil and small pebbles) are removed Grit (soil and

Digestion
by sedimentation. All solids that settle down, form the small pebbles)
primary sludge and the supernatant forms the effluents. Primary
The effluent from the primary settling tank is taken for sludge
Sequential

secondary treatment. (i.e., primary sludge is removed

filtration

Biogas
off). Floating
2. Secondary Treatment : It is also called biological debris
treatment as it involves the use of micro-organisms
in oxidation ponds or activated sludge process. The Sewage
effluents from the primary treatment are passed into waste
large aeration (oxidation) tank, which is a shallow Fig. Flow chart showing sewage treatment strategy
water reservoir. The water in the tank is constantly
The supernatant (clear water), may be subjected to
agitated mechanically and air is pumped into it. This
tertiary treatment (or may be released to natural water
procedure allows sufficient aeration of the water and
bodies).
promotes the vigorous growth of micro-organisms in it.
3. Tertiary Treatment : It involves physico-chemical
The masses of bacteria associated with fungal processes that remove turbidity in the waste water (due
filaments are formed. These are called flocs. These to nitrogen and phosphorus etc.). This treatment
form mesh like structures. These biological agents involves the oxidation of waste-water by strong
consume most of the organic matter present in the oxidising agents (like chlorine, per chlorate salts,
primary effluent. This reduces the BOD (biological ozone gas and UV radiations). After tertiary treatment,
oxygen demand) of the water. the water can be discharged into natural water and can
be used for irrigation purpose.
 92

NCERT Fully Solved Exercise

Q.1 Bacteria cannot be seen with the naked eyes, but these (b) Penicillium griseofulvin — Griseofulvin
can be seen with the help of a microscope. If you have Q.7 What is sewage? In which way can sewage be harmful
to carry a sample from your home to your biology to us ? (2020)
laboratory to demonstrate the presence of microbes Ans. The untreated or semi-treated household waste water,
under a microscope, which sample would you carry containing human and animal excreta and fecal matter
and why ? is called sewage. It is harmful because it contains many
Ans. For demonstration, we would carry a small sample of harmful bacteria and promotes the growth of
curd. This is because the curd is easily available and it pathogens.
contains large number of Lactobacillus bacteria. Q.8 What is the key difference between primary and
Q.2 Give examples to prove that microbes release gases secondary sewage treatment? (2020)
during metabolism. Ans. Please see the answer of Short answer type
Ans. Bacteria and fungi (Yeast) carry out the anaerobic question-13.
process of fermentation. During this process, they Q.9 Do you think microbes can also be used as source of
release carbon dioxide. Two examples are given energy? If yes, how ?
below: Ans. See the answer of Short answer type question-8.
(a) Fermentation of sugars produces alcohol with the Q.10 Three water samples namely river water, untreated
release of carbon dioxide. sewage water and secondary effluent discharged from
(b) The dough used for making idli and dosa gives a a sewage treatment plant were subjected to BOD test.
puffed appearance due to the releases carbon The samples were labelled A, B and C; but the
dioxide. laboratory attendant did not note which was which.
Q.3 In which food would you find lactic acid bacteria? The BOD values of the three samples A, B and C were
Mention some of their useful applications. recorded as 20 mg/L, 8 mg/L and 400 mg/L,
Ans. Lactic acid bacteria (LAB) are present in curd. Its respectively. Which sample of the water is most
useful applications are : polluted? Can you assign the correct label to each
(a) It converts milk into curd which is used for assuming the river water is relatively clean ?
making many food articles. Ans. Sample C with BOD value 400 mg/L is the most
(b) Lactobacillus checks the growth of many harmful polluted. This is because, the BOD values are high
bacteria in the stomach. when amount of oxygen dissolved in water is very less.
Q.4 Name some traditional Indian foods made of wheat, So, this represents the poor oxidation state of the
rice and Bengal gram (or their products) which involve organic matter present in the sample. Hence it is the
use of microbes. most polluted one.
Ans. (a) Wheat products, which involve the use of Q.11 Find out the name of the microbes from which
microbes : Bread, cake, etc. Cyclosporin A (an immunosuppressive drug) and
(b) Rice products, which involve the use of microbes: Statins (blood cholesterol lowering agents) are
Idli, dosa. obtained.
(c) Bengal gram products, which involve the use of Ans. Cyclosporin A — Trichoderma polysporum
microbes : Dhokla, Khandvi. Statins — Monascus purpureus
Q.5 In which way have microbes played a major role in Q.12 Find out the role of microbes in the following.
controlling diseases caused by harmful bacteria ? (a) Single cell protein (SCP)
Ans. Micro-organisms are used to obtain certain drugs (b) Soil
called antibiotics. These drugs are very effective Ans. (a) Single Cell Protein (SCP) : A protein extracted
against a wide variety of pathogens. In this way, from cultured algae, yeasts, or bacteria and used
microbes have played a major role in controlling as a substitute for protein-rich foods, especially in
diseases caused by harmful bacteria. animal feeds, is known as single cell protein
Q.6 Name any two species of fungus, which are used in the (SCP).
production of the antibiotics. Bacteria, yeast and unicellular algae are all single
Ans. The two species are : celled organisms. They can be cultured rapidly on
(a) Penicillium notatum — Penicillin simple culture medium and can be forced to
 93

produce various proteins of importance. Q.13 How do biofertilisers enrich the fertility of the soil ?
Commercial production of SCP is mostly based (2020)
on the use of yeast and some other fungi, such as Ans. Biofertilisers mainly help in enriching the soil with
Fusarium graminearum etc. appropriate nitrogenous contents. Although 78%
(b) Soil : Soil contains many micro-organisms nitrogen is present in air, none of the plant cannot take
including many bacteria and fungi. These it directly from aerial parts. So, nitrogen can be taken in
microbes convert the dead and decaying matter in to the plant body only in organic form. Biofertilisers
to humus which make the soil fertile. contain organisms like cyanobacteria, Azotobacter
Furthermore, bacteria like Azospirillum and etc., which can fix atmospheric nitrogen into
Azotobacter fix the atmospheric nitrogen and biologically useful form.
enrich the fertility of the soil.

ccc
 94

Chapter

11
Unit-4 : Biotechnology
BIOTECHNOLOGY :
PRINCIPLES
AND PROCESSES

² Study of genome is called genomics.

² Restriction endonuclease enzymes are also called molecular scissors.
² Monozygotic twins are clones.
² Retro-viruses can carry out reverse transcription.
² Genetic material in all retro-viruses is RNA.
² Term ‘cloning’ is applied to living structures only.
² First cloned mammal was a sheep, named Dolly.
² Meristematic cells of plants are totipotent in nature.
² Totipotency of animal cells is lost due to a high degree of specialisation and differentiation.
² Transgenic crops give rise to genetically modified food (GMF).
² Production of a large number of plantlets in culture medium is called micro-propagation.
² Only totipotent cells can produce their clones naturally.
² Offspring produced as a result of asexual reproduction, are natural clones.
² Two clones must have a similar genetic configuration.
² Direct gene transfer does not involve any vector. This can be achieved by gene guns.
² Artificial chromosomes, obtained from bacteria are called BACs and those, obtained from a yeast cell are called YACs.
² BACs and YACs can be used as a vector during genetic engineering.
² Ti plasmid is present in Agrobacterium tumefaciens.
² Agrobacterium tumefaciens infects many vegetable crops and causes cancerous growth, called Crown Gall Tumour.
² A specific portion of Ti plasmid is called T-DNA.
² SCID stands for Severe Combined Immuno Deficiency.
² SCID is genetic disorder, in which the gene, producing adenosine deaminase (ADA) becomes defective.
² Hybridoma cells are produced by fusing a lymphocyte with a cancerous cell (myeloma).
² Transgenic organisms are called genetically modified organisms (GMOs).
² Bacillus thuringiensis produces ‘Cry proteins’ which are insecticidal in nature.
² Flavr savr is a transgenic tomato.
² Bt-cotton is transgenic cotton, produced by inserting, cry protein-forming gene of Bacillus thuringiensis bacterium, into a normal cotton
plant. This variety is resistant to insect and larval attack.
² The technique of DNA fingerprinting was developed by Alec Jeffreys.
² The DNA of all persons carries small tandemly repeated sequences of nucleotides. These are called VNTRs.
² VNTRs stand for ‘Variable Number Tandem Repeats’.
² Probe is a radioactive strand of DNA often used to find particular sequences in a ‘Southern Blot’ during DNA finger printing.
² The first recombinant DNA was made by Stanley Cohen and Herbert Boyer (1972), using the plasmid of Salmonella typhimurium.

Multiple Choice Questions 1 Mark

Q.1. Who discovered restriction enzyme? (c) Arber smith and Nathan
(a) Fleming (d) Burgar
(b) Waksman
 95

Q.2. Which enzyme is used to obtain specific DNA (a) RNA (b) Ribonucleoprotein
fragment? (c) Simple protein (d) Recombinant DNA
(a) Ligase Q.8. Plasmids are found in which cells of the following?
(b) Lipase (a) Animal cells (b) Plant cells
(c) Hydrolase (c) Bacterial cells (d) Diseased infected cells
(d) Restriction endonuclease Q.9. Identifies of DNA fragments by : (2017)
Q.3. Which obtain from genetic engineering? (2017) (a) Northern blotting (b) Southern blotting
(a) Glucose (b) Wheat (c) Western blotting (d) All of these
(c) Maize (d) Golden rice Q.10. Proper vectors of cloning in animal cells is : (2018)
Q.4. Transformed antibiotics are formed by which (a) SV 40 (b) pBR 327
technique? (c) pUC (d) pBR 322
(a) Genetic engineering (b) Rapid centrifugation Q.11. Restriction endonucleases are used in genetic
(c) Convergence (d) Microfiltration engineering to form : (2019)
Q.5. Which of the following is use as a best genetic vector in (a) Recombinant DNA molecule
plants? (b) Recombinant RNA molecule
(a) Agrobacterium tumefaciens (c) Recombinant molecule of both DNA and RNA
(b) Psuedomonas putida (d) None of these
(c) Bacillus thuringiensis Q.12. Which enzyme joins the DNA segments? (2019)
(d) None of the above (a) Ligase (b) Endonuclease
Q.6. Plasmids is : (c) Exonuclease (d) Chitinase
(a) Double stranded circular DNA Q.13. Which of the following enzyme cut the DNA at
(b) Single stranded DNA specific site? (2020)
(c) Extrasomal linear DNA (a) Exonuclease (b) Endonuclease
(d) None of the above (c) Polymerase (d) All of these
Q.7. Telomerase enzyme is :

Answers
1. (c) 2. (d) 3. (d) 4. (a) 5. (a) 6. (a) 7. (b) 8. (c) 9. (b) 10. (a)

11. (a) 12. (a) 13. (b)

Very Short Answer Type Questions 1 Mark

Q.1. What do you understand by biotechnology? (2012, 13) Ans. The source is the bacterium Thermus aquaticus. It is
Ans. Biotechnology is an integrated branch of biology used because it is thermostable and do not denature at
which deals with the technologies of using live high temperatures.
organism or enzymes from organisms in order to Q.5. How does an alien DNA gain entry into a plant cell by
produce different products and processes useful to ‘biolistics’ method ?
humans. Ans. In biolistics, the cells are bombarded with high velocity
Q.2. What is EcoRI ? How does EcoRI differ from an micro-particles of gold or tungsten coated with DNA.
exonuclease ? Q.6. What are cry proteins ?
Ans. EcoRI is a restriction endonuclease enzyme, that is Ans. These are special proteins which are insecticidal in
extracted from bacterium E.coli. It differs from nature. These are produced by a bacterium — Bacillus
exonuclease because, exonuclease makes peripheral thuringiensis.
cuts, whereas EcoRI, being endonuclease makes Q.7. Define genetic engineering.
internal cuts at precise points. Ans. Genetic engineering is the manipulation of genetic
Q.3. Why is Taq polymerase preferred in PCR ? Mention material of an organism in order to produce desirable
the source of this enzyme. changes.
Ans. It is a thermostable DNA polymerase that is obtained Q.8. What is the purpose of electrophoresis ?
from a bacterium Thermus aquaticus. Ans. Electrophoresis is carried out to arrange charged
Q.4. Name the source of the DNA polymerase used in PCR particles according to their size.
technique. Mention why it is used? Q.9. What is recombinant DNA ?
 96

Ans. Recombinant DNA is the DNA formed by combining Q.12. Mention the uses of cloning vector in biotechnology.
DNAs from two different organisms. Ans. Cloning vectors are used for transferring fragments of
Q.10. Wrtie the name and functions of any two enzymes foreign DNA into a suitable host. They are also used to
useful in genetic engineering. (2017) select recombinants from non-recombinants.
Ans. The two useful enzymes in genetic engineering are Q.13. Recombinant DNA was first created by whom?
restriction endonucleases and DNA ligases. Ans. First recombinant DNA was created by Stanley Cohen
The function of restriction endonuclease is to form and Herbert Boyer in 1972.
recombinant DNA molecules which are composed of Q.14. How recombinant DNA is formed? (2011)
desired genes. DNA ligases are used to join Ans. Recombinant DNA is formed by combining DNA
complementary DNA strands/ends together. molecules from two different sources by gene cloning
Q.11. What are restriction enzymes (molecular scissors)? and gene transfer.
Write down their functions. (2017, 18) Q.15. Write down the name of any cloning vector in which
Ans. Restriction enzymes are molecular scissors which are capacity of replication is present independently
used for cutting DNA at specific locations. These without chromosomal control. (2019)
belong to a larger class of enzymes called nucleases, Ans. Such as cloning vector is plasmid and other cloning
which are of two types : vectors are bacteriophages, SV-40 (for animals),
(i) Endonucleases (ii) Exonucleases Ti-plasmids (for plants) etc.
These enzymes are used to form recombinant DNA
molecules bearing desired gene.

Short Answer Type Questions 2 & 3 Marks

Q.1. How are ‘sticky ends’ formed on a DNA strand? Why (on the gel) are cut from the agarose gel and extracted
are they so called ? from the gel piece. This process is called elution.
Ans. Restriction enzymes cut the two strands of the DNA Q.5. List the key tools used in recombinant DNA
molecule, a little away from the centre of the technology.
palindromic sites, but between the same two bases on Ans. The key tools used in recombinant DNA technology
opposite strands. This leaves called sticky single are:
stranded position at the ends. (i) Restriction enzymes (ii) Polymerase enzyme
These are named so because they form hydrogen bonds (iii) Ligase enzyme (iv) Vectors
with their complementary cut counterparts. (v) Host organism/cell.
Q.2. Why are molecular scissors so called? Write their use Q.6. Explain the action of the restriction endonuclease
in biotechnology. EcoRI.
Ans. Molecular scissors are so called because they cut the Ans. (i) The recognition sequence shows palindrome
DNA at very specific and precise sites. They cut the character in which the sequence of base pairs read
DNA and produce sticky ends. the same on both the DNA strands, i. e., same in 5¢
With the help of these enzymes, DNA from two ® 3¢ or 3¢ ® 5¢ directions, e. g., 5¢ — GAATTC —
different sources can be cut and recombine with each 3¢ or 3¢—CTTAAG —5¢
other. Therefore these enzymes are helpful in (ii) The restriction endonuclease acts on specified
producing recombinant DNA. length of a DNA and binds to the DNA at the
Q.3. Name the natural source of agarose. Mention one role recognition sequence.
of agarose in biotechnology. (iii) It cuts the opposite double helix of DNA in the
Ans. The natural source of agarose is sea weed. Agarose is a sugar-phosphate backbones, at little away from
natural polymer. It is used to develop the matrix for gel the centre of the palindrome sites.
electrophoresis, which helps in the separation of DNA (iv) There are overhanging stretches called sticky
fragments in an electric field, based on their size. ends on each strand, which form hydrogen bonds
Q.4. How can DNA segments, separated by gel with their complementary cut counterparts. This
electrophoresis, be visualised and isolated ? stickiness of the ends facilitates the action of the
Ans. The separated DNA molecules are visualised only after enzyme DNA ligase.
staining DNA with ethidium bromide followed by Q.7. Write the role of ‘Ori’ and ‘restriction’ site in a cloning
exposure to UV radiation. They appear as bright vector pBR322.
orange coloured bands. The separated bands of DNA
 97

Ans. ‘Ori’ is the site where replication starts. This site is (ii) Ori and rop genes
responsible for controlling the copy number of a (iii) amp (an antibiotic resistant gene)
Eco RI
vector. Restriction site is the site of ligation of Bam HI
alien/foreign DNA in the vector, in one of the two ampR
antibiotic resistance site or coding sequence of a pBR322
galactosidase.
Q.8. List the steps involved in recombinant DNA
ori rop
technology.
Ans. Steps in recombinant DNA technology : Fig. E. coli cloning vector pBR322
(i) Isolation of DNA.
Q.12. Comment on gel electrophoresis. (2018)
(ii) Fragmentation of DNA by restriction
Ans. DNA fragments are separated on the basis of their size
endonucleases.
by a provalent technique. This technique is called gel
(iii) Isolation of the desired DNA fragments.
electrophoresis. DNA fragments are negatively
(iv) Amplification of the gene of interest.
charged molecules, so they are separated by moving in
(v) Ligation of the DNA fragment into a vector using
gel medium in the electric field towards the anode. The
DNA ligase.
smaller DNA segments, the far they travel.
(vi) Transfer of recombinant DNA into the host
Q.13. (i) How are recombinant vectors created?
organism.
(ii) For creating one recombinant vector only one
(vii) Culturing the host cell on a suitable medium on a type of restriction endonuclease is required. Give
large scale. reason.
(viii) Extraction of the desired product. Ans. (i) The vector DNA is cut at a particular restriction
(ix) Downstream processing of the products as site using a restriction enzyme (to cut the desired
finished products are ready for marketing. DNA segment). The alien DNA is then linked
Q.9. What is GMF (Genetically Modified Food) ? with the plasmid DNA using an enzyme called
Ans. To improve crop productivity and their resistance for ligase to form the recombinant vector.
pests, scientists are now modifying their genetic (ii) Since a restriction enzyme recognises and cuts the
makeup with the help of genetic engineering. The food DNA at a particular sequence is called recognition
from such genetically engineered plants and crops is site, the same restriction enzyme is used for
called GMF (Genetically Modified Food). cutting the DNA segment from both the vector
Q.10. Study the linking of DNA fragments shown below : and the other source.
a DNA b DNA
Q.14. Write note on genetic engineering. (2018)
A A T T C Ans. It is the process of manipulation of genetic material of
G living organisms (animals, plants and microbes) by
man in vitro for the benefit of mankind. An example of
G
genetic engineering technique is Recombinant DNA
C T T A A Technology (RDT), which aims are isolating desired
(i) Name ‘a’ DNA and ‘b’ DNA. DNA sequences from different sources and then
(ii) Name the restriction enzyme that recognises this joining them to produce a recombinant DNA.
palindrome. Q.15. Give the name of the type of bioreactor shown in given
(iii) Name the enzyme that can link these two DNA figure. Write the purpose for which it is used.
fragments.
Ans. (i) ‘a’ is vector/plasmid DNA, ‘b’ is foreign DNA
pH Motor
(ii) EcoRI Controller
(iii) DNA ligase. Foam braker
Q.11. Draw a schematic sketch of pBR322 plasmid and label
Steam for
the following in it sterilisation
Impeller
(i) Any two restriction sites
Culture
(ii) Ori and rop genes broth
(iii) An antibiotic resistant gene
Ans. The labelled diagram of pBR322 plasmid is shown in
the given figure with— Sterile air
(i) EcoRI and Bam HI as restriction enzymes
 98

Ans. The given bioreactor shown in the figure is the simple (ii) Primers : These are chemically synthesised
stirred-tank type bioreactor. Its purpose is large scale oligonucleotides (short segment of DNA) that are
production of recombinant proteins or enzymes, using complementary to the regions of DNA template.
microbial plants, animals and human cells. (iii) Enzymes : Two commonly used enzymes in PCR
Q.16. Write four applications of genetic engineering. (2018) reaction are—
Ans. Four applications of genetic engineering are as Taq Polymerase : It is isolated from a
follows: thermophilic bacterium, i. e., Thermus aquaticus.
(i) Mapping of human gene It has a property to remain active during the high
(ii) Idendify of individual genes temperature induced denaturation of double-
(iii) Detect of genetic disease stranded DNA. It also helps in the amplification of
(iv) Treatment of genetic disease a segment of DNA.
Q.17. What are plasmids? Write their utility in the life of Vent Polymerase (isolated from Thermococcus
living organisms. (2007, 09) litoralis).
Or Write four main characters of plasmids. Nucleotide Bases : These are added by DNA
(2007, 08, 11, 16) polymerase to the growing chain.
Or Where are plasmids found? Where are they used? Three main steps involved in the PCR technique are—
Or Explain plasmid. Mention their uses. Step I (Denaturation) : The double-stranded DNA is
(2009, 10, 11, 12) denatured by using high temperature of 95°C for
Or Write a short note on plasmid. (2018, 20) 15 seconds. Now, each separated single strand
Ans. Plasmids are extrachromosomal, self-replicating, acts as a template for DNA synthesis.
double-stranded, closed and circular DNA molecules. Step II (Annealing) : Two sets of oligonucleotide
These are seen in the bacterial cells and few yeast cells. primers are annealed (hybridised) to the separated
These are used as vectors in biotechnology. single-strands. This step is carried out at a slightly
Characters of plasmids : lower temperature ( 40 - 60°C).
(i) They are inherited independently. Step III (Extension) : The thermostable enzyme Taq
(ii) They contain antibiotic resistant genes on them. DNA polymerase is used in this reaction, extends
(iii) They have capacity to replicate independently the primers by adding dNTPs
from host cell.
(deoxynucleoside triphosphates) complementary
Plasmids are useful for molecular biologists because
to those of the template DNA.
these scientists can form a desired cell by using 2+
Mg is required as a cofactor for thermostable DNA
plasmids as genetic vectors and inserting them in the
desired cell. When desired gene is inserted in plasmid polymerase. These steps are repeated many times in
and these modified plasmids are placed inside the host order to obtain several copies of desired DNA.
cell, they start replicating with the population of
bacteria, which was descend from the ancestor host Region to be amplified

cell. If such genes code for protein like Thyroid 5´ 3´

Stimulating Hormone (TSH), the proteins accumulate 3´ 5´
inside the bacterium, from where it can be extracted. Heat (causes separation Denaturation
1. of strands)
Therefore, 20 such plasmids can be placed in E. coli.
Cycle repetition

Primer
As a result, 20 TSH genes can be placed at a time and 5´ 3´
3´ 5´
these genes can collectively produce 20 time more
5´ 3´
quantity of this hormone. 3´ 5´
Primer DNA polymerase Annealing of
Q.18. Explain polymerase chain reaction (PCR) with the help (Tag polymerase) primers
of diagram. (2019) 2. + deoxynucleotides
5´ 3´
Or Write a short note on PCR. (2019) 3´ 5´

Ans. Polymerase Chain Reaction (PCR) : It is best 5´ 3´

3´ 5´
defined as in vitro process of DNA replication. This Extension
technique was developed by Kary Mullis in 1985, who 30 cycles (polymerisation)
3.
received Nobel Prize for it in 1993.
The basic requirements of a PCR reaction are as
Amplified DNA
follows : (~1 billion times)
(i) DNA Template : The double-stranded DNA that Polymerase Chain Reaction (PCR)
needs to be amplified.
 99

Q.19. What do you know about gel electrophoresis? Describe (ii) DNA ligase : See the answer of Short answer type
in brief the technique of separation and isolation of question-24.
DNA fragment. (2019) Q.23. What is the importance of cloning vectors in
Ans. DNA fragments are separated on the basis of their size biotechnology? (2019)
by a provalent technique. This technique is called gel Ans. Decades after their first use, plasmids are still crucial
electrophoresis. laboratory tools in Biotechnology. Virtually all
Since, the DNA fragments are negatively charged plasmids that are used to deliver DNA contain genes
molecules, so they can be separated by forcing them to for antibiotic resistance. Cloning vectors are used as
move towards the anode under an electric field through the vehicle for transporting foreign genetic material
a medium or matrix (agarose). into another cell. This foreign segment of DNA is
The smaller the fragment size, farther it moves. The replicated and expressed using the machinery of the
separated DNA fragments can be visualised only after host organism. A cloning vector facilitates
staining the DNA with Ethidium Bromide (EtBr) amplification of a single copy DNA molecule into
followed by exposure to UV radiation. The bright many capies.
orange coloured bands of DNA, are seen when exposed All commonly used cloning vectors in molecular
to UV light. biology have key features necessary for their function,
These stained separate bands of DNA are cut out from such as suitable cloning site and selectable marker.
the agarose gel and extracted from the gel piece by the Thus the cloning vectors used often have elements
process known as elution. necessary for their propagation and maintenance in
Q.20. Write short notes on the following : (2019) E . coli, such as a functional origin of replication (ori).
(i) Bioreactor Q.24. What are restriction enzymes? Write down their
(ii) DNA polymerase enzyme functions. (2018, 20)
Ans. (i) Bioreactor : Please see NCERT Que. 10(b). Or What do you mean by restriction enzyme. Explain
(ii) DNA polymerases are enzymes that play a key its significance. (2020)
role in DNA replication. DNA replication is the Or Explain the ‘restriction enzyme’ in brief and write
process of splitting an existing double-stranded down the name of two type restriction enzyme also.
DNA molecule into two single strands of DNA, (2020)
then using DNA polymerases to translate the Ans. Restriction enzymes are molecular scissors which are
single strands. used for cutting DNA at specific locations. These
The function of DNA polymerase is to replicate, belong to a larger class of enzymes called nucleases,
proofread and repair DNA. Several DNA which one of two types :
polymerases exist, but DNA polymerase I, or Pol (i) Endonucleases (ii) Exonucleases
I, and DNA polymerase III or Pol III, are the main These enzymes are used to form recombinant DNA
ones involved in DNA replication. molecule bearing desired gene.
Q.21. What are exonucleases and endonucleases? Write their Q.25. Write down the functions of restriction enzyme and
functions. (2019) ligase enzyme. (2020)
Ans. Exonucleases and Endonucleases : Please see Ans. Functions of restriction enzyme :
NCERT question-12. (i) They are used to assist insertion of genes into
Functions : Exonuclease act on single strand of DNA plasmid vectors during gene cloning and protein
or gaps in double stranded DNA. Endonuclease cleave production experiments.
one strand or both strands of double stranded DNA. (ii) Restriction enzymes can also be used to
They also called molecular scissors. distinguish gene alleles by specifically
Q.22. Write short notes on the following : recognising single base changes in DNA.
(i) RNA Polymerase (ii) DNA ligase Functions of Ligase enzyme :
Ans. (i) RNA Polymerase : A RNA polymerase (RNAP) (i) DNA ligase is an enzyme which can connect two
or ribonucleic acid polymerase, is a multi subunit strands of DNA together by forming a bond
enzyme that catalyzes the process of transcription between the phosphate group of one strand and
where an RNA polymerase is synthesized from a the deoxyribose group on another.
DNA template. (ii) It is used in cells to join together the Okazaki
Transcription begins when RNA polymerase fragments which are formed on the laggign strand
binds to a promoter sequence near the beginning during DNA replication.
of gene (directly or through helper protein).
100

Long Answer Type Questions 5 Marks

Q.1. Briefly describe DNA recombinant techniqe and write (iii) Selectable Marker : It helps in identifying or
characteristic feature of pBR322 vector with a selecting transformants and eliminating
well-labelled diagram. (2014, 15) non-transformants by selectively permitting the
growth of the transformants.
Ans. DNA Recombinant technique : Please see answer of
Transformation is a procedure, through which a
Long answer question-2.
piece of DNA is introduced into the host
Characteristic features of pBR 322 : pBR 322 is the bacterium. Normally, the genes encoding
standard cloning vector obtained from E. coli. It is resistance to antibiotics like ampicillin,
genetically engineered and has one or two genes for chloramphenicol, tetracycline, kanamycin, etc.,
resistance against antibiotics. It is a plasmid vector, i. e. are considered as useful selectable markers for E.
extrachromosomal, self-replicating, double-stranded coli. The normal E. coli cells do not carry
closed and circular DNA present in E. coli. It’s name resistance against any of these antibiotics.
was given by Bolivar and Rodriguez. Therefore, its Q.2. Write a note on gene cloning : (2020)
name is pBR322. It has 4361 base pairs. Ans. The production of exact copies of a particular gene or
Features that are required to facilitate cloning into a DNA sequence using genetic engineering techniques is
pBR322 vector are— called gene cloning.
(i) Origin of replication (Ori) : This is a sequence The term “gene cloning,” “DNA cloning,”
“molecular cloning,” and “recombinant DNA
from where replication starts and any piece of
technology” all refer to same technique.
DNA when linked to this sequence can be made to
DNA cloning can be achieved by two different
replicate within the host cells. This sequence is methods :
also responsible for controlling the copy number (i) Cell based DNA cloning
of the linked DNA. (ii) Cell-free DNA cloning (PCR)
(ii) Cloning (Recognition) Sites: These are generally Principle of Gene Cloning
required to link the foreign or alien DNA with the A fragment of DNA, containing the gene to be cloned,
vector. For this, the vector requires very few or is inserted into a suitable vector, to produce a
single recognition sites for commonly used recombinant DNA molecule. The vector acts as a
restriction enzymes. If more than one recognition vehicle that transports the gene into a host cell usually a
sites is present within the vector, it will generate bacterium, although other types of living cell can be
several fragments that will lead to more used. Within the host cell the vector multiplies,
complication in gene cloning. producing numerous identical copies not only of itself
Cal I Hind III
Eco R I
but also of the gene that it carries. When the host cell
Bam H I
Pvu I divides, copies of the recombinant DNA molecule are
passed to the progeny and further vector replication
Pst I
takes place. After a large number of cell divisions, a
ampR tetR colony, or clone, of identical host cells is produced.
pBR322 Sat I
Each cell in the clone contains one or more copies of
ori rop the recombinant DNA molecule; the gene carried by
the recombinant molecule is now said to be cloned.
Steps used in Gene Cloning
Pvu II The basic steps involved in gene cloning are :
Fig. E. coli cloning vector pBR322 (a) Isolation of the DNA fragment or gene
The ligation of the foreign DNA is carried out at a The target DNA or gene to be cloned must be first
restriction site present in one of the two antibiotic isolated. A gene of interest is a fragment of gene whose
resistance genes. Selection of recombinants product (a protein, enzyme or a hormone) interests us.
formed can be done by one of the following For example, gene encoding for the hormone insulin.
methods, given below : The desired gene may be isolated by using restriction
· Inactivation of antibiotic resistance gene. endonuclease (RE) enzyme, which cut DNA at specific
· Insertional activation. recognition nucleotide sequences.
 101

E. coli bacterium (e) Isolation of Recombinant Cells

Plasmld Cell with DNA
containing gene For isolation of recombinant cell from
1 Isolate plasmid of interest
Bacterial Isolate DNA non-recombinant cell, marker gene of plasmid vector is
chromosome 2
employed.
3 Cut plasmid DNA
For examples, pBR322 plasmid vector contains
wlth enzyme Gene of interest
4 Cut cell’s DNA
different marker gene (Ampicillin resistant gene and
Gene
with same enzyme Tetracycline resistant gene. When pst1 RE is used it
of interest knock out Ampicillin resistant gene from the plasmid,
5 Combine targeted fragment so that the recombinant cell become sensitive to
and plasmid DNA Ampicillin.
(f) Multiplication of Selected Host Cells
6 Add DNA ligase, which closes
the circle with covalent bonds Once transformed host cells are separated by the
Recombinant screening process; becomes necessary to provide them
Gene of interest
DNA plasmid optimum parameters to grow and multiply.
7 Put plasmid into bacterium In this step the transformed host cells are introduced
by transformation
into fresh culture media.
Recombinant
bacterium At this stage the host cells divide and re-divide along
8 Allow bacterium with the replication of the recom-binant DNA carried
to reproduce

Clone by them.
of cells (g) Isolation and Purification of the Product
The next step involves isolation of the multiplied GI
Fig. Steps used in gene cloning
attached with the vector or of the protein encoded by it.
(b) Selection of suitable cloning vector This is followed by purification of the isolated gene
The vector is a carrier molecule which can carry the copy/protein.
gene of interest (GI) into a host, replicate there along Gene for human
Recombinant growth hormone
with the GI making its multiple copies. The cloning EooRI
DNA
vectors are limited to the size of insert that they can
Gene for human
carry. Depending on the size and the application of the growth hormone
insert the suitable vector is selected. DNA
Human cell Sticky
(c) Formation of Recombinant DNA ends
recombination

The plasmid vector is cut open by the same RE enzyme DNA

insertion
used for isolation of donor DNA fragment. The mixture Bacterial cell
Bacterial
of donor DNA fragment and plasmid vector are mixed chromosome EooRI

together. In the presence of DNA ligase, base pairing of

donor DNA fragment and plasmid vector occurs.
Bacterial cell for
The resulting DNA molecule is a hybrid of two DNA containing gene for
Plasmid
molecules – the GI and the vector. In the terminology human growth hormone

of genetics this intermixing of different DNA strands is Applications of Gene Cloning

called recombination. (i) A particular gene can be isolated and its
Hence, this new hybrid DNA molecule is also called a nucleotide sequence determined.
recombinant DNA molecule and the technology is (ii) Control sequences of DNA can be identified and
referred to as the recombinant DNA technology. analyzed.
(d) Transformation of recombinant vector into suitable (iii) Protein/enzyme/RNA function can be
host investigated.
The recombinant vector is transformed into suitable (iv) Mutations can be identified, e. g., gene defects
host cell mostly, a bacterial cell. Some bacteria are related to specific diseases Organisms can be
naturally transformable; they take up the recombinant ‘engineered’ for specific.
vector automatically. (v) Purposes, e. g., insulin production, insect
For example: Bacillus, Haemophillus, Helicobacter resistance, etc.
pylori, which are naturally competent.
 102

NCERT Fully Solved Exercise

Q.1. Can you list 10 recombinant proteins/products, which Ans. A chromosome contains one DNA molecule. So, these
are used in medical practice? Find out where they are are 46 DNA molecules in a normal human cell (G1
used as therapeutics. phase).
Ans. Q.5. Do eukaryotic cells have restriction endonucleases?
Human insulin Treatment of insulin dependent Justify your answer.
diabetes Ans. Restriction endonucleases are not found in eukaryotic
Human growth hormone Treatment of growth hormone cells. Till date, all restriction enzymes have been
related disorders isolated from bacterial cell (which are prokaryotic).
Calcitonin Treatment of rickets Q.6. Besides better aeration and mixing properties, what
Chorionic gonadotropin Treatment of infertility other advantages do stirred tank bioreactors have over
Blood clotting factor VIII/IX Treatment of haemophilia shake flasks?
Tissue Plasminogen Dissolving blood clots after heart Ans. Stirred tank bioreactors have systems for pH,
Activator attacks and strokes temperature control. They also have foam control
Erythropoetin Stimulation of RBC production in systems and sampling ports. All these features make
anaemic persons these bioreactors advantageous over shake flasks.
Platelet derived growth factor Stimulation of wound healing Q.7. Collect 5 examples of palindromic DNA sequences by
Interferon Treatment of viral infections consulting your teacher. Better try to create a
palindromic sequence by following base-pair rules.
Interleukins Enhancement of immune response
Ans.
Vaccines Prevention of infectious diseases
Palindromic Enzyme Source
Q.2. Make a chart (with diagrammatic representation) Recognition Site
showing a restriction enzyme, the substrate DNA on G¯ AATT C EcoRI Escherichia coli R factor
which it acts, the site at which it cuts DNA and the C TTAA­ G
product it produces. G¯ GATC C BamHI Bacillus amyloliquefaciens
Ans. The required chart (diagram) for EcoRI is given below:
C CTAG­ G
5´ 3´ GG¯ CC HaeIII Hemophilus aegyptius
CC­ GG
3´ 5´ A¯ AGCT T HindIII Hemophilus influenzae D
T TCGA­ A
T¯ CG A TaqI Thermus aquaticus
5´ 3´ A GC­ T

3´ 5´ Q.8. Can you recall meiosis and indicate at what stage a

recombinant DNA is made?
Ans. In a normal cell, dividing by meiosis, a recombinant
DNA is made during crossing over. It occurs during
5´ 3´
prophase I stage.
Q.9. Can you think and answer how a reporter enzyme can
3´ 5´
Product (cut DNA pieces)
be used to monitor transformation of host cells by
foreign DNA in addition to a selectable marker ?
Q.3. Can you tell whether enzymes are bigger or DNA is Ans. A reporter enzyme is produced by a reporter gene,
bigger in molecular size? How did you know? which can be used to monitor the transformation of
Ans. DNA is bigger than enzyme in length. This is because, host cells by foreign DNA. Such a reporter gene, along
one enzyme works on one palindromic site. A DNA with the foreign gene is placed in the same DNA
can have many such sites. This shows that the size of construct. Then, this combined DNA construct is
DNA is bigger than that of an enzyme. inserted into the cell. Here, the reporter gene is used as
Q.4. What would be the molar concentration of human a selectable marker to find out the successful uptake of
DNA in a human cell? genes of interest (foreign genes). If the transformation
is successful, the reporter gene would produce the
 103

reporter enzyme. So, the presence of reporter enzyme which are also called molecular scissors, are being
in the host cell clearly indicates the successful used in DNA recombination technology.
transformation. (c) Chitinase: It is an hydrolytic enzyme which is
Q.10. Describe briefly the following : used to digest a complex polysaccharide, chitin,
(a) Origin of replication (b) Bioreactors which is often found in the cell wall of fungi. So,
(c) Downstream processing in order to isolate the DNA enclosed within the
Ans. (a) Origin of replication: Origin of replication is cell membrane of the fungus, enzyme chitinase is
defined as the DNA sequence in a genome from used to break the cell for releasing its genetic
where replication is started. The initiation of material.
replication is usually bidirectional. A protein Q.12. Discuss with your teacher and find out how to
complex recognizes the ‘on’ site, unwinds the two distinguish between :
strands, and initiates the DNA replication. (a) Plasmid DNA and Chromosomal DNA
(b) Bioreactors: Bioreactors are large glass or steel (b) RNA and DNA
vessels, used for the large-scale production of (c) Exonuclease and Endonuclease
microbial products from raw materials. They Ans. (a) Plasmid DNA and Chromosomal DNA
provide optimal conditions of growth for Plasmid DNA Chromosomal DNA
microorganisms in order to obtain the desired Plasmid DNA is an Chromosomal DNA is the main
product. Bioreactors have an oxygen delivery extra-chromosomal DNA chromosomal DNA. It contains
system, a foam control system, a pH and molecule in bacteria which genes for all important activities of
temperature control system, and a sampling port can replicate independently. the cell.
It has genes for antibiotic
to obtain a small volume of culture for sampling. resistance.
For diagram please see the answer of Short answer
the question-15. (b) RNA and DNA
(c) Downstream processing: Downstream RNA DNA
processing is a method of separation and RNA is a single stranded DNA is a double stranded molecule.
purification of foreign gene products after the molecule.
completion of the biosynthetic stage. The product It contains ribose sugar. It contains deoxyribose sugar.
is subjected to various processes in order to RNA does not contain DNA does not contain Uracil but
separate and purify the product. After thymine but contain uracil. contain Thymine.
downstream processing, the product is formulated RNA cannot replicate itself. DNA molecules can replicate by
and is passed through various clinical trials for itself.
quality control and other tests. It is a component of the It is a component of the
Q.11. Explain briefly : ribosomes. chromosomes.
(a) PCR It does not follow Chargaff’s It does follows Chargaff’s base
(b) Restriction enzymes and DNA base pairing rule. pairing rule.
(c) Chitinase (c) Exonuclease and Endonuclease
Ans. (a) PCR or polymerase chain reaction: See the
Exonuclease Endonuclease
answer of Short answer type question-18.
It is a type of restriction It is a type of restriction enzyme that
(b) Restriction enzymes: These are specific enzyme that removes the makes a cut within the DNA to
endonuclease enzymes which can cut a DNA nucleotide from 5’ or 3’ ends generate sticky ends.
molecule at a very precise site (called of the DNA molecule.
palindromic/restriction site). These enzymes,

ccc
 104

Chapter

12
BIOTECHNOLOGY
AND ITS
APPLICATIONS

² Totipotency of animal cells is lost due to a high degree of specialisation and differentiation.
² Transgenic crops give rise to genetically modified food (GMF).
² Super mouse is a transgenic mouse, which has been produced by inserting human growth hormone forming gene into mouse
genome. It is double the size of a normal mouse.
² CC Kitten was the first cloned cat.
² The first clinical gene therapy was given in 1990 to a 4-year old girl. She had genetic deficiency of an enzyme adenosine
deaminase (which is responsible for normal functioning of immune system).
² Insulin is synthesized from the proinsulin precursor molecule by the action of proteolytic enzymes, known as prohormone convertases
(PC1 and PC2), as well as the exoprotease carboxypeptidase enzyme.
² Bacillus thuringiensis, or Bt, is an endospore forming bacterium.
² Bt cotton is resistant to the attack of worms.
² Bt in Bt crops refers to Bacillus thuringiensis.
² Bt toxin is produced by a bacterium called Bacillus thuringiensis.
² Bacillus thuringiensis is a bacterium that produces ‘cry protein’.
² The Bt toxin protein does not kill the bacteria itself because it exists as inactive protoxins but once an insect ingests the inactive toxin, it
is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the
surface of midgut epithelial cells and causes their lysis (breakdown), finally, resulting in the death of the larvae.
² Insulin consists of two short polypeptide chains: chain-A and chain-B, that are linked together by disulphide bridges.

Multiple Choice Questions 1 Mark

Q. 1. Recombinant DNA is also called: (a) GM-Tomato (b) GM-cotton

(a) Pseudo DNA (b) Sat DNA (c) Disease (d) Transgenic pig
(c) Chimeric DNA (d) cDNA Q. 6. Maximum number of existing transgenic animals is of:
Q. 2. The enzymes which are commonly used in genetic (a) Cow (b) Pig
engineering are: (c) Fish (d) Mice
(a) Restriction endonuclease and polymerase Q. 7. The first human produced by r-DNA technology:
(b) Endonuclease (a) Progesterone (b) Insulin
(c) Restriction endonuclease and ligase (c) Estrogen (d) Thyroxin
(d) Ligase and polymerase. Q. 8. Natural genetic engineer is:
Q. 3. Cry genes are found in: (a) Bacillus subtilis
(a) Agrobacterium (b) Bacillus thuringiensis (b) Pseudomonas sp.
(c) Rhizobium (d) T2 bacteriophage (c) Escherichia coli
Q. 4. If other one or more genes are introduced in any plant, (d) Agrobacterium tumefaciens
the plant will be called: (2017) Q. 9. Which one of the following can be used as a vector in
(a) Transgressive (b) Transgenic DNA recombination technology?
(c) Triploid (d) Trisomic (a) Phasmid (b) Plasmid
Q. 5. Flavr Savr is a: (c) Cosmid (d) All of these
 105

Q.10. Which of the following takes part in the production of Q.14. Bt-toxin is produced by which bacteria? (2019)
Bt crops ? (2017) (a) Bacillus vulgaris (b) Bacillus thuringiensis
(a) Algae (b) Fungi (c) Bacillus subtilis (d) Bacillus megatherium
(c) Bacteria (d) All of these Q.15. Which statement is correct for genetic modification?
Q.11. Bt cotton has an insecticidal property which is a type (2020)
of: (2017) (a) Genetically modification made crops more
(a) Carbohydrate (b) Lipid tolerent to drought and cold.
(c) Protein (d) Vitamin (b) Genetic modification reduced reliance on
Q.12. Which of the following is obtained from genetic chemical pesticides.
engineering? (2017) (c) Genetic modification enhanced nutritional value
(a) Golden rice (b) Maize of food.
(c) Wheat (d) Glucose (d) All of these.
Q.13. Which of the following synthesis of substance by Q.16. Genetic engineering is used in : (2020)
genetic engineering on the industrial level? (2018) (a) Agriculture field
(a) Human growth hormone (b) Medical field
(b) Insulin (c) Vaccine manufacturing
(c) Interferon (d) All of these
(d) All of the above

Answers
1. (c) 2. (c) 3. (b) 4. (b) 5. (a) 6. (b) 7. (b) 8. (d) 9. (b) 10. (c)

11. (c) 12. (a) 13. (d) 14. (b) 15. (d) 16. (d)

Very Short Answer Type Questions 1 Mark

Q.1. What is recombinant DNA? Ans. It is a transgenic cotton plant. It has been developed by
Ans. Recombinant DNA is the DNA formed by combining inserting gene from Bacillus thuringiensis bacterium.
DNAs from two different organisms. Due to this, the plant is resistant to the attack of
Q.2. What is gene gun? worm/pathogens.
Ans. The instrument for bombarding micro-projectile Q.8. Give the full form of SCID and ELISA.
particles (gold/tungsten particles) coated with foreign Ans. SCID— Severe Combined Immuno Deficiency.
DNA, with great velocity, into a target cell is called ELISA— Enzyme Linked Immuno-Sorbent Assay.
gene gun. Q.9. Write two uses of PCR technique in diagnosis.
Q.3. What are cry proteins? Ans. (i) It is used to increase the amount of DNA during
Ans. These are special proteins which are insecticidal in forensic investigation.
nature. These are produced by a bacterium-Bacillus (ii) It helps to obtain multiple copies of a particular
thuringiensis. gene for DNA recombination experiments.
Q.4. Name the substance used as a medium in gel Q.10. What are transgenic animals?
electrophoresis? Ans. Animals in which, DNA has been manipulated to
Ans. Agarose. possess and express an extra gene are known as
Q.5. What is a plasmid? transgenic animals.
Ans. A plasmid is a circular extra-chromosomal DNA Q.11. Which vitamin is found in more quantity in golden rice
molecule present in a bacterial cell, which is used as a obtained by genetic engineering? (2017)
vector in r-DNA technology. Ans. Vitamin A (b-carotene).
Q.6. Define genetic engineering. Q.12. Write two uses related to Agriculture of
Ans. Genetic engineering is the manipulation of genetic Biotechnology? (2018)
material of an organism in order to produce desirable Ans. (i) Development of resistance species.
changes. (ii) Increase in plant yield.
Q.7. What is Bt cotton?
Q.13. What is Interferon? (2018)
 106

Ans. Interferon is an antivirus glycoprotein. They are Ans. See short answer type question no. 1.
working as immunity controller. It is using in treatment Q.15. What is Biopiracy? (2020)
of many diseases now-a-days. Ans. Please see the answer of Short answer type question-3.
Q.14. What do you understand by transgenic (GMO)
animals? (2014)

Short Answer Type Questions 2 & 3 Marks

Q.1. Write short note on the following: transgenic. In other words, transgenic bacterium are
(i) GMOs (2018) (ii) Recombinant DNA (2020) those, whose genomes have been changed due to the
Ans. (i) GMOs: The organisms in which the genes have presence of other species genes.
been changed by manipulation are called as e. g., In 1983, insulin was produced by inserting
genetically modified organisms (GMOs). These recombinant plasmid in E.coli, preparing two DNA
are the organisms in which the foreign genes have sequences corresponding to the sequence of human
been introduced by genetic engineering methods. insulin A and B.
The foreign genes change the expression of such Q.3. Comment on the following :
organism genetically. The GMOs are therefore (i) Biopiracy (2014, 15, 18) (ii) Biopatent
also called as Transgenic organisms and the genes Ans. (i) Biopiracy: If multinational companies or other
which are introduced are known as transgenes. organisation uses the bioresources or traditional
(ii) Recombinant DNA: Recombinant DNA knowledge of any country or from their people
technology is a stream of biotechnology which without authorized or without any compensation,
deals with the manipulation of genetic material by it is known as biopiracy.
man in vitro, in which the desired genes or DNA (ii) Biopatent: Biopatent refers to patents obtained
sequence of an organism are cut into fragments by individual/groups/country to establish
and then introduced into host cells with or without exclusive right over the origin of a particular
help of carrier or vectors to alter its phenotype to organism/plants. Such rights gives the holder to
suit human needs. claim global trading rights without any other
GAATTC group claiming the trading right.
TAAG
CT Q.4. What is gene therapy? (2009, 14)
DNA to be cloned
Plasmid
cloning GAATTC GAATTC Or Write a short note on gene therapy. (2020)
vector CTTAAG CTTAAG Ans. Gene therapy is a collection of methods that allows
correction of a gene detect that has been diagnosed in a
Eco RI child/embryo. Normally there is no cure for genetic
Eco RI disorder, but gene therapy gives a ray of hope. Here the
AAT defective gene is either corrected or replaced with the
T AATTC G
A G
G TA
C

G CTTAA normal one into the person’s cells and tissues to treat
CT

the disease. A carrier called a vector must be used to

deliver the therapeutic gene to the patient's target cells.
The first clinical gene therapy was given in 1990 to a
Mix together and allow 4-year old girl. The success of gene therapy depends
to hybridize; ligate
using DNA ligase upon the successful transfer of the introduced gene into
(Annealing) the genome of the patient.
Q.5. Write short notes on the following :
(i) Ti-plasmid (ii) Bt-cotton (2020)
Ans. (i) Ti-plasmid: A bacterium (Agrobacterium
tumefaciens) is of common occurrence in the soil.
It causes tumours in dicotyledonous woody plants
which are called as crown galls. The formation of
Recombinant plasmid
tumour is induced due to Ti (Tumour inducing)
Q.2. What is transgenic bacteria? Give an example. plasmid of this bacterium. The tumour causing
Ans. When any gene is inserted into a bacterium then it is part of this plasmid is eliminated and in its place
called transgene and such bacterium is called the genes of desired traits are added. The
 107

recombinant Ti-plasmid formed in this way can be surface proteins. The agent stimulates the body’s
introduced into the bacterial cell with which the immune system to recognise the agent as a threat,
plant cells are again got infected. destroy it, and to further recognize and destroy any of
(ii) Bt-cotton: The bacterium Bacillus thuringiensis the microorganisms associated with that agent that it
produces a kind of protein which has the capacity may encounter in the future.
to kill different types of insects. The genes coding Vaccine can be prophylactic (to prevent or ameliorate
for the Bt-toxin are isolated and introduced into the effect of a future infection by a natural or ‘wild’
the crop plants and in this way Bt-cotton crop pathogen) or therapeutic ( e. g., vaccines against cancer,
plants have been developed. There is no effect of which are being investigated).
boll worms on Bt-cotton and thus the yield Name of two vaccines and their usefulness :
increases. (i) BCG—It is a vaccine used for curing tuberculosis.
Q.6. Describe the medical applications of biotechnology. (ii) Oral Polio Virus (OPV)—It is a vaccine used to
(2017) protect individuals from polio, thus eradicating
Or Write applications of biotechnology in the area of the disease.
human health. (2015, 16) Q.10. Describe the uses of biotechnology in agriculture.
Ans. Health and Biotechnology: Biotechnology has (2019, 20)
specific contribution in the treatment of human Or What is the utility of biotechnology in agriculture?
diseases which are as follows : (2019)
(i) In the production of steroids and insulin hormone. Ans. Please see the ans. of Long answer type question-2.
(ii) In vaccine production. Q.11. What do you mean by Bt? Explain it with example of
(iii) To identify disease during pregnancy. Bt-cotton. (2019)
(iv) To detect AIDS, b-thalassemia, sickle-cell Ans. Bt-meaning is a preparation of a bacterium (Bacillus
anaemia etc. thuringiensis) often modified by genetic engineering
Q.7. Explain gene cloning and cloning of animals and for use as a biopesticide against insects and especially
differentiate between them. (2016) lepidopteran larvae.
Ans. Gene cloning: If many replicas of a single gene or Bt-cotton—Please see the ans. of Short answer type
DNA or chromosome are created, then this action is question-5.
called gene cloning. This practice have become Q.12. What are transgenic animals? Write four benefits of
possible through PCR. such transgenic animals. (2019)
Cloning of animals: It is related to the cloning of Or Write a short note on transgenic animal. (2020)
whole organism. Organism cloning is of two types on Ans. Transgenic animals : The animals in which, DNA has
the basis of its objective or aim. been manipulated to possess and express an extra gene
Q.8. Differentiate between the gene therapy and enzyme are known as transgenic animals.
therapy with example. (2018) Methods for creation of transgenic animals are
Ans. Differences between the gene therapy and enzyme (i) DNA microinjection.
therapy (ii) Embryonic stem cell mediated gene transfer.
Gene therapy Enzyme therapy (iii) Retrovirus mediated gene transfer.
1. In this therapy, faulty It is a medical treatment which Benefits of transgenic animals : Some benefits of
gene is replaced by replaces an enzyme that is transgenic animals are as follows :
functional gene. deficient or absent in the body. (i) These animals have high resistance power.
2. It does not require life It requires life long intravenous (ii) These animals have high yield capacity.
long treatment. infusion. (iii) These animals are highly valuable for agriculture.
3. It cures genetic diseases. Enzyme Replacement Therapy (iv) These animals are highly valuable for industrial
(ERT) cures some lysosomal applications.
storage diseases.
Q.13. What is Bt-toxin? Why does this toxin not kill the
Q.9. What is vaccine? Write the name and usefulness of any Bacillus? (2019)
two vaccines. (2019) Ans. Bt is a kind of anti-toxin produced by a bacteria. Bt
Ans. A vaccine is a biological preparation that provides called Bacillus thuringiensis. Bt gene is isolated from
active acquired immunity to a particular disease. A this bacterium and is transferred to plants by genetic
vaccine typically contains an agent that resembles a engineering. This helps the plants to produce anti-toxin
disease causing microorganism and is often weakened to kill insects/pest causing disease in them. But, Bt
or killed forms of the microbes, its toxins, or one of its
 108

toxin does not kill the Bacillus because toxin is inactive The technique used to make a new combination of
and crystalline form. desired DNA with host to develop the many number of
Q.14. What is biopiracy? Explain it with the help of examples. the exact copies of desired DNA is known as
(2019) recombinant DNA technology.
Ans. Biopiracy refers to the use of bioresources by For the production of insulin with the help of
multinational companies and other organisations Recombinant DNA technology, following steps are
without proper authorisation from the countries and required :
people concerned without any payment. (i) DNA sequences corresponding to the two
All the organisms which can be used to derive polypeptide chains of insulin are synthesised in
commercial benefits are included under bioresources. vitro.
Disputes and accusations are going on about this (ii) They are introduced into plasmid DNA of E.coli.
matter, e. g., efforts by an Australian Government (iii) This bacterium is cloned under suitable
agency in 1997 to preserve Arhar, obtained by conditions.
international gene bank. (iv) The transgene is expressed in the form of
Examples of biopiracy include Basmati seeds, which is polypeptides and secreted into the medium.
an aromatic rice of India. We are growing it since many (v) They are extracted and combined by creating
centuries, but Rice Tech claims that this unique disulphide bridges to form human insulin.
discovery was done by them. In 1996, Dr. Vandana Q.18. What is the importance of biotechnology in human
Shiva challenged the patent granted to the firm of WR life? Explain it in brief ? (2019)
Grace and Co by the European patent office, for Ans. Please see Long answer type question 2.
‘fungicidal uses of neem oil’. Q.19. Write two examples of transgenic organisms. (2019)
Relation with Texmati : In the late 1990’s, a Texas Ans. Examples of two transgenic organisms are given
rice company, Rice Tech claimed to have breed a new below:
variety of Basmati ‘similar or superior to’ Asian (i) Bt-Cotton— Bt toxin gene isolated from bacteria
Basmati. The company was awarded US patent. Rice and transferred to cotton crops, therefore,
Tech planned to market the ‘American Basmati’ under bollworms do not effect Bt-Cotton.
the brand ‘Texmati’. It was an example of high-tech (ii) Golden rice— It is a variety of rice in Vitamin-A.
biopiracy. It is developed by inserting b-carotene genes into
Q.15. Write a short note on vaccine production. (2019) rice plant’s genome.
Ans. Vaccine production : The first step in order to produce Q.20. What is the use of biotechnology in medicines? (2019)
a vaccine is generating the antigen that will trigger the Ans. Please see Long answer type question-2.
immune response. Viruses are grown on primary cells Q.21. Discuss the utility of Gene therapy. (2019)
such as cells from chicken embryos or using fertilized Ans. Please see the NCERT Q.5..
eggs. The hepatitis B and the human papillomavirus Q.22. Write short notes on the following : (2019)
(HPV) vaccine is composed of a protein that resides on (i) Genetically modified crops.
the surface of the virus. It takes a long time to develop a (ii) Application of biotechnology in health.
new vaccine usually between 10 and 15 years. Ans. (i) Genetically modified crops : Genetically
Vaccines go through many phases of development modified crops (GM crops) are plants used in
including research, discovery, pre-clinical testing, agriculture, the DNA of which has been modified
clinical testing and regulatory approval. using genetic engineering methods. In most cases,
Q.16. Define biotechnology. Write the name of only two the aim is to introduce a new trait to the plant
fields where its technique plays an important role in which does not occur naturally in the species.
human welfare. (2019) Examples in food crops include resistance to
Ans. Biotechnology is an integrated branch of biology certain pests, diseases, environmental conditions,
which deals with the techniques of using live organism reduction of spoilage, resistance to chemical
or enzymes from organisms in order to produce treatments (e.g., resistance to a herbicide), or
differnet products and processes useful to humans and improving the nutrient profile of the crop.
See Q.2. (LA). Examples in non-food crops include production
Q.17. Insulin is used for the treatment of which disease? of pharmaceutical agents, biofuels, and other
Describe its method of preparation in brief. (2019) industrially useful goods, as well as for
Ans. Insulin is used for the treatment of Diabetes. bioremediation.
 109

(ii) Application of biotechnology in health : Please extracted and finally combined by creating disulfide
see Short answer type question-6. bonds to form human insulin.
Q.23. Write a short note on stem cell. (2020)
Ans. The key properties of a stem cell were first defined by
Ernest Mc Culloch and James till in the early 1960s.
They discovered the blood forming stem cell, the
hematopoietic stem cell (HSC), through their
pioneering work in mice. In multicellular organisms,
stem cells are un-differentiated or partially
differentiated cells that can differentiate into various
types of cells and divide indefinitely to produce more Fig. Formation of human insulin
of the same stem cell. They are the earliest type of cell Q.25. What are transgenic organisms? Explain with suitable
in a cell lineage. They are found in both embryonic and
examples. (2020)
adult organism, but they have slightly different
Ans. Organisms that have altered genomes are known as
properties in each. They are usually distinguished from
transgenic. Most transgenic organisms are generated in
progenitor cells, which cannot divide indefinitely and
the laboratory for research purposes. For example,
precursor or blast cells, which are usually committed to
“knock-out” mice are transgenic mice that have a
differentiating into one cell type.
particular gene of interest disabled. By studying the
Adult stem cells are found in a few select locations in
effects of the missing gene, researchers can better
the body, known as niches, such as those in the bone
understand the normal function of the gene.
marrow or gonads. They exist to replenish rapidly lost Male pronucleus
cell types and are multipotent or unipotent, meaning
DNA
they only differentiate into a few cell types or one cell
type. Cell
Holding needle
Q.24. Write a short note on human insulin. (2020) Female pronucleus
Ans. Insulin used for diabetes was earlier extracted from Polar bodies
pancreas of slaughtered cattle and pigs. However, this
insulin caused an immune response (allergy) in some
patients.
In mammals, insulin is synthesized in the pancreas
within the beta cells of the islets of Langerhans. Insulin
consists of two short polypeptide chains: chain A and
chain B, that are linked together by disulphide bridges.
Fig. Transgenic mouse
Insulin is synthesized from the proinsulin precursor
molecule by the action of proteolytic enzymes, known Transgenic organisms have also been developed for
as prohormone convertases (PC1 and PC2), as well as commercial purposes. Perhaps the most famous
the exoprotease carboxypeptidase E. These examples are food crops like soy and corn that have
modifications of proinsulin remove the center portion been genetically modified for pest and herbicide
of the molecule, or C-peptide, from the C- and N resistance. These crops are widely known as “GMOs”
terminal ends of the proinsulin. The remaining (genetically modified organisms). Here are few other
polypeptides (51 amino acids in total), the B- and A- examples of transgenic organisms with commercial
chains, are bound together by disulfide/disulphide value:
bonds. So, the C peptide chain is not present in the Golden rice: modified rice that produces b-carotene,
mature insulin. the precursor to vitamin A. Vitamin A deficiency is a
The main problem in developing human insulin by public health problem for millions of people around the
recombination DNA technology, has been getting the world.
insulin in the mature form (i.e., without C peptide). Q.26. What is gene theray? Explain with suitable example.
Eli Lilly (1983), an American company prepared the A (2020)
and B chains separately by introducing DNA Ans. See the answer of question-5 of NCERT excreise.
sequences corresponding to these chains into E. coli
plasmid. The separate chains were isolated and
110

Long Answer Type Questions 5 Marks

Q. 1. What is genetic engineering? Why is this called them with a Ca + + ions which increases the
recombinant DNA technology? Briefly describe DNA efficiency of bacterial cell wall. r-DNA can then
recombination technology. be forced into such cells by incubating the cells
Ans. Genetic Engineering : The genetic engineering or with r-DNA on ice, followed by placing them
recombinant DNA technology is a stream of bio- briefly at 42°C and then putting them back on ice.
technology which deals with the manipulation of 6. Cloning: This is the last step of genetic
genetic material by man in vitro, in which the desired engineering to obtain the several copies of r-RNA.
genes or DNA sequence of an organism are cut into The bacterial cell containing foreign DNA is
fragments and then introduced into host cells with or allowed to grow in DNA culture medium. This
without the help of carriers or vectors to alter its process is called cloning.
phenotype to suit human needs. Q.2. Write down the utility of biotechnology. (2013)
This technique involves the recombination of DNA Or Write down the importance of biotechnology in the
fragments of different organisms, so that it is also field of agriculture. (2015)
called as recombinant DNA technology. Ans. The utility of biotechnology in different fields is as
Process of recombinant DNA technology: It involves follows:
several steps in specific sequence: (i) Biotechnology in agriculture: Some significant
1. Formation of r-DNA: After having cut the source achievements in the field of agriculture by using
DNA as well as the vector DNA with a specific biotechnology are as follows :
restriction enzyme, the cut out gene of interest Development of nitrogen-fixation capacity in a
from the source DNA and cut vector are mixed leguminous plant: Efforts are being done to
and ligase is added. This result in the formation of transfer genetically engineered Nif gene into
recombinant DNA or chimeric DNA. wheat and other leguminous plants by isolating it
2. Amplification of Gene Using PCR: Polymerase form Klebsiella pneumoniae and inserting inside
chain reaction is a technique of synthesizing E. coli.
multiple copies of the desired gene in vitro. It is Protection of plants from diseases: Plants which
based on the principle that a DNA molecule when are produced as a result of culture of meristematic
subjected to high temperature, splits into two tissues, are resistant to viral diseases; e.g., stocks
strands due to denaturation. of sugarcane.
These single stranded DNA molecule in the Development of new species: New species are
presence of DNA polymerase, result in the developed through protoplast fusion (like
duplication of original DNA molecule. Multiple pomato), cloning and other methods.
copies of the DNA can be generated by repeating (ii) Biotechnology in Industry: There are as follows:
process several times. Cheese: Paneer is prepared from fat containing
3. Cutting of DNA at Specific Locations: Restriction milk. Pure milk is heated at 60°C for 30 minutes
enzyme digestions are performed by incubating and at 72°C for 15 minutes. This milk is cooled
purified DNA molecules with the restriction down till 30°C temperature. Thereafter
endonuclease enzyme at the optimal conditions Lactobacillus bacterium and rennin enzymes are
for that specific enzyme. This enzyme only added. About 45 minutes, milk casein becomes
identify the specific palindromes and cut the DNA solid. It is cut into small pieces. These pieces are
molecule from here. heated in hot water for an hour.
4. Isolation of Desired DNA or Gene: This can be These pieces are immersed into light saline water
achieved by treating the cells/ tissue with after carefully squeezing them.
enzymes such as lysozymes. The RNA can be Yoghurt: It is prepared from milk. Now a days it is
removed by treating with ribonuclease, proteins produced at commercial level. For its production,
can be digested by treatment with protease and pure milk is first heated, than cooled, Culture of
purified DNA ultimately precipitates out after the Streptococcus thermophillus and Lactobacillus
addition of chilled ethanol. vulgaris is added in cold state. As a result of this,
5. Insertion of r-DNA into the Host Organism: In milk becomes semi-solid. It gets a smooth
case of bacteria as host this is done by treating substance yoghurt after churning.
 111

Alcohol Production: By using biotechnology Q.3. What is genetic engineering? Describe its application
ethyl alcohol is also produced. in medical. (2020)
It is done by two methods: Or What is recombinant DNA technology? Explain its
(a) By Starchy Substances: Raw material in this uses in human health. (2020)
process is in the form of potato, maize, barley, Ans. Genetic engineering or recombinant DNA
rice, etc. First of all diastase enzyme is obtained technology : See the answer of Long answer
from germinated barley, which is called malt question-1.
extract. Malt is added into boiled starchy Use of genetic engineering in human health :
substance and this is kept at 53°C temperature. Diabetics are unable to produce satisfactory amounts
Diastase enzyme converts starch into maltose. of insulin, which facilitates the processing of sugars
Maltose is boiled to remove diastase enzyme from from food into energy that the body can use. In the past,
it, after that yeast is added into it, after cooling and diabetics needed to take insulin purified from pigs and
kept at 25-37°C. Maltase enzyme degrades cows to fulfill their insulin requirement. However,
maltose into glucose and zymase enzyme non-human insulin causes allergic reactions in many
degrades, glucose into ethyl alcohol. diabetics. Recombinant DNA technology provided a
(b) By Fermentation of Sugary Foods: In this process way for scientists to produce human insulin in the
raw material is thick juice of sugarcane or syrup, laboratory.
Now, yeast is added in minute quantity in this The gene for human insulin is isolated from human
solution and is placed at 20-30°C after filling in cells and inserted into plasmids. These plasmids are
tanks. In this state, yeast produces two enzymes then introduced into bacterial cells, which manufacture
invertase and sucrase. These enzymes convert the insulin protein based on the human code. The
sugarcane syrup in glucose and fructose. Zymase purified product is identical in nature to human insulin
another enzyme produced by yeast, converts and does not cause any allergies.
glucose and fructose into ethyl alcohol. In addition to bacteria, other biotechnologists use yeast
(iii) Biotechnology, antibody and medicines: in recombinant DNA technology to make human
Achievements in the field of medicines are as insulin. Yeast can perform more of the complicated
follows: cellular processes that occur in human cells, making it
Molecular Diagnosis: Monoclonal antibodies are a more useful organism for producing human
used for the diagnosis of many diseases. substances.
This is produced by hybridoma technique. Jeorge Q.4. What are transgenic animals, why they are produced?
Kohler and Cosar Milstein were awarded by Explain in brief the usefulness of transgenic animals
Nobel Prize for preparing monoclonal antibodies. for human being. (2019, 20)
Inserting a particular antigen in the body through Ans. Animals that have their DNA manipulated to possess
vaccine, results in production of antibodies and express an extra (foreign) gene are known as
against that antigen. These are formed by plasma transgenic animals, e. g., transgenic rats, rabbits, pigs,
cells derived from B- cells. However, antibodies sheep, cows, mice and fishes. There are several
vary in physical and chemical forms due to benefits of transgenic animals.
variations in plasma cells. Now scientists isolated (i) Normal Physiology and Development :
one B-cell and fused it with that absurd cell which Transgenic animals can be specifically designed
has capacity of endless division. Now the cell to allow the study of regulation of gene and
formed by this, is called hybridoma cell. normal functioning of the body and its
These cells become source of pure antibody in a development. For example, the study of complex
long period, which are called monoclonal factors involved in growth such as insulin like
antibodies. Such antibodies work against only a growth factors.
single antigen. (ii) Study of Disease : Many transgenic animals are
Effects of chemotherapy and radiotherapy can be designed to increase the understanding about
presented by this. genes for contributing in the treatment of various
Gene Therapy: In this technique normal genes are diseases such as cancer, cystic fibrosis,
transferred in a person or an embryo to treat cells rheumatoid arthritis and Alzheimer.
with genetic disorders, which compensate (iii) Biological Products : Human diseases can be
inactive gene and accomplish its work. treated by medicines that contain biological
products.
112

(a) Transgenic animals that produce useful and was nutritionally a more balanced product
biological products can be created by the for human babies than natural cow’s milk.
introduction of the portion of the DNA or (iv) Vaccine Safety : Transgenic mice are being used
genes that code for a particular product such testing the safety of vaccines before they are used
as human protein (a-1-antitrypsin) which is on human, e. g., polio vaccine. If found reliable
used to treat emphysema. and successful they could replace the use of
(b) Similar attempts are being made for the monkeys in order to test the safety of batches of
treatment of Phenylketonuria (PKU) and the vaccine.
cystic fibrosis. For example, the first (v) Chemical Safety Testing : It is also known as
transgenic cow Rosie produced human toxicity or safety testing. It is similar to the
protein enriched milk (2.4 g/L) in 1997. The procedure used for testing toxicity of drugs.
milk contained the human alpha lactalbumin

NCERT Fully Solved Exercise

Q.1. Crystals of Bt toxin produced by some bacteria do not process of pollination by honey bees would be
kill the bacteria themselves because — affected.
(a) Bacteria are resistant to the toxin GM crops may also affect human health. Their
(b) Toxin is immature; (c) Toxin is inactive; products may be allergic to the body.
(d) Bacteria encloses toxin in a special sac. They can also cause genetic pollution in the wild
Ans. (c) Toxin is inactive. relatives of the crop plants. Hence, it can affect our
Q.2. What are transgenic bacteria? Illustrate using any one natural environment.
example. Q.4. What are Cry proteins? Name an organism that produce
Ans. Those bacteria in which foreign gene has been inserted, it. How has man exploited this protein to his benefit?
are called transgenic bacteria. Bacillus thuringiensis Ans. Certain bacteria produce special toxic proteins. These
and Agrobacterium are some of the important are called cry protein. These are toxic to insect larvae.
examples, in which desirable foreign genes have been Bacillus thuringiensis is one such bacterium. Its cry
inserted. Such bacteria can also be used as a vector for protein is also called Bt toxin protein.
further transferring foreign genes into crop plants. Our scientists have introduced its genes into the crop
Q.3. Compare and contrast the advantages and disadva- plants (Cotton etc.). This has enabled the crop plants
ntages of production of genetically modified crops. resistant to larval attack.
Ans. The production of genetically modified (GM) crops Q.5. What is gene therapy? Illustrate using the example of
has several advantages. adenosine deaminase (ADA) deficiency. (2020)
(i) GM crops are mainly developed for pest Ans. Gene therapy is a technique for correcting or replacing
resistance, which increases the crop productivity a defective gene with the healthy gene. It involves the
and reduces the dependence on chemical delivery of a normal gene into the individual to replace
pesticides. the defective gene.
Bacterium carrying
(ii) GM food crops also have enhanced nutritional plasmid with cloned Genetically Disabled
quality. So, these are good for health. normal humanADA gene Retrovirus

(iii) These plants prevent the loss of fertility of soil by

increasing the efficiency of mineral usage.
(iv) They are highly tolerant to changing
environmental conditions. Cloned ADA gene is
T-cells with Disabled incorporated into virus
(v) GM crops also decrease the post harvesting losses ADA gene isolated
from SCID patient Genetically altered
of crops. cells are reimplanted,
produce ADA
However, there are certain disadvantages of the use of
genetically modified crops. Retrovirus infects
The use of these crops can affect the native biodiversity T-cells, transfers
ADA gene to cells Cells are
in an area. For example, the use of Bt toxin to decrease grown in culture to
the amount of pesticide is posing a threat for beneficial ensure ADA gene is active

insect pollinators such as honey bee. If the gene

expressed for Bt toxin gets expressed in the pollen, For example : The adenosine deaminase enzyme is
then the honey bee might be affected. As a result, the important for the normal functioning of the immune
 113

system. The individual suffering from this disorder can naturally produces b-carotene (a precursor of vitamin
be cured by transplantation of bone marrow cells. A) pigment in its leaves.
The first step involves the extraction of lymphocytes Q.8. Does our blood have proteases and nucleases ?
from the patient’s bone marrow. Then, a functional Ans. No, human blood does not include the enzymes,
gene for ADA is introduced into lymphocytes with the nucleases and proteases.
help of retrovirus. Q.9. Consult internet and find out how to make orally active
These treated lymphocytes containing ADA gene are protein pharmaceutical. What is the major problem to
then introduced into the patient’s bone marrow. Thus, be encountered ?
the gene gets activated producing functional T- Ans. Orally active protein pharmaceuticals contain
lymphocytes and activates the patient’s immune biologically active materials such as peptides or
system. proteins, antibodies, and polymeric beads. It is
Q.6. Can you suggest a method to remove oil (hydrocarbon) administrated orally into the body in the form of
from seeds based on your understanding of rDNA capsules. These ingredients are used for treatment of
technology and chemistry of oil ? various diseases and are also used as vaccines.
Ans. Using rDNA, we can obtain oil less seeds by However, the oral administration of these drugs has
preventing the synthesis of either glycerol or fatty certain problems. One major problem is that, these
acids. This is done by removing the specific gene ingredients get digested by gastric pepsin and lipases in
responsible for the synthesis. the intestine. Hence, it is necessary to protect these
Q.7. Find out from internet what is golden rice? therapeutic protein from digestive enzymes, if taken
Ans. Golden rice is a genetically modified variety of rice, orally.
Oryza sativa, which has been developed as a fortified
food which is rich in vitamin A content. The plant

ccc
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Chapter

13
Unit-5 : Ecology

ORGANISMS
AND POPULATIONS

² Environment: The environment refers to the whole range of external conditions, physical and biological in which an organism lives.
It is the sum total of all biotic (living) and abiotic (non-living) factors that surround and potentially influence an organism.
² Species: Species is a group of similar individuals, which are capable of interbreeding and are able to produce fertile offspring.
Members of a species share a common gene pool.
² Biotic community: All kinds of living organisms living in a particular area at a particular time, form a biotic community. A
community contains individual of more than one species.
² Ecosystem: A well-defined area, containing both biotic and abiotic components is called an ecosystem. It is the basic functional unit of
ecology.
² Biome: A biome is a very large regional ecological unit, which is characterised by a major vegetation type and characteristic fauna,
found in a specific climatic zone.
² Photoperiodism: In plants, the duration of light has specific effect on flowering and other processes. This effect is called
photoperiodism.
² Climate: Climate refers to the average weather conditions of a particular area over a long time period. The climate reflects the general
patterns of atmospheric conditions, seasonal variations of a particular area.
² Microclimate: The climate of a very small local area is called microclimate. For example the immediate surroundings of plants and
animals in a garden or in a micro-ecosystem is an example of microclimate.
² Habitat: The place where an organism lives is called its habitat. Habitat of an organism is the best place, where it finds maximum food
and shelter.
² Niche: Niche (or ecological niche) is the positional status of an organism in an ecosystem. The niche of an organism determines (i) the
range of conditions, it can tolerate, (ii) the resources which it can utilise and (iii) the role it plays in the ecosystem.
² Cold-blooded animal (Poikilotherms): Animals, which do not have a constant body temperature and body temperature
fluctuates with the temperature of the surroundings are called cold blooded animals, e. g. , frog, fishes, reptiles etc.
² Warm-blooded animal (Homeotherms): Animals, which have a constant body temperature and body temperature does not
fluctuate with the temperature of the surroundings are called warm blooded animals, e. g. , birds, mammals.
² Soil Profile: A soil is formed by many horizontal layers, which are deposited one over the other. These can be seen in a vertical section
of soil. Such a vertical section, which shows the arrangement of various layers of soil is called soil profile.
² Producers: Producers are the organisms, which carry out photosynthesis and produce food from sunlight, e. g. , algae and green
plants.
² Consumers: Consumers are the organisms, which feed and depend on other organisms. Consumers mainly intake their food by
ingestive methods.
² Decomposers (reducers): These are the organisms, which feed upon the dead bodies and decaying organic matter of other
organisms (herbivores and consumers). These organisms decompose complex organic matter into simpler inorganic compounds, e. g. ,
bacteria and fungi.
² Acclimatisation: When an organism experiences some stress (within the tolerance range) it tries to avoid it, usually by migrating to
some other place or habitat. Such a mechanism to avoid environmental stress is called acclimatisation.
² Ecotypes: When a small group of a species lives in different climatic conditions over a long period of times, it becomes adapted to it.
Such locally adapted group (population) of a species is called ecotype.
² Adaptations: The adjustment of internal or self-environment by an organism, according to its external environment is called
adaptation. It is a fundamental property of all living beings.
 115

² Migrations: The movement of an animal or species from its native place to some other place in the search of food and shelter is called
migration.
² Mimicry: When an organism makes itself similar to another organism, the phenomenon is called mimicry. The organism, which is
making the changes, is called mimic, while other organism (which is being copied) is called model.
² Population: A group of individuals of same species which occupy a given area at a given time is called a population. The size of the
population usually depends upon the dimensions of the concerned area.
² Metapopulation: Metapopulation refers to a set of local populations that are connected by dispersing individuals.
² Population density: Population density refers to the total number of individuals present per unit area or volume at a given time.
² Carrying capacity: Food and space in a given area are limited. Therefore a given environment can support only certain number of
individuals. The maximum number of individuals of a population, that can be supported by a given habitat (environment), is called its
carrying capacity.
² Natality: It is also called birth rate. It is the increase in the number of individuals in a given population, by birth at a given time.
² Mortality: It is also called death rate. It is the number of individuals removed from a population due to death, under given
environmental conditions, at a given time.
² Biotic Potential: Biotic potential refers to the inherent maximum capacity of an organism to reproduce and increase in number.
² Dispersal: The movement of individuals into a population (immigration) or out of the population (emigration) is called dispersal. It
directly affects the size of a given population.
² Environmental Resistance: All those environmental factors, which put a check on the growth of the population, are together
known as ‘environmental resistance’.
² Mutualism: It is a functional interspecific association between two different species, in which both the species are benefited.
² Symbiosis: It is the condition/phenomenon in which there is a close physical association between the individuals of two different
species. The association is not harmful for any of the partners.
² Commensalism: It is an association between individuals of two different species, in which, one species is benefited and the other one
is neither benefited nor is adversely affected.
² Predation: It is a type of interaction between individuals of two different species, which involves the killing and consumption of one
(prey) by the other (predator).
² Competition: It is a type of interaction between two individuals, either of the same species or of different species, where both are
adversely affected.
² Parasitism: It is a type of interaction between individuals of two different species, where one (parasite) depends on the other (host)
for food and shelter and in the process, damages the host.
² Physiognomy: Various biotic and abiotic factors of a community decides the nature of the community and give it a characteristic look.
This look or outer appearance of a community is called ‘physiognomy’.
² Keystone species or ecological dominants: The species in a community, which have major influence on the nature of the
community, are called keystone species or ecological dominant.
² Ecotone: The transition zone between two adjacent communities is known as ecotone. Ecotone is therefore a common border for two
nearby communities.
² Edge effect: The ecotone (the border between two communities) has a greater biodiversity then either of the communities. This effect
is called edge effect.
² Ecological succession: Ecological succession is a community-controlled phenomenon where different communities are successively
replaced one after the other in a given area, till a climax community stage is reached, in an area, over a period of time.

Multiple Choice Questions 1 Mark

Q.1. The term ecology was coined by: Q.4. Epiphytes are considered as:
(a) Robert brown (b) Elton (a) Space parasites
(c) Haeckel (d) Reiter (b) Commensals of plant kingdom
Q.2. Root cap is absent in: (c) Obligate parasite
(a) Lithophytes (b) Xerophytes (d) (a) and (b) both
(c) Hydrophytes (d) Mesophytes Q.5. Vivipary and pneumatophore formation is seen in:
Q.3. Which type of water is used by the plant? (a) Apline forests (b) Arctic vegetation
(a) Gravitational water (b) Capillary water (c) Mangrove forests (d) Tropical forests
(c) Hygroscopic water (d) Bound water
 116

Q.6. Mycorrhiza shows: (a) Ruscus (b) Asparagus

(a) Symbiotic relationship (b) Endoparasitism (c) Opuntia (d) Accasia
(c) Decomposers (d) Ectoparasitism Q.11. Assimilatory root found in :
Q.7. Killing and eating an organism is: (a) Trapa (b) Ranunculus
(a) Parasitism (b) Exploitation (c) Typha (d) Lemna
(c) Predation (d) Symbiosis Q.12. The size of particles of clay soil is : (2018)
Q.8. Lichens represent : (a) 0.20-2.0 mm (b) 0.02-2.0 mm
(a) Mutualism (b) Commensalism (c) 0.002-0.02 mm (d) less than 0.002 mm
(c) Ammensalism (d) Parasitism Q.13. The interaction where one species is benefitted and the
Q.9. Which is one of the following rootless plant? other is neither benefitted nor harmed is called : (2019)
(a) Wolfia (b) Ranunculus (a) Ammensalism (b) Commensalism
(c) Ceratophyllum (d) All of these (c) Mutualism (d) Competition
Q.10. Cladode are found in : (2018)

Answers
1. (d) 2. (c) 3. (b) 4. (d) 5. (c) 6. (a) 7. (c) 8. (a) 9. (a) 10. (b)

11. (a) 12. (d) 13. (b)

Very Short Answer Type Questions 1 Mark

Q. 1. Define parasitism. (2017) Q. 9. In which plants vivipary germination is found?
Ans. Parasitism is an interaction between two species in (2015, 16)
which one species is benefited while the other species Ans. In mangrove plants — e. g., Rhizophora
is harmed. Q.10. What is “Gause’s competitive exclusion principle”.
Q. 2. Who used the term ecology? Ans. Gause’s principle state that two closely related species.
Ans. Reiter was the first, who proposed the term ecology in Competing for the same resources cannot co-exist
1868. indefinitely and the competitively inferior one will be
Q. 3. Define ecology? elimination eventually.
Ans. According to Ernst Haeckel. The study of reciprocal Q.11. What are you understand to urithermal and
relations between organisms and the environment is stanothermal organism?
called ecology. Ans. The species which can tolerate high range of
Q. 4. What is population ecology? temperature change, is called urithermal organism.
Ans. It lead with the growth, tropic structure, metabolism While the species which can tolerate low range of
and regulation of a population and interrelationship of temperature change is called stanothermal.
different populations and environment. Q.12. What do you mean by symbiosis? (2017)
Q. 5. What is habitat? Ans. Symbiosis is an interaction between two different
Ans. A living place of an organism is called habitat. organisms living in close physical association,
Q. 6. Who gave the term Ecological niche? typically of the same habitate, e. g., mutualism,
Ans. The term Ecological niche was first used by Grinnel in commonsalism etc.
1917. Q.13. The thorn is the modification of which plant’s part in
Q. 7. Air chamber/spaces are more developed in hydrophytic xerophytic plants?
plants. Give reason. Ans. Leaves
Ans. Air chambers help in floating of the plants in water. Q.14. Why are leaves of Opuntia modified into thorns? (2019)
They also help in the exchange of gases. Ans. Leaves of Opuntia are modified into thorns to reduce
Q. 8. Mesophytic plants die on placing in saline water. Give the rate of transpiration.
reason. Q.15. Write the names of any two ectothermic animals.
Ans. On placing in saline water or using high amount of (2019)
fertilizers. Water comes out of these plants through Ans. Reptiles and fishes are ectothermic animals. Body
plasmolysis and after sometime plants die. temperature of these animals depends on external
sources.
 117

Short Answer Type Questions 2 & 3 Marks

Q.1. What is ecological niche? How it is differ from habitat? Q.4. What is the importance of water in the life of plants?
Ans. Ecological niche indicated the profession of the Ans. (i) Water is the major component of the protoplasm.
species. It is the functional position of an organism in a (ii) Water is a solvent through which mineral
community. It is thus defining the specific position of nutrients enter in a plant from the soil solution.
the species in a habitat. It include habitat as well as (iii) Mineral nutrients absorbed by the roots and food
functional role of an organism in the community. The formed in leaves are transported by water.
concept of niche includes food relationship, prey (iv) All seeds require water for germination.
predator relationship tolerance capacity etc. (v) In photosynthesis O 2 is evolved by the photolysis
Q.2. What is mean by environment factors? Write its types? of water.
Ans. Each and every thing outside the organism which (vi) The high specific heat of water help plants to
influences in any way directly or indirectly the life of maintain relatively stable internal temperature.
the organism are called environment factors. (vii) It maintains turgidity of plant parts.
Ecological factors are classified as follows. (viii) It help in dispersal of seeds and fruits.
(i) Climatic factors: Light, temperature, wind Q.5. Write short note on:
velocity, gases, rainfall, atmospheric humidity. (i) Wilting (ii) Mangrove plants
(ii) Edaphic factors: Mineral matter, organic matter, Ans. (i) Wilting: When the transpiration rate is more than
soil water, soil air. the rate of water absorption from the soil plant
(iii) Topographic factors: Altitude, sleepness of leaves loss their turgidity and this condition is
slope, direction of slope. called wilting. In night transpiration rate becomes
(iv) Biotic factors: Bacteria, algae, fungi, parasites, slow and the leaves regain their natural turgidity.
saprophytes, symbionts and animals. This is known as temporary wilting. Under the
Q.3. What is the soil profile? Explain in brief. conditions of soil water stress, the wilted leaves
Ans. At any place where parent do not regain their natural state at night and
material is weathering over a remain as such then the wilting is called
period of time, there permanent.
develops layers of soil one (ii) Mangrove plants / Halophytes /
over the other in progressive Horizon-A Pneumatophores or Vivipary: Plants adopted
state of maturity. Such a for saline environment are halophytes. They occur
vertical section of soil is in salt lakes and in marine environment.
known as soil profile. The Horizon-B Mangroves which form shallow littoral forests
soil profile is characteristic near sea shores are halophytes. They grow in 3%
of fully formed soil and are level of NaCl salinity and thus they are
named as A, B, and C euhalophytes.
horizons from the surface to Horizon-C
These plants develop shallow rooting due to
downwards. water-logged environment where oxygen scarcity
(i) Horizon A: This is the prevails. To ensure proper aeration in root system,
topmost soil and it plants produce respiratory roots or
contains Rocks
pneumatophores, which are negatively geotropic
undecomposed, peg like projection above ground with pores for
partially decomposed Soil Profile gaseous exchange. The seeds of these plants
humus from upper to germinate before dehiscence of fruits or before
lower sides. This is usually sandy and the roots of break off from the mother plant. It is called
plants are embedded in this zone. This forms viviparous germination and phenomenon is
feeling zone. vivipary, e. g., Avicennia officinalis, Sonneratia
(ii) Horizon B: This is known as subsoil and is alba and Suaeda macrocarpa.
formed with clayey soils. Root develop poorly in Q.6. What do you understand by key-stone species?
this zones. Ans. Ecotone species are the transition zone present
(iii) Horizon C: It is the bottom of soil profile. It between two different types of communities. These
contains weathered rock of parent material. species convert the entire environmental condition of
Below this hard rocks are found.
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this area. i. e., convert green lands to deserts, e. g., Kind of Commensalism is a Parasitism is a
Kangaroo rats present in chihuahuan converted green interaction positive interaction. negative
interaction.
grasslands to the deserts.
Q.7. Describe the commensalism and mutualism. (2019) Benefits Here, only one In this
species gets benefits, relationship, only
Ans. Please see the ans of Long answer type question-1. while the other has one species get the
Q.8. An orchid plant is growing on the branch of mango no effects. benefits, while
tree. How would you describe the interaction between other is harmed.
two? (2019) Example 1. Barnacles growing 1. Salps and
Ans. Please see the ans of NCERT exercise question-8. on whales. Phronima.
Q.9. If a marine fish is placed in a fresh water aquarium, will 2. Climbers taking 2. Cuscuta and the
the support of trees to host plant.
the fish be able to survive? (2019) grow.
Ans. Please see the ans of NCERT exercise question-2.
Q.10. Write short notes on the following : (2019) Q.15. What is Mycorrhiza? Describe its ufility. (2020)
(i) Parasitism (ii) Symbiosis Ans. Mycorrhizae is a mutually beneficial relationship
Or What is symbiosis? Explain with the help of between the root of a plant and a fungus that colonizes
examples. (2019) the plant root. In many plants, mycorrhiza are fungi
Ans. (i) Parasitism : Please see the ans of Long answer that grow inside the plant’s roots, or on the surfaces of
type question-1. the roots.
(ii) Symbiosis : An interaction between two different Not all plants will have mycorrhizal associations. In
organisms living in same habitat in close physical environments in which water and nutrients are
association is known as symbiosis. It can be abundant in the soil, plants do not require the assistance
classified as following: of mycorrhizal fungi, nor might mycorrhizal fungi
o Commensalism : When one is benefitted and germinate and grow in such environments.
other is neither harmed nor benefitted, e. g., There are two predominant types of mycorrhizae:
orchid growth on mango tree. ectomycrrhizae and endomycorrhizae. They are
o Mutualism: When both the species are classified by where the fungi colonize on the plants.
benefitted, e. g., Lichens. (i) Ectomycorrhiza : Ectomycorrhiza tend to form
o Amensalism: When one is harmed and other mutual symbiotic relationships with woody
is neither benefitted nor harmed, e. g., plants, including birch, beech, willow, pine, oak,
Penicillium kills bacteria but not mould. spruce and fir. Ectomycorrhizal relationships are
Q.11. Explain the special morphological adaptations in characterized by an intercellular surface known as
xerophytes. (2019) the Hartig Net. The Hartig Net consists of highly
Ans. Please see Long answer type question-2. branched hyphae connecting the epidermal and
Q.12. Write a short note on predation. (2019) cortical root cells. In other words, ectomycorrhiza
Ans. Predatation : Please see Long answer type question-1. live only on the outside of the root. Overall, only
Q.13. What do you mean by hydrophytes? Describe 5-10% of terrestrial plant species have
hydrophytic adaptations in such plants. (2019) ectomycorrhiza.
Ans. Please see Long answer type question-3. (ii) Endomycorrhiza : Endomycorrhizae are found
Q.14. Explain the differences between parasitism and in over 80% of extant plant species-including
commensalism. (2020) crops and greenhouse plants such as most
Ans. vegetables, grasses, flowers and fruit trees.
Basis for Endomycorrhizal relationships are characterized
Commensalism Parasitism by the fungi and the formation of arbuscules and
comparison
Meaning Commensalism is the Parasitism is the vesicles by the fungi. In other words,
relationship where relationship endomycorrhiza have an exchange mechanism on
one organism of the where only one the inside of the root with the fungi’s hyphae
two different species organism receive
gains benefits while benefits, while the
extending outside of the root. It is a more invasive
other is unaffected. other is harmed in relationship compared to that of the
return. ectomycorrhiza.
Kind of Nonobligatory. They can be Utility of mycorrhiza : The plant and the fungus have
relationship Obligatory or a mutually beneficial relationship, where the fungus
Facultative. facilitates water and nutrient uptake in the plant, and
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the plant provides food and nutrients created by Ans. Please see the answer of question-15 of NCERT
photosynthesis to the fungus. This exchange is a exercise.
significant factor in nutrient cycles and the ecology, Q.20. Write down a short note on Allen’s rule. (2020)
evolution, and physiology of plants. Ans. Allen’s rule is an ecogeographical rule formulated by
In some cases, the relationship is not mutually Joel Asaph Allen in 1877, broadly stating that animals
beneficial. Sometimes, the fungus is mildly harmful to adapted to cold climates have shorter limbs and bodily
the plant, and at other times, the plant feeds from the appendages than animals adapted to warm climates.
fungus. More specifically, it states that the body surface
Q.16. Define commonsalism and give one example of it. area-to-volume ratio for homeothermic animals varies
(2020) with the average temperature of the habitat to which
Ans. Please see the answer of Long answer question-1. they are adapted (i. e., the ratio is low in cold climates
Q.17. Describe in brief the morphological adaptation in and high in hot climates).
hydrophyte. (2020) Allen’s rule predicts that endothermic animals with the
Ans. Please see the answer of Long answer question-3. same body volume should have different surface areas
Q.18. Write down the short note on interspecific competition. that will either aid or impede their heat dissipation.
(2020) Because animals living in cold climates need to
Ans. Interspecific competition : This competition occurs conserve as much heat as possible, Allen’s rule
between the individuals of two different species. Plants predicts that they should have evolved comparatively
and animals live together in the ecosystem. Process of low surface area-to-volume ratios to minimize the
competition between different species of plants and surface area by which they dissipate heat, allowing
animals is expressed in many types like competition for them to retain more heat. For animals living in
habitat, nutrition, water, light, etc., is commonly found warmclimates, Allen’s rule predicts the opposite: that
in different species of community. they should have comparatively high ratios of surface
For example, in Parthenium, plant secretes phenolic area to volume. Because animals with low surface
chemicals, due to which germination of nearby seeds area-to-volume ratios would overheat quickly, animals
stops. in warm climates should, according to the rule, have
Q.19. Define the following words and give one example of high surface area-to-volume ratios to maximize the
each. (2020) surface area through which they dissipate heat.
(i) Parasitism (ii) Mutulism

Long Answer Type Questions 5 Marks

Q.1. What is community interaction? Give its types with (i) Algae and Fungi (Lichens)
examples. (ii) Algae and higher plants
Ans. Community interactions: In a biotic community, the (iii) Bacteria and leguminous plants.
community of plants, animals and microorganisms (iv) Fungi and higher plants (Micorrhizal
interact with one another for sharing energy, resources associates)
and space. This is called community interactions. All (b) Commensalism: In this relation only one
these organisms are equally important for maintaining partner is benefited but other partner neither
ecological balance of earth and for proper functioning is harmed nor benefitted. This relationship
of the ecosystem. may be either permanent or temporary. e. g.,
Common type of interactions: (i) Epiphytic plants are considered as
1. Positive interactions commensals of plant kingdom. Lichens
2. Negative interactions and orchids are the classical example of
1. Positive Interaction: Such type of interactions in epiphytes.
which either one or both partners get benefited (ii) Epizoans are also commensals.
without harming. It is of following types. Cladophora grow on shells of snails.
(a) Mutualism: It is a type of permanent Some bacteria grow as commensal in the
association involving physiological intestine of man. (E.coli).
interdependance. In this both partners are
equally benefited, neither is harmed. e. g.,
120

(c) Protocooperation: It is an interaction (ii) Physically dry habitat: In this habitats, lack of
between two or more species which is water holding capacity in the soil; Like desert and
favourable but not obligatory to both. rocks.
e. g., Rhizosphere microflora. Some microo- (iii) Physically and physiologically dry habitats:
rganism grow in very closed association to Plants of some habitats are not able to utilize
roots of higher plants. Root secretes food for water and soil has less water holding capacity, due
microflora (fungi, bacteria) and microflora to which these habitat are physically and
provide inorganic nutrition for plants. physiologically dry habitat, like vegetation on
Oxpecker feeding on the skin parasites of mountains.
Rhino or cattle egret feeding on lice and
Morphological adaptations in Xerophytic plants
ticks.
They contain following morphological adaptations.
2. Negative Interactions: The interaction in which
usually one partner harms the other for deriving (i) Adaptation in roots: Root system is more
benefits for their own survival. developed. They grow into more depth. e.g., roots
It is of following types: of Alfalfa can go upto 130 feet depth in the
(i) Competition: There remains a competition ground. Root hairs and root caps are more
between two or more individual for space, developed. Sometimes roots also store water, e.g.,
light, water and energy resources. Asparagus.
(ii) Antagonism: Total or partial inhibition of (ii) Adaptation in stems: Stem in most of the plants is
the growth of one organism by another either woody, dry, hard and covered with thick bark. In
by modifying its immediate environment or some plant, it takes the form of bulb, e.g., Agave.
by secretion of some inhibitory chemicals. Sometimes stem modified into leaf like, e.g.,
None of them derive any benefit from such Ruscus and Opuntia. This is called phylloclade;
interactions, e. g., Antibiotic secretion from Asparagus contain cladode.
penicillin inhibiting growth of other (iii) Adaptation in leaves: Leaves modify into spines
competitors. in Opuntia, petiole becomes green and flat and
(iii) Parasitism: This is the interaction between takes the form of Lamina and does photosynthesis
two organisms in which one is called as in Parkinsonia, this is called phyllode, leaf
parasite and other is host. Parasite develop surface smooth and shiny, which reflects the heat.
nutritional relationship with the host, which
Leafy spines
is called parasitism. e. g.,
Cuscuta — total stem parasite.
Phylloclade Floral buds
Refflesia and Orobanche—total root
Flower
parasite.
Santalum — Partial root parasite. Leaf
(iv) Predation: This is the direct nutritional Scaly stipule
relationship between two organisms. It
include herbivores and carnivores. The Phylloclade
organisms which are nutritionally dependent (A)
on living prey are called predators and such (B)
type of parasitism is called predation. Cladode
Q.2. What are xerophytes? Describe their morphological
and anatomical characters with examples. (2013)
Or Write the characters of xerophytic plants.
(2011, 14)
Or Describe various morphological adaptations of
xerophytic plants. (2009, 10, 11, 16, 17) Stem
Ans. Vegetation present in dry habitat is called xerophyte. Leafy
These types of habitat are physiologically dry. These spines Scaly
can be of following types: leaf

(i) Physiologically dry habitat: In these habitats (C)

plants are not able to utilize the water although Fig. (a) Phylloclade of Ruscus (b) Phylloclade of Opunita
(c) Cladode in Asparagus
sufficient water is present, i.e., Saline, alkaline or
cold place.
 121

Anatomical adaptation in xerophytic plants: (ii) Hypodermis is absent in the stems of submerged
Following anatomical adaptations are present in plants, e.g., in Hydrilla and Potamogeton,
xerophytes. mechanical tissues are not present but cortex is
(i) Epidermis: It is multilayered in Nerium leaf and developed.
thick layer of cuticle is present. Upper surface has (iii) Air-cavities are present, due to which plants are
covering of wax in Capparis. able to float on the water.
(ii) Hypodermis: It is found multilayered. Q.4. With the help of suitable diagram describe the logistic
(iii) Cortex: Less intercellular space between the cells. population growth. (2020)
(iv) Vascular tissue: Surrounded by multilayered Ans. Logistic (sigmoid) growth model : Since food and
bundle sheath. shelter on the earth is limited, so no population in
(v) Mechanical tissues: These are well developed. nature actually has unlimited access to natural
(vi) Mesophyll tissues: Leaves contain palisade and resources to permit exponential growth. As a result of
spongy parenchymatous tissue. this there is a competition (intraspecific as well as
(vii) Stomata: Few and sunken stomata e.g., Nerium, interspecific) for limited resources. The individuals
Casuarina etc. who win this competition have a chance to survive and
Q.3. Describe ecological adaptations in hydrophytes plants. reproduce. So, the growth pattern of the population
Ans. Hydrophytes : These are found in aquatic becomes changed.
K
environment, which are sub merged or floating.

Number of individuals
Following types of adaptions are present in these.
Morphological adaptation in hydrophytic plants
S-shaped
Following morphological adaptations are found in
hydrophytic plants:
(i) Adaptation in roots: Their roots are poorly
developed, because entire part of the plant absorb Time
water. Sometimes roots are absent, like - Wolffia, Fig. Logistic (Sigmoid) population growth
Ceratophyllum. o In this type of growth pattern the growth of the
Some adaptations are given below : population is slow (gradual) in the beginning (lag
(a) Roots only work as balancing in Lemma. phase), but becomes very rapid thereafter (log
(b) Roots hairs are absent. phase).
(c) Root cap is not present. o It now grows with an exponential rate (maximum
(d) Roots of Trapa are green, so it performs rate) to reach a maximum size. When population
photosynthesis. reached the maximum size the growth rate
(ii) Adaptation in stems: Stems are long, thin, soft and becomes constant (steady phase).
spongy in submerged plants. Stem floats o It fluctuates slightly around the maximum size.
horizontally in free-floating plants, e.g., Azolla, (This maximum size of a population is called its
Eichhornia. Pistia has stolon. carrying capacity).
Stem of rooted hydrophytes spread on the bottom o This type of growth is called Verhulst - Pearl
to forms rhizome and remains fixed in the mud; Logistic Growth (or simply logistic growth).
e.g., Pistia and Nelumbium. o This type of growth is found in majority of
(iii) Adaptation in Leaves: Leaves of submerged populations.
plants are thin and ribbon shaped; e.g., Vallisneria o If the growth is plotted on a graph paper, a sigmoid
and these are large, flat and complete in floating or S shaped curve is obtained.
plants. Petiole is swollen in Trapa and o The S shaped growth pattern can be represented by
Eichhornia. the following equation, which includes an
Anatomical adaptations in hydrophytic plants : expression for environmental resistance —
Following anatomical adaptations are found in dN éK - Nù
= r Nê
hydrophytic plants : dt ë K úû
(i) Cuticle is not present on the epidermis, but mucus Where,
layer is present on the epidermis of floating plants, dN/dt = Rate of change in the population size, during
i.e., Pistia. Stomata are not present in submerged time t.
plants. r = Biotic potential or intrinsic rate of natural increase
N = Population density at time t.
K = Carrying capacity
122

We know that the growth of most of the populations is Therefore, logistic growth model is more accurate and
finite (limited) and sooner or later becomes stable. reliable.

NCERT Fully Solved Exercise

Q.1 How is diapause different from hibernation ? (e) Population density — It is defined as the number
Ans. Some zooplanktons in lakes etc., during unfavourable of individuals of a population present per unit area
periods undergo resting phase. This is called diapause. at a given time.
Hibernation on the other hand is a phenomenon in Q.6 If a population growing exponentially double in size in
which the organism undergoes deep into the soil to 3 years, what is the intrinsic rate of increase (r) of the
prevent itself from excessive cold. population ?
Q.2 If a marine fish is placed in a fresh water aquarium, will Ans. For a population growing exponentially,
the fish be able to survive? Why or why not ?(2019, 20) N t = N 0 e rt
Ans. No. It would not survive. This is because marine fishes Where,
have no mechanism to remove out excess of water, as N t = Population density after time t
found in the freshwater fishes. So, when a marine fish N 0 = Population density at time zero
is placed in fresh water, it will accumulate large r = intrinsic rate of natural increase
amount of water (due to endosmosis) and will e = the base of natural logarithms (2.71828)
eventually die. From the above equation, we can calculate the intrinsic
Q.3 Define phenotypic adaptation. Give one example. rate of increase (r) of a population.
Ans. Phenotypic adaptation are the changes in the body of Now, as per the question,
an organism in response to genetic mutation or certain Present population density = x
environmental changes. These changes occur in an Then, Population density after two years = 2x
organism to cope with changing environmental t = 3 years
conditions, e. g., desert plants have thick cuticles and Substituting these values in the formula, we get:
sunken stomata on the surface of their leaves to prevent 2x = x e 3 r
transpiration.
2 = e 3r
Q.4 Most living organisms cannot survive at temperature
Applying log on both sides:
above 45°C. How are some microbes able to live in
log 2 = 3r log e
habitats with temperatures exceeding 100°C ?
r = 0.2311
Ans. Many Archaebacteria are thermophiles. These are the
So, the intrinsic rate of increase (r) of the said
ancient forms of bacteria, which are found in hot water
population is 0.2311.
springs and deep sea hydrothermal vents. They are able
Q.7 Name important defence mechanisms in plants against
to survive in high temperatures (90°C to even 100°C)
herbivory.
because they are adapted to such environmental
Ans. Some plants have evolved various mechanisms to
conditions. These organisms contain specialized
protect themselves against herbivory. These methods
thermo-resistant enzymes, which carry out metabolic
include morphological changes and production of
functions at high temperature.
certain chemicals which are avoided by herbivores.
Q.5 List the attributes that populations but not individuals
(1) Morphological mechanisms:
possess.
(a) Cactus leaves (Opuntia) are modified into
Ans. The attributes that populations but not individuals
sharp spines.
possess are — (b) Sharp thorns are present in Acacia.
(a) Birth rate (Natality) —It is the ratio of births to the (c) In some plants, the leaf margins are spiny and
population of an area. have sharp edges.
(b) Death rate (Mortality) — It is the ratio of deaths to (2) Chemical production:
the population of an area. (a) Calotropis plant produces certain toxins,
(c) Sex ratio — It is the number of males or females which can prove to be fatal if ingested by
per thousand individuals. herbivores.
(d) Age distribution — It is the percentage of (b) Chemicals like nicotine, caffeine, quinine,
individuals of different ages in a given etc. produced by plants as a part of
population. self-defense.
 123

Q.8 An orchid plant is growing on the branch of mango animals live in burrows which do not get too hot
tree. How do you describe this interaction between the or too cold and have more humid (damp) air
orchid and the mango tree ? (2019) inside. These animals stay in their burrows during
Ans. The orchid plant growing on the branch of mango tree the hot days and emerge at night to feed. Other
is an epiphyte. The relation between the two is an animals have bodies designed to save water.
example of ecto-commensalisms, where one species Scorpions and wolf spiders have a thick outer
gets benefited while the other remains unaffected. In covering which reduces moisture loss. These
the above interaction, the orchid is benefited as it gets animals have long loops of Henle (in kidneys) to
support but the mango tree remains unaffected. make urine concentrated, so that they excrete less
Q.9 What is the ecological principle behind the biological water. The kangaroo rat found in the deserts of
control method of managing with pest insects ? Arizona never drinks water in its life. It has the
Ans. The ecological principle behind the biological control ability to concentrate its urine to conserve water.
method of managing with pest insects is based on (b) Adaptations of plants to water scarcity: Plants
predation. Predation is a biological interaction between in desert are well adapted to cope with water
a predator and its prey. In this interaction, the predator scarcity. They have an extensive root system to
feeds on the prey and thereby, controls the prey tap underground water. Further, they bear thick
population. In biological control, various insects and cuticle on leaves, leaves are reduced to minimize
birds are used to feed upon insect pests. surface area and leaves have sunken stomata. All
Q.10 Distinguish between the following: these changes help the plant to reduce the rate of
(a) Hibernation and Aestivation transpiration. In Opuntia, the leaves are modified
(b) Ectotherms and Endotherms into spines and photosynthesis occurs in green
Ans. (a) Hibernation and Aestivation: Hibernation is a and fleshy stems. In many desert plants, a
state of reduced activity in cold blooded animals photosynthetic pathway is found, which is called
to escape cold winter conditions. Aestivation is a CAM (C4 pathway). It enables their stomata to
state of reduced activity in cold blooded animals remain closed during the day to reduce water loss
to escape extreme heat in summers. by transpiration.
(b) Ectotherms and Endotherms: Ectotherms are (c) Behavioural adaptations in animals: The
cold blooded animals. Their temperature behaviour of the animals is directly affected by
fluctuates with the changes in their surroundings, changes in climatic conditions particularly
e. g., Fishes, amphibians, and reptiles. temperature. Some animals can live only in a
On the other hand, endotherms are warm blooded small range of temperature, they are called
animals. They maintain a constant body stenothermal animals. On the other hand some
temperature, e. g., birds and mammals. other animals can survive effectively in a wider
Q.11 Write a short note on : temperature range. These are called eurythermal
(a) Adaptations of desert plants and animals animals.
(b) Adaptations of plants to water scarcity Certain organisms are affected by temperature
(c) Behavioural adaptations in animals variations. These organisms undergo adaptations
(d) Importance of light to plants such as hibernation, aestivation, migration, etc. to
(e) Effect of temperature or water scarcity and the escape environmental stress to suit their natural
adaptations of animals.
habitat. These animals are called ectotherms (or
Ans. (a) Adaptations of desert plants and animals:
poikilotherms). They are cold blooded animals
Plants found in deserts are well adapted to cope
such as fish, amphibians, reptiles, etc. For
with harsh desert conditions such as water
example — the desert lizard basks in the sun
scarcity and extreme heat. Plants have reduced
during early hours when the temperature is quite
leaves, thick cuticles and sunken stomata to check
low. However, as the temperature begins to rise,
transpiration. They have an extensive root system
the lizard burrows itself inside the sand to escape
to tap underground water. They bear thick cuticles
sunlight.
and sunken stomata on the surface of their leaves
Other animals, in which body temperature
to reduce transpiration. Desert plants have special
remains constant, are called endotherms or
pathways to synthesize food, called CAM (C4
homeotherms. They are warm-blooded animals,
pathway) where stomata open at night.
such as birds and mammals. They also escape cold
Desert animals prevent water loss from their
and hot weather conditions, by hiding themselves
bodies in a number of different ways. Some
124

in shelters such as caves, burrows, etc. to protect (c) Most organisms in the benthic zone are
against temperature variations. scavengers and detritivores. These include many
(d) Importance of light to plants: Plants are corals, sponges, crabs and polychaete worms.
autotrophic organisms, which need light for Q.14 Define population and community.
carrying out the process of photosynthesis. So, Ans. Population : A population can be defined as a group of
sunlight is the ultimate source of energy. Light individuals of the same species residing in a particular
also plays an important role in generating geographical area at a particular time and functioning
photoperiodic responses such as flowering, seed as a unit. For example — all human beings living at a
germination etc. Light also plays an important particular place at a particular time constitute human
role in aquatic habitats for vertical distribution of population.
plants in the sea. Community : A community is defined as a group of
(e) Effects of temperature or water scarcity and individuals of different species, living in a
the adaptations of animals. Animals are well geographical area. In a biotic community, various
adapted to suit surrounding temperature and water organisms of different species live together and
scarcity. They are able to hind themselves in caves establish interspecific interactions.
and burrows and other shady places to avoid Q.15 Define the following terms and give one example for
extreme heat. They have adaptations to cope with each :
water scarcity particularly in desert. They produce (a) Commensalism (b) Parasitism
concentrated urine, feed on succulent plants. (c) Camouflage (d) Mutualism
Some have thick cuticle on skin to prevent water (e) Interspecific competition
loss. Ans. (a) Commensalism: Commensalism is an interaction
Q.12 List the various abiotic environmental factors. between two species in which one species gets
Ans. Various abiotic environmental factors are given below: benefited while the other remains unaffected. For
(a) Light: Light is the primary source of energy. Light example: an orchid growing on the branches of a
helps in various phenomena like photosynthesis, mango tree.
photoperiodism, pigmentation, vision, growth etc. (b) Parasitism : It is an interaction between two
(b) Temperature: For proper functioning, all species in which one species (parasite) gets the
organisms require an optimum temperature. benefit, while the other species (host) is
Temperature directly influences the rate of negatively affected. For example: Ascaris, living
metabolic activities. Low temperature treatment is in human intestine.
necessary for flowering in many plants (c) Camouflage : It is a strategy adapted by prey
(vernalisation). species to escape their predators by changing their
(c) Water: Water is the habitat of all aquatic colour according to surroundings, so that they can
organisms. It is essential for photosynthesis. It is easily mingle in their surroundings and escape
the main source of oxygen (released in their predators.
photosynthesis). Water is essential for metabolic (d) Mutualism : It is an interaction between two
activities of organisms. Water helps the species in which both species are benefited. For
organisms to get rid of excessive heat. Water example: lichens show a mutual symbiotic
helps in the absorption of minerals by the plants relationship between fungi and algae.
from soil. (e) Interspecific competition: An interaction
(d) Soil: It is the upper shallow layer of earth, which between individuals of different species where
consists of very fine sand particles, organic and both species are negatively affected. For example:
inorganic depositions. It forms the habitat of all the competition between flamingoes and resident
terrestrial organisms and microorganisms. It helps fishes in South American lakes for common food
to anchor the plants. It provides water and mineral resources i. e., zooplankton.
ions to the plants. Q.16 With the help of suitable diagram describe the logistic
Q.13 Give an example for : population growth curve. (2020)
(a) An endothermic animal Ans. Please see the answer of Long answer type question-4.
(b) An ectothermic animal
Q.17 Select the statement which explains best parasitism.
(c) An organism of benthic zone
(a) One organism is benefited.
Ans. (a) Birds and mammals (b) Both the organisms are benefited.
(b) Frog and lizards (c) One organism is benefited, other is not affected.
 125

(d) One organism is benefited, other is affected. (b) Death rate (mortality): It is the ratio of the
Ans. (d) One organism is benefited, other is affected. number of deaths to the population of an area in a
Parasitism is an interaction between two species specific time. A rise in the mortality decreases the
in which one species (parasite) is benefited while population size.
the other species (host) is harmed. (c) Age Distribution: It is the percentage of
Q.18 List any three important characteristics of a population individuals of different ages in a given
and explain. population. The age distribution pattern is
Ans. Three important characteristics of a population are: commonly represented through age pyramids. A
(a) Birth rate (natality): It is the ratio of the number rise in pre-reproductive age shows the expanding
of births to the population of an area in a specific nature of the population.
time. A rise in the natality increases the
population size.
ccc

Note : Due to Covid-19 Chapter-14 (Ecosystem) is not in the Latest Syllabus 2020-21.
 Chapter 14 : Ecosystem
126
(This Chapter has been Deleted From Syllabus For Session
2020-21 Due To COVID-19 Epidemic)
Chapter

15
BIODIVERSITY AND
ITS CONSERVATION

² Biodiversity: The term biodiversity refers to the totality of genes, species and ecosystems of a given region.
² Genetic diversity: Genetic diversity refers to the variation of genes within a species. Genetic diversity is the primary cause of
biodiversity.
² Species diversity: Species diversity refers to the variety of species within a region / ecosystem.
² Protected areas: These are the areas of land or sea, which are specially dedicated to the protection and maintenance of biological
diversity of natural and cultural resources.
² Biosphere reserves: Biosphere reserves are specialised protected areas of land or coastal environments, which provide shelter to the
wildlife in a natural way.
² Cryopreservation: Cryopreservation is the storage of materials at ultra-low temperatures either by very rapid cooling or by gradual
cooling and simultaneous dehydration at low temperatures.
² Hot spots: The hot spots are the designated priority areas, for in situ conservation of biodiversity. 25 hot spots have been recognised
world-wide, out of which 2 lie in India.
² Red list: It is a report, which is published by IUCN that contains the names and status of endangered species.
² Sixth Extinction: Study of fossils records show that, species extinction is not a new phenomenon. It has happened earlier also, even
before humans appeared on the earth. Since the origin and diversification of life on earth there were five episodes of mass extinction of
species.
Therefore the present rapid extinction of species can be regarded as ‘sixth extinction’.

Multiple Choice Questions 1 Mark

Q. 1. The concept of hot spots was given by: (c) Maharashtra (d) Punjab
(a) Spencer (b) Norman Myer Q. 7. Which National park is new home of the India one
(c) Haeckel (d) Odum horned rhinoceros?
Q. 2. Number of wild life sanctuaries in India is: (a) Kanha (b) Corbett
(a) 442 (b) 492 (c) Dudhwa (d) Bandhavgarh
(c) 339 (d) 428 Q. 8. Which of the following is not an Indian biodiversity
Q. 3. Which National park, was first established in India? hot-spot? (2018)
(a) Kaziranga (b) Gir (a) Indo-Burma
(c) Jim Corbett (d) Dudhwa (b) Eastern Himalayan
Q. 4. Which one is endangered species of India? (c) Western Ghats and Sri Lanka
(a) Horse (b) Fox (d) Medagaskar and Hind Mahasagar Island
(c) Indian wild Ass (d) Elephant Q. 9. The world biodiversity day is celebrated annually on:
Q. 5. Wild life protection act was passed in which years? (a) 5th June (b) 22nd April
(2014) (c) 29th December (d) 16th September
(a) 1986 (b) 1973 Q. 10. Which of the following is state bird of U.P.? (2018)
(c) 1991 (d) 1981 (a) Peacock (b) Crane
Q. 6. Kaziranga National park is situated in which state? (c) Pegion (d) Sparrow
(a) Assam (b) Gujarat Q. 11. Which is the National Animal of India? (2018)
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(a) Elephant (b) Deer (c) Gujarat (d) Madhya Pradesh

(c) Bear (d) Tiger Q.13. The most dangerous reason for the existence of lives is:
Q.12. Where is Situated ‘‘Gir National Park’’ the natural (2020)
habitat of Asia Lions? (2018) (a) Desertation (b) Radiation
(a) Uttarakhand (b) Rajasthan (c) Deforestation (d) None of these

Answers
1. (b) 2. (b) 3. (c) 4. (c) 5. (b) 6. (a) 7. (c) 8. (d) 9. (c) 10. (b)

11. (d) 12. (c) 13. (c)

Very Short Answer Type Questions 1 Mark

Q. 1. Name any two threatened animal species of India. Q. 8. Who is called as "The old man of the Jungle" ?
Ans. Red Panda and Black Buck. Ans. Orang -Utan is called as "The old man of the jungle"
Q. 2. What are the endangered species? (2019) Q. 9. What is wild life?
Ans. The species which are in danger of extinction and Ans. Wildlife include all wild animals, tree and plants which
whose number have been reduced to a critical level are inhabit their original natural habitats. Thus, they
called endangered species. cannot ordinarily be domesticated and trees and plants
Q. 3. What are hot spots? Give the name of two hot spot of which cannot ordinarily be cultivated.
India. (2014, 17, 18) Q. 10. What is ‘‘Red Data Book’’? Who prepared it? (2018)
Ans. The hot spots are the designated priority area, for in situ Ans. See Short Answer Type Q.No. 5
conservation of biodiversity. In India Eastern Q. 11. What is Sanctuaries? (2018)
Himalayas and Western Ghats are main hot sports. Ans. See Long Answer Type Q.No. 1 (ii)
Q. 4. Give the full form of the following: (2018) Q. 12. What are extinct species? (2018)
(i) IBWL (ii) IUCN Ans. When any plant or animal species are not present on the
Ans. (i) IBWL = Indian Board for Wildlife earth anywhere, i.e. they are died. Such species are
(ii) IUCN = International Union for Conservation of called extinct species. According to IUCN Red List,
Nature and Natural Resources. 784 species are extincted in last 500 years.
Q. 5. What is ex-situ conservation? Q. 13. When the environment (Protection) act was passed by
Ans. To protect the wildlife to outside from their natural Government of India? (2019)
habitat is termed as ex-situ conservation. Ans. In 1986.
Q. 6. What is full form of MABP? Q. 14. Define national park. (2019)
Ans. Man And Biosphere Programme. Ans. National park is an area strictly reserved for protection
Q. 7. Give two examples of National parks of India? and betterment of wildlife. We have 77 national parks
Ans. 1. Gir Forest: Kathiawar, Gujarat only home of in our country.
Asiatic lion in India?
2. Kaziranga: At banks of Brahmaputra river, near
manas tiger reserve in Assam.

Short Answer Type Questions 2 & 3 Marks

Q. 1. Explain the reasons of elimination of destruction of only way can acquire new land for these purposes
natural habitats of wild animals? is by eliminating forests.
Ans. The man of present era is grossly guilty of this in 2. Forests Fire: Since ancient time, forest fires
various ways as follows. caused due to human negligence, have brought
1. Acquirement of New Land for Increasing about large scale destruction of forests.
Human Population: As human population 3. Highway Conveyance and Transportation:
progressively increases, more and more new land Construction of roads and laying of railway lines
is required for expanding human habitations. The through the wilderness for long distance
conveyance and transportation play a significant
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role in fragmentation and shrinking of natural Tiger" the number of tigers increased from about 1800
habitats. in 1973-1974 to about 4000 in 1985.
4. Human Greed for Forest Proudest: Many areas Q. 5. Write short note on Red Data Book? (2018)
have been deforested and turned into dry, infertile Or What is Red Data Book? Give its significance.
lands due to human greed for forest product like (2014, 15)
timber, herbs, flowers etc. Ans. IUCN is international union for conservation of nature
Q. 2. Write the reasons of the animals being extinct? and natural resources, which is now called world
(2014, 16) conservation union (WCU). Its head quarter is situated
Ans. Artificial destruction of wild animals due to human at Morges, Switzerland. It maintain a Red Data Book or
activities has, caused extinction of a sizable number of red list which is a catalogue of threatened plants and
wild animal species. These human activities are mainly animals facing risk of extinction. The IUCN red list
as follows: system was started in 1963. Since then, evaluation of
1. To obtain skin and fur we have killed wild animals conservation status of species and subspecies is
and now they have become endangered. continuing on a global scale. The 2000 red list contains
2. Due to usage of elephant teeth they have killed. assessments of more than 1800 species. It can helpful
3. Millions of snakes have been killed for skin. in:
4. Due to migration of warm blooded wild animals (i) Identification and documentation of endangered
between the colder and hotter parts of India many species.
of these become threatened. (ii) Developing awareness about the importance of
5. Certain species of wild animals are widely used in threatened biodiversity.
education and research. (iii) Providing a global index of the decline of
All these causes many wild animals species to the biodiversity.
brink of extinction. Q. 6. Differentiate the National Park and Sanctuary.
Q. 3. Write short note on the in situ conservation. Ans. Differences between National Park and Sanctuary.
Ans. In situ conservation requires protection of wild animals National Park Sanctuary
in their natural habitats. These habitat are, therefore
declared as prohibited reserves. According to the 1. It is protected area for both It is a protected area for wild
degree of environment protection afforded. We have animals and plants. animals only.
four types of reserves in our country as follows— 2. Boundary is well Boundary is roughly
(1) National Parks: It is an area strictly reserved for demarkated. demarkated.
protection and betterment of wildlife. We have 77 3. Private ownership is not Private ownership is permitted.
national parks in our country. permitted.
(2) Sanctuaries: These are notified and controlled by 4. Plantation, cultivation and They are permitted.
state government for the protection of wild grazing are not permitted.
animals fauna. There are about 421 sanctuaries in
5. Collection of even minor Harvesting of timber and
our country. forest product is not collection of minor forest
(3) Tiger Reserves: Some of the national parks and allowed. products are permitted.
sanctuaries were declared as special ‘Tiger
reserves’. These reserves are controlled by state Q. 7. Why is it important to protect wild animals? What are
government but funded by both central and state the steps taken by government for this?
government. Ans. Wild animals came under the biotic factors of the
(4) Biospheres Reserves: Biosphere reserve is environment. These are different species of varied
visualized as a perfect natural ecosystems meant numbers, but a sudden change in population cause
to preserve, not only the wilderness, but also the imbalance in the environment.
full wildlife gene bank. To protect wild animals following steps have been
Q. 4. Write short note on the project Tiger? (2017) taken by the government
Ans. Fast decreasing causes of the royal Bengal Tiger (i) ZSI (Zoological Survey of India): Its main
prompted the Indian Government in 1972-73 to declare objective is to conserve the wildlife.
the tiger as National animals, and to launch a special (ii) Indian Board for Wildlife: This board was setup
‘Project Tiger’ to save this magnificant member of our for the conservation of wildlife. Its main work was
natural bounty from extinction. As a result of "Project to make national parks, wild sanctuaries and
zoos as well as to keep animals safe in them.
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(iii) In Indian constitution hunting is prohibited.

(iv) Cutting of forests was illegalized. Q.12. What do you mean by National park? Give the name of
(v) Planting of trees was made a continuous process first National Park of India. (2018)
at national level. Or Write a short note on national park. (2020)
(vi) The endangered species are observed by Indian Ans. See Long Answer Type Q.No. 1 (II)
wildlife protection department and its log is kept Q.13. What are Sanctuaries? How many sanctuaries are
in Red Data Book. situated in India? (2015, 17, 18)
Q. 8. Write a short note on Biosphere reserve. (2018, 20) Ans. See Long Answer Type Q.No. 1 (II)
Or What is Biosphere reserve? Write the name of two Q.14. What are endangered wild species? Describe in short.
protected Biosphere reserve of India? (2018) (2017, 18)
Ans. See Long Answer Type Q.No. 1 (II) Ans. Those species, which are of a verge of extinction and to
Q. 9. Define hotspot. Write the names of two hotspots in protect them is difficult, are called as endangered
India. (2017) species. There are 172 species in India which are listed
Or What are biodiversity hotspots? How many as threatened by IUCN, in which 53 are mammals, 69
hotspots are there in India? Write down their names. are birds and 23 are amphibians and 3 are rare animals.
(2018) Other than this, 22 invertebrate species also come
Ans. Those geographical areas where there is immense under this category. In India, there are many rare
biodiversity (wildlife and plants) and their natural species like Bengal fox, Asiatic cheetah, Asiatic lion,
homes are in danger, i.e. the natural resources are Indian elephant, Asiatic wild ass, Indian rhinoceros,
excessively exploited. These areas are known as Cervus elaphus hangul, thamin or brow antlered deer,
hotspots. There are 3 hotspots located in India. Presbytis geei, snow leopard-Panthera uncia, Gavial
In India, Eastern Himalayas, Western Ghats and gavialis, Ardeotis nigriceps and Gibbon-Hylobates,
Indo-Burma are major hotspots. etc.
Q. 10. Explain the ex-situ and in-situ conservation of wild Q.15. What is co-extinction? Give its one example. (2019)
animals in India? . (2018) Ans. Please see Long answer type question-1.
Ans. See Long Answer Type Q.No. 1 Q.16. Write a short note on biodiversity. (2019)
Q. 11. Give the name of four National Parks located in India. Ans. Biodiversity : Please see the answer of Long answer
(2018) type question-1.
Ans. Some National Parks of India : Q.17. Write a short note on WWF. (2020)
Ans. The world fund for nature (WWF) is an international
Name State Estab- Area (In Notability
lished km 2 ) non-governmental organization founded in 1961 that
works in the field of wilderness preservation and the
Dudhwa Uttar 1977 490.29 Tiger Panthera tigris, reduction of human impact on the environment. It was
National Pradesh Sambhar Axis axis, Hog formerly named the World wildlife fund, which
Park Deer Axis procinus.
remains its official name in Canada and United States.
Gir Forest Gujarat 1965 1412 Asiatic lion. Q.18. Write a short note on threatened species. (2020)
National
Park Ans. Threatened species are any species (including animals,
plants, fungi, etc.) which are vulnerable to
Indravati Chhattisgarh 1981 1258.37 Wild Asian buffalo, endangerment in the near future. Species that are
National tiger reserve, hill
Park mynas. threatened are sometimes characterised by the
population dynamics measure of critical depensation, a
Jim Uttarakhand 1936 1318.5 First national park in mathematical measure of biomass related to population
Corbett India (established in
National 1936 as Hailey growth rate.
Park National Park). Threatened Species Definition
A threatened species is any species which is
Kaziranga Assam 1974 858.98 Highest known tiger
National density in the World vulnerable, endangered, or critically endangered. The
Park Indian rhinoceros, International Union for Conservation of Nature, or
UNESCO World IUCN, is commonly referenced as a leading
Heritage Site. organization in determining if a species can be
Keoladeo Rajasthan 1981 28.73 UNESCO World considered a threatened species or not.
National Heritage Site.
Park
 130

Ans. Differences between ex situ and in situ conservation

Threatened Species Overview are given below
The IUCN also defines the category nearly-threatened In Situ Conservation Ex Situ Conservation
species, for any animals which are likely to become
threatened species within the foreseeable future. The It is conservation of It is conservation of
endangered species in endangered species outside
IUCN designation of threatened species can be seen their natural habitats. their natural habitats.
below.
Extinct Near
The endangered species The endangered species are
in wlld Threatened threatened are protected from protected from all adverse
predators. factors.
EX EW CR EN VU NT LC The depleting resources They are kept under human
Endangered are argmented. supervision and provided all
Extinct Critically Vulnerable Least the essentials.
endangered concerm
The population recovers Offsprings produced in
Q.19. Write a short note on Hotspots’. (2020) in natural environment, captive breeding are released
Ans. Those geographical areas where there is immense e. g ., hotspots, protected in natural habitat for
biodiversity (wildlife and plants) and their natural areas, etc. acclimatisation, e. g ., gene
homes exploited. These areas are known as hotspots. bank, cryopreservation, etc.
There are 3 hotspots located in India. Q.21. Write a short note on ‘‘Biodiversity’’. (2020)
In India, Eastern Himalayas, Western Ghats and Indo- Ans. See the answer of Long answer type question-1.
Burma are major hotspots.
Q.20. Difference between in situ conservation and Ex situ
conservation. (2020)
Long Answer Type Questions 5 Marks

Q. 1. What is biodiversity? How can we preserve it? Write country has 275 zoos, safari park and aquaria. In India
the reasons of its degradation? there are many zoological museums in which extinct
Or What is biodiversity? Write two procedures for its species are kept.
preservation? (a) Botanical gardens:These are the large,
Or What do you understand by biodiversity? What are artificially made natural surroundings where a
the causes of biodiversity loss? Explain two methods of large number of plant species are kept. Botanical
biodiversity conservation. (2019) gardens are significant for their plant diversity.
Or What do you mean by biodiversity? How it can be There are more than 1500 botanical gardens in the
preserved? (2020) world. Some important are described below —
Ans: Biodiversity: The term ‘biodiversity’ refers to the 1. Royal Botanical Garden Kew — It is the
totality of genes, species and ecosystems of a region. largest botanical garden of the world. It is
The biodiversity therefore includes different types of located at Kew (England) and was founded in
genes, different types of organisms, species and 1759 by Willium Aiton. It has about six
ecosystems. The distribution of organisms is not even. million specimens of plants.
It depends upon the habit and habitat of the organism. 2. Museum of Natural History — It is located in
Therefore biodiversity differs from place to place. Paris (France). It also contains about six
Taking into consideration, the total habitats of plants million specimens of plant species.
and animals, we can say that the living world abounds 3. New York Botanical Garden — It is located
in New York (USA) and was founded in
with enormous biodiversity.
1801. It contains about 4.5 million specimens
We can conserve biodiversity in the following ways.
of plants species.
Conservation of biodiversity 4. British Museum of natural history — It is
I. Ex situ conservation: To protect endangered species, located in London. It contains more than 4
they are kept out of their natural homes, Zoos, Games million plant specimens.
farms, Safari parks, Aquaria, Botanical gardens, Seed 5. Indian Botanical Garden — It is situated in
banks and Gene banks are the examples of ex situ Kolkata, India. It is the biggest botanical
conservation. Ex situ conservation has different garden of India. It contains about 1.5 million
solutions, where wildlife are conserved. In present our plant specimens.
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Significance of botanical garden engineers and plant and animal breeders to

♦ Botanical garden provides the visitor to compare quickly obtain the genetic material of their choice.
plants in their natural living conditions. (e) Establishing gene bank: Threatened,
♦ Botanical garden provides material for botanical endangered and desired genes of wildlife and
research. living beings are kept at a safe place which is
♦ Botanical garden provide on the spot education known as gene bank. In these institutions the
about the plants. plants are grown through seeds and are kept
♦ Botanical garden provides shelter to endangered safely. These are called as the storage for future
species. viable seeds.
♦ Botanical garden acts as a huge library of plants. (f) Cryo-preservation: In this the germplasm of
(b) Zoological parks: Zoological parks and gardens threatened and endangered species is kept at very
are the protected and enclosed areas, which are, low temperature (-196° C) in liquid nitrogen.
developed to provide shelter to wild animals. In this process the biological activities, mitosis
Main object of creating the zoological parks is to and genetic changes stop. It is known as
create among people an interest and curiosity for cryo-preservation.
animals. Various types of animals are kept in a II. In situ conservation: In this conservation, different
zoological park for their protection, exhibition species and genes are preserved in natural habitat. In
and study purposes. the year 1982, the Indian wildlife board was
Zoological parks are mainly run by the central and established. This board works and organizes different
state governments. However some programmes for the natural habitat, their care-taking,
non-government organisations (N.G.Os) are also etc. and the topics related to them.
active in this direction. To conserve biodiversity in its natural habitat, national
Zoological parks guard animals against their parks, sanctuaries and biosphere reserves are made.
natural enemies and also against starvation. They (a) National parks: They are areas reserved for
are also given medical treatment and facilities. wildlife where the latter is able to obtain all the
Some important zoological parks of India are — required natural resources and proper habitats.
1. Zoological Garden, Kolkata. Plantation, cultivation, grazing, felling of trees
2. Zoological Park, Itanagar, Arunachal and habitat manipulation are not allowed. Private
Pradesh. ownership is not permitted. At present India has
3. Zoological garden, Bikaner, Rajasthan. 112 National parks. The early national parks
4. Nehru Zoological Park, Hyderabad.
( e. g., Yellowstone Park in U.S.A., Royal Park
5. Nandan Kanan Zoological Park,
near Sydney, Australia) were chosen for their
Bhuvneshwar, Odisha.
scenic beauty and recreational values. They now
6. Prince of Wales Zoological Garden,
contain and protect rare species and wilderness
Lucknow.
7. National Zoological Park, Delhi. areas. Jim Corbett National Park near Nainital
8. Sephijala Zoological Park, Tripura. (Uttarakhand) was the first national park
9. Kamla Nehru Zoological Garden, established in India 1936. Keoladeo, Kaziranga
Ahemedabad. and Manas have been included among world
10. Indira Gandhi Zoological Park, heritage sites.
Vishakhapattanam. (b) Sanctuaries: They are tracts of land with or
(c) Storage of seeds, pollen and tissue cultures: without a lake where animals are protected from
The structures like seeds, pollen and tissue all types of exploitation and habitat disturbance.
cultures of important and endangered species can Private ownership is permitted. Collection of
be protected by storing them at a very low minor forest products, harvesting of timber and
temperature. The storage of materials at very low wood, tilling of land and other activities are
temperature (–196°C) is called cryopreservation. allowed provided they do not interfere with the
This temperature is usually achieved with the help welfare of animals. Presently India has 515
of liquid nitrogen. sanctuaries.
(d) Gene or DNA banks: The germplasm or genes (c) Biosphere Reserve:
(DNA) of important species can also be stored in ♦ Biosphere reserves are specialised protected areas,
gene or DNA banks. These banks help genetic which represents natural biomes and contain
unique biological communities.
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♦ The concept of Biosphere Reserves was given increased in last 150 years. Regular increase
in 1975 as a part of UNESCO’s ‘Man and in the residential areas, agricultural area,
Biosphere Programme’ (MAB). industrial areas has decreased the area of
Transition zone forest from 18% to very less. The Amazonian
rainforest has been cleared for soybean
Buffer zone
farming and pasteurization.
Core area Q. 2. Write an essay on wild animals in India. (2020)
Ans: Various types of wild animals are found in the forests
Human of India. Since primitive days the wild animals have
settlement close relationship with the mankind. The major wild
animals of India are elephant, tiger, lion, rhino, bear
Fig. Zonation in biosphere reserve
etc. They live in the dense forests.
Construction of a biosphere reserve : A Biosphere The Sundarban of West Bengal is the home of the
Reserve consists of the following zones — Royal Bengal Tigers. Similarly lions live in the Gir
(1) The core zone : It is the inner central part that Forest of Gujarat, and rhinoceroses live in the dense,
comprises an undisturbed and legally protected marshy and moist forests of Assam, north Bengal and
ecosystem. Tripura. Elephants and tigers live in the forests of
(2) The buffer zone : It lies in the middle and Orrissa, Madhya Pradesh, and Karnataka and in the
surrounds the core zone. It is managed to foot Himalayas and Chhotnagpur plateaus.
accommodate, a greater variety of resources and Besides, panthers, wolves, bears, deer. Antelopes,
support educational activities and research. bisons etc. live in almost all forests of India. Ibex types
(3) The transition zone : It is the outermost part of the of wild goats with long furs are found in Kashmir.
biosphere reserve. In this zone, there is active Musk-deer and yaks are found in the Himalayan region
co-operation between the reserve management in the borders of India and Nepal. Neel-gay is seen in
and the local people and activities like settlement, Uttar Pradesh and Madhya Pradesh. In our forests
cropping, forestry, recreation, etc. continue to different kinds of venomous snakes like python, cobra
take place. etc. are also found. In almost all our forests live
The reasons for the extinction of biodiversity monkeys, hares, jackals, foxes etc.
can be explained under following headings— Varieties of birds are seen in our forests, the most
(i) Habitat Fragmentation: The large natural important of which are the peacock, cuckoo, myna,
habitats of wildlife have been fragmented horn-bill (kochila khai), kite, vulture, hawk etc. Swans,
into small pieces due to urbanization, which
ducks, crows, golden oriole, cranes, doves etc. are
has caused many animals to shift from one
found almost everywhere. Tiger is our national animal
place to another which resulted in their
and peacock, the national bird. The number of wild
limited existence.
(ii) Introduction of Alien or Exotic Species: animals is gradually diminishing as our forests are
Alien species are often introduced diminishing.
inadvertantly for their economic and other Preservation of Wildlife :
uses. They often become invasive and drive The Government of India have forbidden hunting of
away the local species. birds and animals and declared it punishable under law
(iii) Co-extinction: Extinction of one species as the number of many kinds of wildlife diminishes
leads to the extinction of other species beyond expectation. Many plans are being executed for
dependent on it, e.g., when a small fish gets preservation of wildlife.
extinct, then the superior creatures There are at present 20 national parks and 190 wildlife
depending on it for their food also start to get sanctuaries in different States of India for preservation
extinct. of wildlife. In 1972 the Indian Wildlife Board launched
(iv) Pollution: The main reason for decrease in a national scheme called the “Project Tiger” to protect
animal population is pollution, due to which the tiger population.
many species of a group are effected. This tiger project ensures complete protection to the
(v) Habitat Destruction: Due to increase in tiger species in seven specially selected reserves at
population, there is human interference in the Manas (Assam), Palamau (Bihar), Similipal (Odisha),
natural habitat of wildlife, due to which their the Corbett National Park (U.P.), Melghat
habitat have been destroyed leading to (Maharashtra), Manipur (Karnataka) and Sundar-bans
shortage in biodiversity. This damage has
 133

(West Bengal). The other vanishing species like the example, only about one quarter of known threatened
rhinoceros and the lion are preserved in the Kaziranga plants are protected in conservation reserves. Some
National Park of Assam and the Gir Forests of Gujarat threatened species are confined to small areas of bush
respectively. and native grasslands in cities, farms and even along
In Odisha the Candace Forests near Bhuvaneswar have the sides of roads and railway lines.
been declared as Elephant Reserve and Chalice Lake as In some areas, farms are vital to the conservation of
the Bird Sanctuary. There are crocodile sanctuaries at threatened species. There are ways to manage farmland
Satkosia of Tikarpada and Bhitar Kanika (Cuttack to protect native plants and animals, and minimise land
District) now Kendrapara District. degradation. These also contribute to more productive
Q. 3. What are threatened species? Explain different meth- and sustainable agriculture.
ods to conserve them. (2020) Control exotic plants and animals : Non-native
Ans: Threatened species : Please see the answer of short plants and animals are ones that come from outside
answer type question-18. your local area.
Methods to conserve threatened species : Some Many parks and reserves, beaches, headlands and
methods are as following : inland waterways are infested with exotic weeds and
Conserve habitats in reserves : One of the most native species are disappearing because of this.
important ways to ensure that threatened plants and Blackberries infest temperate forests and streamside
animals survive is to permanently protect their habitats vegetation, bitou bush covers the dunes of east coast
in national parks, nature reserves or wilderness areas. beaches, and mimosa is threatening tropical wetlands.
National parks enable people to enjoy the beauty and A lot of exotic weeds come from people's gardens,
diversity of species without harming them. often because seeds get taken into the bush by the wind
When you visit a national park, observe the wildlife or birds.
codes: follow fire regulations; leave your pets at home; Many of the introduced animals particularly foxes and
do not pick flowers or remove bush rocks; leave birds' cats, are very efficient killers. Feral cats hunt a variety
eggs in their nests; and put your rubbish in a bin or of other small animals and climb trees or enter burrows
better still, take it home. to catch their prey. Sporting and aquarium fish have
Conserve habitats on farms : Despite the number of displaced native fish in rivers. Introduced animals such
national parks and nature reserves, many native plants as rabbits eat the food of native animals and even live
and animals are still inadequately protected. For in their burrows.

NCERT Fully Solved Exercise

Q.1 Name the three important components of biodiversity. (a) Speciation (formation of a new species) is a time
Ans. The three important components of biodiversity are — taking process. During the long course of
(i) Genetic diversity : Diversity at the level of genetic evolution, temperate regions have been subjected
differences. to frequent glaciations. On the other hand, the
(ii) Species diversity: The diversity at the species tropical latitudes have remained relatively
level. undisturbed.
(iii) Ecological diversity: The diversity at the (b) Tropical climate, unlike temperate ones, is less
ecosystem / ecological level. seasonal and therefore is relatively more constant.
Q.2 How do ecologists estimate the total number of species Such conditions help in niche specialisation and
present in the world ? lead to a greater species diversity.
Ans. Ecologists make a statistical comparison of the (c) There is more solar energy available in the tropics,
temperate-tropical species richness of an exhaustively which contributes to higher productivity. This
studied group of insects and extrapolate this ratio to higher productivity can support a larger number
other groups of animals and plants to come up with a of species.
gross estimate of the total number of species on earth. Q.4 What is the significance of the slope of regression in a
Q.3 Give three hypotheses for explaining why tropics show species – area relationship ?
greatest levels of species richness. Ans. The slope of regression in a species area relationship
Ans. Three important hypothesis in this regard are — suggests that, the richness of the species (biodiversity)
134

increases with increase in the explored area, up to a Q.7 What are sacred groves? What is their role in
certain limit. conservation ?
It was found that the value of slope (Z) ranges between Ans. In many cultures, tracts of forest are set aside, and all
0.1 to 0.2. This does not depend upon the area and the the trees and wildlife within are venerated and given
taxonomic group ( i. e., Z value or slope of the line is total protection. Such areas are called sacred groves.
similar for all taxonomic group and its value lies These are commonly found in Khasi and Jaintia Hills in
between 0.1 to 0.2). But for very large area (say for an Meghalaya and Aravalli Hills of Rajasthan.
entire continent), the slope is much steeper and the Q.8 Among the ecosystem services are control of floods
value of Z is 0.6 to 1.2. For example — for fruit eating and soil erosion. How is this achieved by the biotic
frugivorous birds and mammals in the tropical forests components of the ecosystem ?
of different continents, the slope value (Z value) is Ans. The biotic components of an ecosystem, particularly
about 1.15. plants play an important role in controlling floods and
Q.5 What are the major causes of species losses in a soil erosion. The roots of plants hold the soil particles
geographical region ? together, thereby preventing the top layer of the soil to
Ans. Following are the major reasons for the loss of get eroded by wind or running water. The roots also
biodiversity in a geographical reason. make the soil porous, thereby allowing ground water
(a) Habitat Loss and Fragmentation : When people infiltration and preventing floods. Hence, plants are
cut down trees, fill a wetland, plough grassland or able to prevent soil erosion and natural calamities such
burn a forest, the natural habitat of a species is as floods and droughts. Some microorganisms and
changed or destroyed. This habitat loss is the worms also make the soil fertile, this helps in the
primary cause of loss of biodiversity. growth small plants and grass which also make a
(b) Disturbance and Pollution : Natural disturbances protective cover on the top layer of soil.
and calamities, such as fire, tree fall, and Q.9 The species diversity of plants (22 per cent) is much
defoliation by insects severely affect less than that of animals (72 per cent). What could be
bio-communities. These can destroy biodiversity the explanations to how animals achieved greater
on a very large basis. diversification ?
(c) Introduction of Exotic Species : New species Ans. More than 72 per cent of species recorded on the Earth
(exotic species), when enter a geographical are animals and only 22 per cent species are plants.
region, have drastic effects on existing species This is because animals are mobile and have greater
(endemic species). These species may cause senses. They have adapted themselves effectively to
disappearance of existing species through ensure their survival in changing climatic conditions.
changed biotic interactions. They are more diverse and distributed to variety of
Q.6 How is biodiversity important for ecosystem habitats because of their greater motility compared to
functioning ? plants.
Ans. An ecosystem with high species diversity is more Q.10 Can you think of a situation where we deliberately
stable than an ecosystem with low species diversity. want to make a species extinct? How would you justify
High species diversity keeps the ecosystem in it?
equilibrium with the environment. Ecosystem becomes Ans. Yes, there are various kinds of parasites and
more productive, more tolerant and more resistant to disease-causing microbes that we deliberately want to
natural disturbances. eradicate them. Scientists have tried hard to eradicate
The ecological balance in such ecosystems is perfect small pox virus. Similarly, HIV is so deadlier that we
and does not get affected with smaller disturbances. want to completely eradicate this from this world.
ccc

Note : Due to Covid-19 Chapter-16 (Environmental Issues) is not in the Latest

Syllabus 2020-21.
 Chapter

16 ENVIRONMENTAL
ISSUES

(This Chapter has been Deleted From Syllabus For Session

2020-21 Due To COVID-19 Epidemic)
 136

Unsolved Paper-1 (Based on 30% less syllabus)

Biology-XII
Time : 3 hrs. 15 mins. M.M: 70

Instructions
(i) First 15 minutes are allotted for reading the question paper.
(ii) All questions are compulsory.
(iii) Please clear your answer with labelled diagram if required.
(iv) The fixed marks of all questions are mentioned in front of them.

1. Choose the correct option and write in your answer (d) Differentiate the following and give examples of
sheet. each: 1½ + 1½
(i) Human egg is: 1 (i) Innate and Acquired immunity
(a) Alecithal (b) Mesolecithal (ii) Active and Passive immunity
(c) Megalecithal (d) Telolecithal 5. (a) Write short notes on: 1½ + 1½
(ii) DNA sequences that code for protein are known (i) Use of microbes in fermented milk
as: 1 (ii) Use of microbes in industry.
(a) Interon (b) Differentiate the following 1½ + 1½
(b) Exons (i) RNA and DNA
(c) Control regions (ii) J-shaped population and S-shaped population
(d) Intervening sequences growth.
(iii) An insect repellent neem product is: 1 (c) Describe the commensalism and mutualism. 3
(a) Rotenone (b) Azadirachtin (d) What is mycorrhiza? Describe its utility. 3
(c) Parathion (d) Endrin 6. (a) With a neat, labelled diagram, describe the parts
(iv) Polyembryony was discovered by: 1 of a flower. 3
(a) Leeuwenhoek (b) Maheshwari (b) A teacher wants his/her students to find the
genotype of pea plants bearing purple coloured
(c) Nawaschin (d) Drouchet
flowers in their school garden. Name and explain
2. (a) Give two example of water pollinated plant. 1
the cross that will make if possible. 3
(b) Who coined the term gene? 1
(c) Explain sex determination in honeybees. 3
(c) Name the virus which causes AIDS. 1
(d) Why is using tobacco in any form injerious to the
(d) What is the shape of exponential growth curve? 1
health? Explain. 3
(e) Name any two threatened animal species of India.
7. Write a note on events of sexual reproduction. 5
1
Or
3. (a) What is semen? 2
Describe the alternation of generation and explain the
(b) Draw the structure of the initiator t-RNA adaptor
life cycle of angiospermic plants with the help of
molecule. 2
labelled diagram. 2+ 3
(c) What is full form of MABP? 2
8. Describe the process of DNA replication. 1+ 4
(d) What is habitat? 2
Or
(e) Define biodiversity. Name any one component of
What do you mean by sex-linked characters? Discuss
biodiversity. 2
its types and explain the inheritance of colour blindness
4. (a) Draw a labelled diagram of human sperm. 3
with example. 2+2+1
(b) Explain family planning and give its two methods.
9. What do you understand about immunity? Name two
2+½+½
human vaccines and clarify their importance. 1+ 2 + 2
(c) What is Down’s syndrome? Give its symptoms
Or
and cause. 3
What is ecological efficiency? Explain its significance .
2+ 3
 137

Unsolved Paper-2 (Based on 30% less syllabus)

Biology-XII
Time : 3 hrs. 15 mins. M.M: 70
Instructions : As model paper 1.
1. Choose the correct option and write in your answer (c) What is pathogen? Write down the names of
sheet: pathogens causing typoid fever and common cold
(i) One of the most invasive weed also called ‘terror in man and also symptoms of these disease. 3
of Bengal’ is: 1 (d) Make a chart (with diagrammatic representation)
(a) Lantana camara (b) Water hyacinth showing a restriction enzyme,the substrate DNA
(c) Carrot grass (d) All of these on which it acts the site at which it cuts DNA and
(ii) Crossing-over occurs between two homologous
the product it produces. 3
chromosomes in: 1
(a) Leptotene (b) Diplotene 5. (a) Amniocentesis for sex determination is banned in
(c) Pachytene (d) Zygotene our country. Is this ban necessary? Comment. 3
(iii) Occur in antiserum : 1 (b) Write short notes on anemophily. 3
(a) Antigen (b) WBCs (c) Difference between: 1½ + 1½
(c) Antibody (d) RBCs (i) Infectious and non-infectious diseases
(iv) Restriction enzymes are also known as: 1 (ii) Embryo sac and Endosperm.
(a) Carriers (b) Molecular scissors (d) Make diagram of transverse section of mature
(c) Vectors (d) Molecular markers anther. 3
2. (a) Who is the father of Indian embryology? 1 6. (a) Write short notes on: 1½ + 1½
(b) Name the stage of cells division where (i) Hot spots of biodiversity
segregation of an independent pair of (ii) Biosphere reserves
chromosome occurs. 1 (b) Write difference between: 1½ + 1½
(c) Who gave chromosomal theory of inheritance? 1 (i) Homozygous and heterozygous
(d) Which test is done for diagnosis of typhoid? 1 (ii) Genotype and phenotype
(e) State the type of interaction that exists between
(c) Why is that once a person starts taking alcohol or
ticks and dogs. 1
drugs, it is difficult to get rid of this habit? Discuss
3. (a) Write short note on ABO blood group? 1+1
(b) A garden pea plant produced axial white flowers. it with your teacher. 3
Another of the same species produced terminal (d) Why is the Human Genome Project called a maga
violet flowers. Identify the dominant traits. 2 project? 3
(c) Who proposed central dogma of molecular 7. Define the term ‘‘Reproduction’’. Why reproduction is
biology? Write the central dogma of molecular essential for organisms. 1+ 4
biology. 1 +1 Or
(d) Name the plant source of ganja. How does it affect Which blood groups are found in human beings?
the body of the abuser? 1+1 Explain the inheritance of blood groups. 2½ + 2½
(e) What is symbiosis? What is the shape of 8. Explain the usefulness of DNA fingerprinting in favour
exponential growth curve? 1+1 of human beings. 5
4. (a) Draw a labelled diagram of seed. 3
Or
(b) A pedigree chart given below presents a particular
What defense system found in our body to prevent the
generations which shows a trait irrespective of
sexes (i. e., parents in both male and female). infection? Explain special defense system in brief?
Neither of the parents of the particular generations 3+2
shows the trait. Draw your conclusion on the basis 9. Explain main steps involved in DNA recombination
of the pedigree. 3 technology and give its two beneficial uses. 3+2
Or
What is biodiversity? Write two procedures for its
preservation? 1+ 4
 138

Unsolved Paper-3 (Based on 30% less syllabus)

Biology-XII
Time : 3 hrs. 15 mins. M.M: 70
Instructions : As model paper 1.
1. Choose the correct option and write in your answer 5. (a) Write short notes on: 1½ + 1½
sheet: (i) Project Tiger
(i) Blastula of mammals is called: 1 (ii) Enzyme
(a) Blastodisc (b) Blastocyst (b) Difference between. 1½ + 1½
(c) Discoblastula (d) Coeloblastula (i) Self pollination and cross pollination.
(ii) Crick one of the discoverer of DNA double helical (ii) Hypocotyl and epicotyl.
structure was the man of: 1 (c) What is the use of biotechnology in agriculture
(a) Physics (b) Chemistry sector? 3
(c) Zoology (d) Botany (d) Draw a diagram of molecular structure of DNA. 3
(iii) Which of the following is a viral infection? 1 6. (a) Draw a labelled diagram of a section through
(a) Malaria (b) Typhoid ovary. 3
(c) Ringworm (d) Common cold (b) Why DNA is called genetic material? 3
(iv) Cosmids are obtained from : 1 (c) Define adolescence and discuss its problems. 3
(a) Bacteria (b) Viruses (d) You have identified a useful gene in a bacteria.
(c) Fungi (d) Plants Make a flow chart of the steps that you would
2. (a) Name the parts of gynoecium which develop into follow to transfer this gene to a plant. 3
fruit and seeds. 1 7. Describe the Mendel’s genetic law. Explain the
(b) Name any two Mendelian disorders. 1 dihybrid cross between the round-yellow and
(c) Give name of two human diseases which spread green-wrinkled seeded pea plants. 2+3
by sexual reproduction. 1 Or
(d) Name two diseases against which genetically Explain the usefulness of DNA fingerprinting in favour
engineered vaccine are now available. 1 of human beings. 5
(e) Write two examples of National parks of India. 1 8. A heavily bleeding and bruised road accident victim
3. (a) What is placenta? Give its one function. 2 was brought to a nursing home. The doctor
(b) Draw a flow chart of components of an Operon. 2 immediately gave him an injection to protect him
(c) Name any two types of cells that act as cellular against a deadly disease. 5
barriers to provide innate immunity in humans. 2 (i) Write what did doctor inject into the patient’s
(d) Define gene gun. 2 body?
(e) What is turner's syndrome? 2 (ii) How do you think this injection would protect the
4. (a) In our society the woman are often blamed for patient against the disease?
giving birth to daughters. Can you explain why (iii) Name the disease against which this injection was
this is not correct? 3 given and the kind of immunity it provides.
(b) Make a chart (with diagrammatic representation) 1½ + 1½ + 2
showing a restriction enzyme, the substrate DNA
on which it acts the site at which it cuts DNA and Or
the product it produces. 3 Explain main steps involved in DNA recombination
(c) Differentiate the following: 1½ + 1½ technology and give its two beneficial uses. 3+2
(i) T-cells and B-cells. 9. Write an essay on wild animals of India. 1+ 4
(ii) Infectious and Non-infectious diseases Or
Describe various morphological adaptations of
(d) Why are small birds like humming birds not found
xerophytic plants. 1+ 2 + 2
in polar regions? 3
 139

Unsolved Paper-4 (Based on 30% less syllabus)

Biology-XII
Time : 3 hrs. 15 mins. M.M: 70
Instructions : As model paper 1.
1. Choose the correct option and write in your answer (ii) Heterochromatin and Euchromatin
sheet: 5. (a) Give characteristics of insect pollinated flowers. 3
(i) Synergids are: 1 (b) What are the major components of seminal
(a) Haploid (b) Diploid plasma? 3
(c) Triploid (d) Tetraploid (c) Write short notes on: 1½ +1½
(ii) Har Gobind Khorana is Known for : 1 (i) Transcription
(a) Protein synthesis (ii) Double fertilization
(b) Discovery of RNA (d) Write difference between: 1½ +1½
(c) Discovery of DNA (i) Population and community
(d) Discovery of DNA liagse enzyme. (ii) Self pollination and cross pollination
(iii) Which body organ is severely affected in 6. (a) Comment on the RCH programme of the
jaundice? 1 government to improve the reproductive health of
(a) Heart (b) Brain people. 3
(c) Kidney (d) Liver (b) Work out F1 and F2 generations to explain the
(iv) Term ecology was coined by : 1 inheritance of flower colour in Pisum sativum.
(a) Robert brown (b) Elton Give phenotypic ratio (start with pure breeding). 3
(c) Haeckel (d) Reiter (c) List three major functions of a gene/ genetic
2. (a) Which cell organelle help in the formation of material. 3
acrosome? 1 (d) What do you mean by contraception? Give the
(b) Define a codon. 1 name of natural methods of contraception.
(c) Name two STDs. Which can be transmitted 1½ +1½
through contaminated blood. 1 7. Distinguish between spermatogenesis and oogenesis. 5
(d) What is humus? 1 Or
(e) Who is the father of Indian embryology? 1 What is genetics? Describe two Mendel’s law of
3. (a) What is placenta? 2 inheritance with example. 1+2 +2
(b) Mention any two autosomal genetic disorders 8. What is DNA? Describe its structure. Give the
with their symptoms. 2 difference between RNA and DNA. 1+2 +2
(c) Draw a structure of antibody with labelling. 2 Or
(d) What is meant by gene cloning? 2 Explain the term disease. Describe causative agents,
(e) Why green plants are not found beyond a certain symptoms and preventive measures of any two diseases
depth in ocean? 2 given below: 1+2 + 2
4. (a) Is sex education necessary in schools? Why? 3 (i) AIDS (ii) Chikungunya
(b) Why is the Human Genome Project called a mega (iii) Dysentery (iv) Meningitis
project? 3 9. Compare Chemical fertilizer and Biofertilizer. Prove
(c) In metropolitan cities of India, many children are that to maintain the fertility of soil and quality of crops,
suffering from allergy/asthma. What are the main Biofertilizer is more useful. 2+3
causes of this problem. Give some symptoms of Or
allergic reactions. 3 Define biotechnology. Explain application of
(d) Difference between: 1½ +1½ biotechnology in production of Bt cotton. 1+ 4
(i) RNA and DNA
 140

Unsolved Paper-5 (Based on 30% less syllabus)

Biology-XII
Time : 3 hrs. 15 mins. M.M: 70

Instructions : As model paper 1.

1. Choose the correct option and write in your answer (i) Wilting
sheet: (ii) Mangrove plants
(i) Birds are: 1 (b) What is community interaction? Give its type and
(a) Oviparous (b) Viviparous examples. 2+½ +½
(c) Ovoviviparous (d) All of these (c) Write down the differences between
(ii) Number of homologous chromosomes in human commensalism and parasitism. 3
sperm are: 1 (d) Which gases are present in Biogas, give their
(a) 23 (b) 46 name? Give two benefits of Biogas for man. 2+1
(c) 1 (d) Nil 6. (a) When a cross is made between tall plant with
(iii) Antibodies are produced by: 1 yellow seeds (Tt Yy) and tall plant with green
(a) Leucocytes (b) Lymphocytes seed (Tt yy), what proportions of phenotype in the
(c) Erythrocytes (d) None of these offspring could be expected to be: 1½ + 1½
(iv) Tiger is not a resident in the National Park: 1 (i) Tall and green
(a) Sunderbans (b) Gir (ii) Dwarf and green
(c) Jim Corbett (d) Ranthambore (b) Give the name of four viral diseases found in man
2. (a) Who is the father of Indian embryology? 1 and also give the infectious method any one
(b) Universal recipient person belong to which blood disease. 2 +1
group? 1
(c) Write down a short note on Allen's rule. 3
(c) Who gave the chromosomal theory of (d) Write short note on red data book. 3
inheritance? 1
7. What is gene cloning? Explain the different steps used
(d) Give the name of functional unit of gene. 1
in gene cloning. 1+ 4
Or
(e) Give an example of rod-shaped virus. 1
Draw a labelled diagram of human male reproductive
3. (a) Define genetics and who is known as the father of
system showing various reproductive glands. 5
modern genetics? 2
8. Explain the term disease. Describe causative agents,
(b) Difference between DNA and RNA. 2
symptoms and preventive measures of AIDS,
(c) What are interferons? Give the scientific name of
chikungunya, dysentery and meningitis. 1+ 4
causative agent of disease malaria. 2
Or
(d) Mention the uses of cloning vector in
Explain the structure of DNA model given by Watson
biotechnology. 2 and Crick and its work. Explain the Biological
(e) What is fermentation? Give its two uses. 2 significance of this model. 3+2
4. (a) What is polyembryony? how many types it? 1+2 9. Compare the chemical fertilizer and biofertilizer. Prove
(b) How is sex determined in human beings, show it that to maintain the fertility of soil and quality of crops,
with graphical diagram. 3 biofertilizer is more useful. 1+ 4
(c) Write a short note on gel electrophoresis. 3 Or
(d) Differentiate the following: 1½ + 1½
What is pollination? Describe verious kinds of
(i) Homozygous and Heterozygous
pollination that occur in flowering plants. Mention
(ii) Genotype and Phenotype.
about the biotic pollinating agents. 1+ 2 + 2
5. (a) Write the short note. 1½ + 1½
 141

Some Important Diagrams

Stigma Pistil/carpel
Stamen Style
Anther Ureter
Filament Ovary
Seminal vesicle

Urinary bladder

Vas deferens
Ejaculatory
Prostate duct

Petal Penis
Gut
Sepal (rectum)
Urethra

Ovule Glans
Testis Bulbo-urethral
Pedicel
Scrotum (Cowper’s) gland
Structure of flower (bisexual), showing male and female organs
Male reproductive system

Urinary
bladder
Vas deferens Vas deferens
tied and cut tied and cut

Prostate
Seminal
vesicle Cowper’s
gland
Urethra
Vas deferens
Epididymis
Various types of pollination
Testis

Scrotum

Penis

Vasectomy

Pollen tube

HIV (Human
immuno-deficiency virus)
Pollen tube entering an ovule
142

Spermatozoa

Spermatid

Secondary
spermatocyte

Primary
spermatocyte

Sertoli cell

Spermatogonium

Sectional view of a seminiferous tubule

Fallopian tube Fallopian tube

tied and cut tied and cut

Ovary Fimbriae
Endometrium
Myometrium
Internal os
Cervix
External os
Vagina

Tubectomy

Hershey-Chase experiment (Transduction)

Path of sperm and ovum and place of fertilisation

 143

Simple stirred tank bioreactor (STB)

Clover-leaf model of tRNA

A simple food web in a grassland ecosystem

Clean air

Discharge corona
Negatively charged
wire
Water/lime
spray
Dirty air Clean
air

Dirty Dust particles

Particulate
air Collection plate grounded
matter
Electrostatic precipitator
Scrubber
Electrostatic precipitator

Homology in the structure of forearm of different vertebrates

144