PYQ

1) Newly formed DNA copies may not be identical at times. Give one reason. (AI2017)
Answer:
When a cell reproduces, DNA replication occurs which results in formation of two similar copies
of DNA. The process of copying the DNA leads to some variations each time

2) What is DNA? (Delhi 2016, Foreign 2015)

Answer:
DNA (deoxyribonucleic acid) is a polymer made up of large number of nucleotide units. It carries
genetic information from generation to generation.

3) Reproduction is one of the most important characteristic ‘of living beings. Give three reasons
in support of the statement. (AI 2017)
Answer:
Reproduction is one of the most important characteristics of living beings because :

 it is essential for existence and continuity of a species.

 it helps to pass genetic information to next generation.
 it brings variations in next generation which is the basis for evolution.

4) What is the effect of DNA copying, which is not perfectly accurate, on the reproduction
process? How does the amount of DNA remain constant through each new generation is a
combination of DNA copies of two individuals? (AI 2014)
Answer:
In the process of reproduction, if DNA copying is not perfectly accurate, variation occurs. These
in turn may allow few individuals of a population to survive in an altered niche and becomes the
basis of evolution and over time. Such variations are useful for the survival of species.
The combination of DNA copies of two individuals, (male and female) occurs during sexual
reproduction. Reduction division (meiosis) during gamete formation halves the chromosome
number in both male and female gametes.

5) How does Plasmodium reproduce. Is this method sexual or asexual? (Delhi 2017)
Answer:
Plasmodium reproduces through multiple fission method. In this method, the parent organism
splits to form many new organisms at the same time. This is an asexual method of reproduction.

6) Name the method by which Spirogyra reproduces under favourable conditions. Is this method
sexual or asexual? (Delhi 2017)
Answer:
The method by which Spirogyra reproduces under favorable conditions is fragmentation. This is
an asexual mode of reproduction

7) What happens when a Planaria gets cut into two pieces? (Delhi 2016)
Answer:
When Planaria is cut into two pieces then each piece grows into a complete organism. This is
known as regeneration.

8) Write two differences between binary fission and multiple fission in a tabular form. (Delhi
2015)
Answer:
Differences between binary fission and multiple fission are as follows:

Binary fission Multiple fission

(i) The parent organism, splits to form two new The parent organism splits to form many new

organisms, e.g., Amoeba, Paramecium. organisms at the same time, e.g., Plasmodium.

(ii) The nucleus of the parent body divides only The nucleus of the parent body divides repeatedly to

once to produce two nuclei. produce many nuclei.

9) List four advantages of vegetative propagation. (Delhi 2014)

Answer:
The following are the advantages of vegetative propagation:

 The characters of the parent plants are preserved hence a good variety produced can be
propagated by vegetative means.
 The plants, which do not produce viable seeds or produce very few seeds, can be
reproduced by this method. For example, banana, potato, grapes, sugarcane, rose,
orange, etc.

10) List four modes of asexual reproduction. (Delhi 2014)

Answer:
The four modes of asexual reproduction are :

 binary fission
 budding
 regeneration and
 vegetative propagation.

11) Draw labelled diagrams to illustrate budding in Hydra. (AI 2014)

Answer:
The given diagram illustrates budding in Hydra:

12) List two advantages ofvegetative reproduction practised in case of an orange plant. (Delhi
2012)
Answer:
The two advantages of vegetative propagation practised in case of an orange plant are :

 The new plants produced by vegetative propagation will be exactly like the parent plant.
Therefore, any desirable features of the parent plant will be replicated in the new plants.
 The orange plants that have lost the capacity to produce seeds, can also be propagated.

13) Name an organism which reproduces by spore formation. List three conditions favourable
for spores to germinate and grow. (AI 2012)
Answer:
Rhizopus reproduce by the method of spore formation.
The three conditions favourable for spores to germinate and grow are moisture, suitable
temperature and food (nutrition).

14) What happens when

(a) accidently, Planaria gets cut into many pieces-
(b) Bryophyllum leaf falls on the wet soil
(c) on maturation sporangia of Rhizopus bursts? (Delhi 2017)
Answer:
(a) When Planaria accidently gets cut into many pieces then its each piece grows into a
complete organism. This is known as regeneration.
(b) When the Bryophyllum leaf falls on the wet soil, the buds present in the notches along the
leaf margin develop into new plants. This is known as vegetative propagation.
(c) The sporangia of Rhizopus contain cells or spores that can eventually develop into new
Rhizopus individuals when it bursts on maturation.

15) Explain the term “regeneration” as used in relation to reproduction of organisms. Describe
briefly how regeneration is carried out in multicellular organisms like Hydra. (AI 2016)
Answer:
The process of formation of entire organism from the body parts of a fully differentiated
organism is called regeneration. It occurs by process of growth and development.
Simple animal like Hydra shows regeneration. When a small piece of Hydra breaks off it grows
into complete new Hydra.
During regeneration, the cells of cut body part of the organism divide rapidly to make a mass of
cells. The cells here move to their proper places within the mass where they have to form
different types of tissues. In this way complete organism is regenerated.
16) Explain the process of regeneration in Planaria. How is this process different from
reproduction? (Foreign 2015, AI 2014)
Answer:
Planaria possesses great power of regeneration. If the body of Planaria somehow gets cut into
a number of pieces, then each body piece can regenerate into a complete Planaria by growing
all the missing parts. This is shown in following figure:

17) List any two modes of asexual reproduction in animals. Under which mode of reproduction
is vegetative propagation placed and why? List two advantages of vegetative propagation. (AI
2014)
Answer:
The two modes of asexual reproduction in animals are : (i) fission and (ii) fragmentation.
Vegetative propagation is placed under asexual mode of reproduction because in this mode
new plants are obtained from the parts of old plants (like stems, roots and leaves), without the
help of any reproductive organs

18) With the help of suitable diagrams, explain the various steps of budding in Hydra. (AI 2011)
Answer:
In multicellular organisms, such as Hydra, a small protuberance arises from one side of the
body. The protuberance grows and develops adult like structure. In Hydra, it develops a
hypostome and tentacles at its free end. It develops a basal disc at the point of attachment with
the parent organism and finally gets detached to lead an independent life

19) (a) What is spore formation?

(b) Draw a diagram showing spore formation in Rhizopus.
(c) List two advantages for organisms to reproduce themselves through spores. (Foreign 2011)
Answer:
(a) Spore formation is the process of formation of microscopic reproductive structures called
spores. These spores when detaches from the parent gives rise to a new individual.
Reproduction by the formation of spores is a common method of asexual reproduction in some
bacteria and most of the fungi.
(b) Following figure shows the process of spore formation in Rhizopus:

(c) Two advantages to spore producing organism are as follows:

 Spores help organism to survive harsh environmental conditions as spores are covered by
thick walls which protect them until they come in contact with moist surface and germinate.
 Spores are generally very small and light. Therefore, it ensures easy dispersal by wind,
water and animal.

20) Why is fertilisation not possible without pollination? (Foreign 2016)

Answer:
The process of pollination (in plants) ensures that male gametes bearing structure called pollen
comes in contact with the female reproductive structure of the plant. Once the male and female
gametes are in close vicinity, they fuse and fertilisation is accomplished.

21) What is the main difference between sperms and eggs of humans? Write the importance of
this difference. (AI 2014)
Answer:
The main difference between sperms and eggs of humans is that a sperm has X or Y
chromosome whereas egg has X chromosome. This helps in determination of the sex of a
person and maintaining the genetic continuity in the organisms.

22) State the role of placenta in the development of embryo. (AI 2012)
Answer:
Placenta is a physiological connection between an embryo and uterine wall of the mother
through which nutrients and other useful substances enter into fetus from mother’s blood and
waste products like urea and carbon dioxide are expelled into mother’s blood from fetus.

23) Describe the role of fallopian tubes in the female reproductive system. (AI2011)
Answer:
Fallopian tubes are a pair of elongated, ciliated, muscular and tubular structures extending from
close to ovaries to uterus. It is the site of fertilisation and helps in the conduction of ovum or
zygote towards uterus by ciliary action and peristalsis.

24) Define the term pollination. Differentiate between self-pollination and cross-pollination. What
is the significance of pollination? (2020)
Answer:
The process of transfer of pollen grains from anther of a flower to the stigma of the same flower
or another flower of the same species is known as pollination. The two inodes of pollination are
self pollination and cross pollination.
Differences between self pollination and cross pollination are as follows:

Character Self pollination Cross pollination

Occurs between two flowers of

Occurs within a flower or between
Occurrence two different plants of the same
two flowers of the same plant.
species.

External agents such as wind,

Usually no external agent of
Agent of pollination water, insects and birds are
pollination is required.
required.

Produced in small numbers, thus

Produced in large numbers thus,
Production of pollen grains no wastage of pollen grains
wastage of pollen grains occurs.
occurs.

Flowers are generally not Flowers are attractive with

Appearance of flowers
attractive. coloured petals

25) (a) What provides nutrition to human sperms? State the genetic constitution of a sperm.
(b) Mention the chromosome pair present in a zygote which determines the sex of (i) a female
child and (ii) a male child. (2020)
Answer:
(a) The secretions of seminal vesicles and prostate gland provides nutrition to the human
sperms and also make their further transport easier. The genetic constitution of a sperm can be
50% have X chromosome and 50% have Y chromosome.
(b) (i) XX – Female child
(ii) XY – Male child

26) State the changes that take place in the uterus when:
(a) Implantation of embryo has occurred.
(b) Female gamete/egg is not fertilised. (Delhi 2017)
Answer:
(a) Implantation is the close attachment of the blastocyst (young multicellular embryo) to the
uterine wall. It is followed by a number of developmental changes in the thickened wall of
uterus. An intimate connection between the fetal membrane and the uterine wall called placenta
is formed. This is a disc which is embedded in the uterine wall. The placenta serves as the
nutritive, respiratory and excretory organ of the fetus.

(b) When the female gamete/egg is not fertilised, this lining is not needed any longer. So, the
lining slowly breaks and comes out through vagina as blood and mucus. This cycle takes place
every month and is known as menstrual cycle.

27) Name the parts A, B and C shown in the following diagram and state one function of each.
(Delhi 2016)

Answer:
In the given figure, part A is anther, part B is style and part C is ovule.
Anther (A) is a part of male reproductive organ of flower called stamen. Large number of pollen
grains are formed inside anther. Style (B) and ovule (C) are parts of female reproductive organ
of flower called carpel / pistil. Style is a long conducting tube which gives the passage to pollen
tube carrying male gametes so that it reaches ovary which contains one or more ovules. Ovules
contain female gamete or egg. On fertilisation ovary converts into fruit and ovules give rise to
seeds.

27) Suggest three contraceptive methods to control the size of human population which is
essential for the health and prosperity of a country. State the basic principle involved in each.
(Delhi 2016)
Answer:
Three contraceptive methods which can help to control human population are:
(i) Condom : It is a mechanical barrier which does not allow sperms and ovum to meet, hence
prevents fertilisation. Condoms are made of thin rubber/latex sheath used to cover the penis in
the male and vagina/cervix in female just before coitus (intercourse) so that the ejaculated
semen is not released in the female reproductive tract.

(ii) Intrauterine devices (IUDs): These are devices inserted by doctors or expert nurses in the
uterus through vagina. These are presently available as non-medicated IUDs, copper releasing
IUDs (CuT, etc.) and hormone releasing IUDs. They increase phagocytosis of sperms within
uterus.
(iii) Oral pills : These pills contain progesterone alone or a combination of progestogen and
estrogen. They inhibit ovulation and make uterus unsuitable for implantation, hence prevent
fertilisation.

27) (a) List two reasons for the appearance of variations among the progeny formed by sexual
reproduction.

(i) Name the part marked A in the diagram.

(ii) How does A reaches part B?
(iii) State the importance of the part C.
(iv) What happens to the part marked D after fertilisation is over? (AI 2016)
Answer:
(a) Variations arise in sexually reproducing organisms on account of the following:
(i) Genetic variations occur of because DNA copying mechanism is not absolutely accurate.
(ii) Creation of new combinations of genetic variations because variations from two individuals
combine during fusion of gametes.

(b) (i) A is pollen grain.

(ii) Part B is stigma. It is the part of pistil (female reproductive organ) that receives pollen grains.
Pollen grains reach stigma through various agencies like wind, water, insect, etc.
(iii) Pollen tube (C) carries male gametes to the ovule present in ovary. Male gametes fuse with
egg and secondary nucleus to give rise to zygote and endosperm.
(iv) Female gamete (D) fuses with male gamete and converts to embryo after fertilisation.

28) What is sexual reproduction? List its four significances. (Foreign 2016)
Answer:
Sexual reproduction is the process of production of offspringby the fusion of male and female
gametes. Here, haploid gametes fuse to form diploid zygote which develop into a mature
organism.
Significance of sexual reproduction are as follows:

 Sexual reproduction gives rise to genetic variations because of genetic recombination that
takes place during fusion of gametes.
 Progenies arising through sexual reproduction sometimes show better combination of
traits and get better adapted to their surroundings.
 Genetic recombination, interaction, etc., during sexual reproduction provide vigour and
vitality to the offspring.
  Variations in genes play an important role in evolution.

29) (a) Mention the role of the following organs of human male reproductive system.
(i) Testes (ii) Scrotum (iii) Vas deferens
(iv) Prostate gland
(b) What are the two roles of testosterone? (Foreign 2016)
Answer:
(a) (i) Testes : The two testes in male are the sites where male gametes, i.e., sperms are
formed. Testes also produce the male sex hormone called testosterone.
(ii) Scrotum : The scrotum is a pouch of skin that lie outside abdominal cavity. The two testes lie
in respective scrotal sacs. The scrotum acts as a thermoregulator and provides an optimal
temperature for the formation of sperms.
(iii) Vas deferens : This is a straight tube, about 40 cm long, which carries the sperms to the
seminal vesicles, where mucus and a watery alkaline fluid containing fructose, mix with the
sperms.
(iv) Prostate gland : It is a single large gland that surrounds the urethra and produces a milky,
slightly acidic secretion. Secretion of prostate gland nourishes and activates the sperm to swim.

(b) Two roles of testosterone are:

(i) It plays a key role in development of male secondary sex organs such as prostate, etc.
(ii) It promotes the secondary sexual character-istics in males such as increased muscle and
bone mass, growth of body hair, etc

30) What are sexually transmitted diseases? List two examples each of diseases caused due to
(i) bacterial infection and (ii) viral infection. Which device or devices may be used to prevent the
spread of such diseases? (Delhi 2015)
Answer:
The diseases that are spread by sexual contact with an infected person are called sexually
transmitted disease (STDs).
(i) Bacterial infection causes gonorrhoea, syphilis.
(ii) Viral infection causes AIDS, genital herpes. STDs can be prevented by using male and
female condoms

31) List four points of significance of reproductive health in a society. Name any two areas
related to reproductive health which have improved over the past 50 years in our country. (AI
2015)
Answer:
The general awareness regarding reproductive health in a society is significant as :

 Maintenance of personal hygiene among youngsters and proper knowledge of their

reproductive parts helps them adjust with the physical changes and cope with emotional
disturbances.
 Reproductively healthy society must be free from the curse of child marriage which begets
many complications at the level of individual and society both.
 Proper care of expecting mothers, monitoring their health after child birth and care of new
born help in building a healthy society. In past 50 years, various areas related to
reproductive health have been launched which have improved the reproductive health of
our society in following ways: Two of them are :
 (i) reduced mortality rate of mother and infant
(ii) birth control due to easily available contraceptive and reduced STDs cases

32) Draw longitudinal section of a bisexual flower and label the following parts on it.
(i) Anther
(ii) Ovary
(iii) Stigma
(iv) Style (Foreign 2015)
Answer:
Longitudinal section of a bisexual flower is as follows:

33) What is placenta? Explain its function in humans. (Foreign 2015, AI 2014)
Answer:
Placenta is an intimate connection between fetus and uterine wall of the mother to exchange the
materials. It is a disc shaped structure embedded in the uterine wall.

Placenta performs the following functions:

 All nutritive elements from maternal blood pass into the fetus through it.
 Placental helps in respiration, i.e., supply of oxygen and removal of CO 2 from fetus to
maternal blood.
 Placenta also secretes hormone

34) Write names of those parts of a flower which serve the same function as the following do in
the animals
(i) testes
(ii) sperm
(iii) ovary
(iv) egg. (Delhi 2014)
Answer:
The parts of a flower which serve the same function as following do in the animals are
(i) testes – anther of stamen
(ii) sperm – pollen
(iii) ovary – ovary of pistil
(iv) egg – female germ cell present in ovule.
35) On the notice board of ultrasound clinics it is generally stated. “Here prenatal sex
determination and disclosure of sex (boy or girl before birth) of fetus is not done. It is prohibited
and punishable under law.”
(a) List two advantages of imposing ban on prenatal sex determination.
(b) What can students do to educate the society about the following?
(i) The ill-effects of indiscriminate female feticide.
(ii) Adopting small family norms. (Foreign 2014)
Answer:
(a) The two advantages of imposing ban on prenatal sex determination are
(i) check on female feticide
(ii) improving sex ratio in the country.

(b) Students should educate the society as that

(i) female feticide is reducing the number of girls drastically in some societies. For a healthy
society, the male-female sex ratio must be maintained at almost the same level. Due to reckless
female feticide, the male-female child sex ratio is declining at an alarming rate in some sections
of our society.

(ii) Children in a small family can be provided with all the resources from education, good
amenities like food, clothing and healthy life style. As the family grows larger, the resources
should be shared with increased number of member. Having fewer children also keeps the
mother in good health.

36) Name the two reproductive parts of a bisexual flower which contain the germ cells. State the
location and function of its female reproductive part. (Foreign 2014)
Answer:
The two reproductive parts of a bisexual flower which contain the germ cells are carpel (female
reproductive part) and stamen (male reproductive part). Carpel is situated in the centre of the
flower as a flask-shaped structure. A carpel is made up of three parts-stigma, style and ovary.
The distal part of a carpel is called stigma. Stigma is responsible for receiving pollen during
pollination. Style is an elongated tubular structure which connects stigma with ovary. The basal
swollen part of carpel is ovary. Ovary bears several ovules. After fertilisation ovules form seeds
and ovary forms the fruit.

37) What does HIV stands for? Is AIDS an infectious disease? List any four modes of spreading
AIDS. (AI 2011)
Answer:
HIV stands for Human Immunodeficiency Virus. Yes, AIDS is an infectious disease. It is
transmitted sexually or through exposure to contaminated blood.
Four modes of spreading AIDS are :

 unprotected sex with an infected partner

 use of contaminated needle and syringes
 use of contaminated razors for shaving

38) (a) In the female reproductive system of human beings, state the functions of:
(i) Ovary
(ii) Oviduct.
(b) Mention the changes which the uterus undergoes, when
(i) it has to receive a zygote.
(ii) no fertilisation takes place.
(c) State the functions of placenta. (2020)
Answer:
(a) (i) Tire ovaries in female are primary sex organs (or female gonads) which perform the dual
function – production of female gametes (eggs or ova) and secretion of female sex hormones
(estrogen and progesterone).
(ii) Oviducts or fallopian tube are paired tubes originating near to the ovaries of their respective
sides and extend upto uterus. The terminal part of fallopian tube is funnel-shaped with finger-
like projections called fimbriae lying near ovary. Fimbriae pick up the ovum released from ovary
and push it into fallopian tube. Fertilisation also takes place in the oviduct.

(b) (i) As the ovary releases one egg every month, the uterus also prepares itself, every month
to receive fertilised egg by making its lining thick and spongy to nourish the zygote if fertilisation
takes place.
(ii) When the female gamete/egg is not fertilised, this lining is not needed any longer. So, the
lining slowly breaks and comes out through vagina as blood and mucus through menstrual cycle
that takes place every month.

39) Draw a neat diagram showing fertilisation in a flower and label (a) pollen tube (b) Male germ
cell and (c) Female germ cell on it. Explain the process of fertilisation in a flower. What happens
to the (i) ovary and (ii) ovule after fertilisation? (2020)
Answer:
Diagram showing fertilisation in a flower:

Fertilisation, in plants, occurs when the male gamete present in pollen grain fuses with the
female gamete (or egg) present in ovule. When a pollen grain falls on the stigma of the carpel, it
bursts open and grows a pollen tube downwards through the style towards the female gamete in
the ovary. Male gametes move down the pollen tube. The pollen tube enters the ovule in the
ovary. The tip of pollen tube bursts and male gametes comes out of pollen tube. In ovary, the
male gamete of pollen combines with the female gamete or egg present in ovule to form a
fertilised egg.
After fertilisation,
(i) ovule develops into seed
(ii) ovary develops into fruit.

How Do Organisms Reproduce Class 10

40)

Important Questions with Answers Science

Chapter 8
July 15, 2022 by Sastry CBSE

We have given these Important Questions for Class 10 Science Chapter 8 How Do Organisms
Reproduce to solve different types of questions in the exam. Previous Year Questions &
Important Questions of How Do Organisms Reproduce Class 10 Science Chapter 8 will help the
students to score good marks in the board examination.

Important Questions of How Do Organisms

Reproduce Class 10 Science Chapter 8
Question 1.
Newly formed DNA copies may not be identical at times. Give one reason. (AI2017)
Answer:
When a cell reproduces, DNA replication occurs which results in formation of two similar copies
of DNA. The process of copying the DNA leads to some variations each time. As a result, the
DNA copies produced are similar to each other but sometimes may not identical.

Question 2.
When a cell reproduces, what happens to its DNA? (AI 2017)
Answer:
When a cell reproduces, DNA replication occurs which forms two similar copies of DNA..

Question 3.
What is DNA? (Delhi 2016, Foreign 2015)
Answer:
DNA (deoxyribonucleic acid) is a polymer made up of large number of nucleotide units. It carries
genetic information from generation to generation.

Question 4.
Name the life process of an organism that helps in the growth of its population. (AI 2015)
Answer:
Reproduction is a life process that helps in multiplication of an organism and growth of its
population.
Question 5.
Reproduction is one of the most important characteristic ‘of living beings. Give three reasons in
support of the statement. (AI 2017)
Answer:
Reproduction is one of the most important characteristics of living beings because :

 it is essential for existence and continuity of a species.

 it helps to pass genetic information to next generation.
 it brings variations in next generation which is the basis for evolution.

Question 6.
Define reproduction. How does it helps in providing stability to the population of species? (AI
2016)
Answer:
The production of new organisms by the existing organisms of the same species is known as
reproduction. It is linked to the stability of population of a species. DNA replication during
reproduction ensures transfer of specific characters or body design features that is essential for
an individual of a population to live and use that particular niche. Some variations present in a
few individuals of population caused due to reproduction which also helps in their survival at
changing niches.

Question 7.
What is DNA copying? State its importance. (Delhi 2015)
Answer:
DNA copying is the production of similar copies of DNA present in a cell using various chemical
reactions. DNA copying is essential for reproduction through which the organisms pass on their
body features to their offspring. Moreover, minor alternations during the process of DNA copying
result in the production of variations. Such variations are useful for the survival of species over
time.

Question 8.
What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process?
How does the amount of DNA remain constant through each new generation is a combination of
DNA copies of two individuals? (AI 2014)
Answer:
In the process of reproduction, if DNA copying is not perfectly accurate, variation occurs. These
in turn may allow few individuals of a population to survive in an altered niche and becomes the
basis of evolution and over time. Such variations are useful for the survival of species.
The combination of DNA copies of two individuals, (male and female) occurs during sexual
reproduction. Reduction division (meiosis) during gamete formation halves the chromosome
number in both male and female gametes. Since these two gametes fuse during fertilisation, the
original number of chromosomes (as in the parent) is restored in the offspring. By this way the
amount of DNA remains constant in each new generation.

Question 9.
Name the method by which Spirogyra reproduces under favourable conditions. Is this method
sexual or asexual? (Delhi 2017)
Answer:
The method by which Spirogyra reproduces under favorable conditions is fragmentation. This is
an asexual mode of reproduction.

Question 10.
How does Plasmodium reproduce. Is this method sexual or asexual? (Delhi 2017)
Answer:
Plasmodium reproduces through multiple fission method. In this method, the parent organism
splits to form many new organisms at the same time. This is an asexual method of reproduction.

Question 11.
Name the part of Bryophyllum where the buds are produced for vegetative propagation. (Delhi
2016)
Answer:
Bryophyllum propagates vegetatively by the buds produced at the margins of leaves.

Question 12.
What happens when a Planaria gets cut into two pieces? (Delhi 2016)
Answer:
When Planaria is cut into two pieces then each piece grows into a complete organism. This is
known as regeneration.

Question 13.
What happens when a mature Spirogyra filament attains considerable length? (AI 2016)
Answer:
When a mature Spirogyra filament attains considerable length it simply breaks into two or more
fragments and each fragment then grows into a new Spirogyra.

Question 14.
Name the method by which Hydra reproduces. Is this method sexual or asexual ? (Foreign
2016)
Answer:
Hydra generally reproduces through budding. It is an asexual method of reproduction.

Question 15.
Name two simple organisms having the ability of regeneration. (AI 2015)
Answer:
Hydra and Planaria are two organisms that have the ability to regenerate.

Question 16.
Name the causative agent of the disease “kala- azar” and its mode of asexual reproduction.
(Foreign 2015)
Answer:
Causative agent of the disease Kala-azar is Leishmania. It reproduces asexually by binary
fission.

Question 17.
Write two differences between binary fission and multiple fission in a tabular form. (Delhi 2015)
Answer:
Differences between binary fission and multiple fission are as follows:

Binary fission Multiple fission

(i) The parent organism, splits to form two new The parent organism splits to form many new

organisms, e.g., Amoeba, Paramecium. organisms at the same time, e.g., Plasmodium.

(ii) The nucleus of the parent body divides only The nucleus of the parent body divides repeatedly to

once to produce two nuclei. produce many nuclei.

Question 18.
List four modes of asexual reproduction other than fission in the living organisms. (Delhi 2014)
Answer:
The four modes of asexual reproduction other than fission in living organisms are :

 budding
 spore formation
 regeneration and
 fragmentation.

Question 19.
List four advantages of vegetative propagation. (Delhi 2014)
Answer:
The following are the advantages of vegetative propagation:

 The characters of the parent plants are preserved hence a good variety produced can be
propagated by vegetative means.
 The plants, which do not produce viable seeds or produce very few seeds, can be
reproduced by this method. For example, banana, potato, grapes, sugarcane, rose,
orange, etc.
 It is an easier, quicker and cheaper method of propagation.
 It is easier to get rid of pathogen from any part of plant by vegetative propagation.

Question 20.
List four modes of asexual reproduction. (Delhi 2014)
Answer:
The four modes of asexual reproduction are :
  binary fission
 budding
 regeneration and
 vegetative propagation.

Question 21.
Draw labelled diagrams to illustrate budding in Hydra. (AI 2014)
Answer:
The given diagram illustrates budding in Hydra:

Question 22.
How do Plasmodium and Leishmania reproduce? Write one difference in their mode of
reproduction. (Foreign 2014)
Answer:
Plasmodium and Leishmania reproduce by the process of fission which is an asexual mode of
reproduction. Plasmodium reproduces by multiple fission. About 1000 daughter cells are
produced by the multiple fission of a Plasmodium. Leishmania reproduces by the process of
binary fission. In Leishmania, the splitting of parent cell takes place in a definite plane
(longitudinally) with respect to flagellum at its end to produce two daughter cells.

Question 23.
Define multiple fission. Give its one example. (Foreign 2014)
Answer:
Multiple fission is an asexual mode of reproduction in which the parent organism splits to form
many new organisms at the same time. Multiple fission occurs in Plasmodium.

Question 24.
List two advantages ofvegetative reproduction practised in case of an orange plant. (Delhi 2012)
Answer:
The two advantages of vegetative propagation practised in case of an orange plant are :

 The new plants produced by vegetative propagation will be exactly like the parent plant.
Therefore, any desirable features of the parent plant will be replicated in the new plants.
 The orange plants that have lost the capacity to produce seeds, can also be propagated.

Question 25.
Name an organism which reproduces by spore formation. List three conditions favourable for
spores to germinate and grow. (AI 2012)
Answer:
Rhizopus reproduce by the method of spore formation.
The three conditions favourable for spores to germinate and grow are moisture, suitable
temperature and food (nutrition).
Question 26.
List two advantages of practising vegetative propagation in plants. Select two plants raised by
this method from the list given below : Banana, Gram, Pea, Rose, Tomato, Wheat (Foreign
2012)
Answer:
Two advantages of the vegetative propagation of plants are:

 Any desirable features of the parent plant can be replicated in the new plants.
 Flowers and fruits can be grown in a shorter time as compared to the plants grown from
seeds. The two plants raised by this method are banana and rose.

Question 27.
Write any two differences between binary fission and multiple fission in a tabular form as
observed in cells of organisms. (Delhi 2011)
Answer:
Refer to answer 17.

Question 28.
List any four reasons for vegetative propagation being practised in the growth of some type of
plants. (AI2011)
Answer:
Refer to answer 19.

Question 29.
What is vegetative propagation? Write two of its advantages. (Foreign 2011)
Answer:
Vegetative propagation is a method of asexual reproduction in plants in which the parts other
than seeds are used as propagules. Also refer to answer 26.

Question 30.
Write one main difference between asexual and sexual mode of reproduction. Which species is
likely to have comparatively better chances of survival – the one reproducing asexually or the
one reproducing sexually? Give reason to justify your answer. (2018)
Answer:
Difference between asexual and sexual mode of reproduction is as follows :
Asexual reproduction:
Gametes are not formed hence fertilisation does not take place.
Sexual reproduction:
Gametes are always formed and fertilisation takes place to form a zygote.

Species reproducing sexually has a better chance of survival as variations occur only during the
sexual reproduction. Variations increase the chances of survival of an individual by making them
more fit. Selection of variations by environmental factors forms the basis of evolution.

Question 31.
What happens when
(a) accidently, Planaria gets cut into many pieces-
(b) Bryophyllum leaf falls on the wet soil
(c) on maturation sporangia of Rhizopus bursts? (Delhi 2017)
Answer:
(a) When Planaria accidently gets cut into many pieces then its each piece grows into a
complete organism. This is known as regeneration.
(b) When the Bryophyllum leaf falls on the wet soil, the buds present in the notches along the
leaf margin develop into new plants. This is known as vegetative propagation.
(c) The sporangia of Rhizopus contain cells or spores that can eventually develop into new
Rhizopus individuals when it bursts on maturation.

Question 32.
Describe reproduction by spores in Rhizopus. (AI 2017)
Answer:
Fungus Rhizopus reproduces by spore formation. During the growth of Rhizopus, small
rounded, bulb-like structures develop at the top of the erect hyphae. Such structures are called
sporangia. Inside each sporangium, nucleus divides several times. Each nucleus gets
surrounded by a little amount of cytoplasm to become spore. Large number of spores are
formed inside each sporangium. After sometime sporangium bursts and spores are released in
the air. When these spores land on food or soil, under favourable conditions, they germinate
into new individuals.

Question 33.
What is vegetative propagation? State two advantages and two disadvantages of this method.
(AI 2017)
Answer:
Vegetative propagation is a type of asexual reproduction in which the plant parts other than
seeds are used as a propagule.
Advantages of vegetative propagation :

 Desirable character of the plant can be preserved through generation.

 Seedless plants can be grown through this method.

Disadvantages of vegetative propagation :

 Plants produced by this method posses less vigour and are more prone to diseases.
 Plants produced by this method show no genetic variation.

Question 34.
What is multiple fission? How does it occur in an organism? Explain briefly. Name one organism
which exhibits this type of reproduction. (Delhi 2016)
Answer:
Multiple fission refers to the process of asexual reproduction in which many individuals are
formed from a single parent. This method of reproduction occurs in unfavourable conditions.
The unicellular organism develops a protective covering called cyst, over the cell. The nucleus
of the cell divides repeatedly producing many nuclei. Later on, each nucleus is surrounded by
small amount of cytoplasm and many daughter cells are produced within the cyst.

When conditions are favourable the cyst breaks and small offspring are liberated. This type of
reproduction is seen in some protozoans, e.g., malarial parasite (Plasmodium).
Question 35.
Explain the term “regeneration” as used in relation to reproduction of organisms. Describe
briefly how regeneration is carried out in multicellular organisms like Hydra. (AI 2016)
Answer:
The process of formation of entire organism from the body parts of a fully differentiated
organism is called regeneration. It occurs by process of growth and development.
Simple animal like Hydra shows regeneration. When a small piece of Hydra breaks off it grows
into complete new Hydra.
During regeneration, the cells of cut body part of the organism divide rapidly to make a mass of
cells. The cells here move to their proper places within the mass where they have to form
different types of tissues. In this way complete organism is regenerated.

Question 36.
In the context of reproduction of species state the main difference between fission and
fragmentation. Also give one example of each. (AI 2016)
Answer:
The main differences between fission and fragmentation are as follows:

Fission Fragmentation

(i) Occurs in unicellular organisms. Occurs in multicellular organisms.

(ii) Body of organism divides by mitotic Body of the organism splits into one or more fragments

divisions into two or more daughter cells. E.g., and each fragment forms a complete organism. E.g.,

Leishmania. Spirogyra.

Question 37.
What happens when
(a) Planaria gets cut into two pieces
(b) a mature Spirogyra filament attains considerable length
(c) on maturation sporangia burst? (Foreign 2016)
Answer:
(a) When Planaria is cut into two pieces then each piece grows into a complete organism. This
is known as regeneration.
(b) When a mature Spirogyra filament attains a considerable length it breaks into small pieces
called fragments. These fragments grow into new individuals and this mode of reproduction is
called fragmentation.
(c) When a sporangium burst, large number of spores are released in the air. When these
spores land on food or soil, under favourable conditions they germinate into new individuals.
Question 38.
What is vegetative propagation? List with brief explanation three advantages of practising this
process for growing some types of plants. Select two plants from the following which are grown
by this process : Banana, Wheat, Mustard, Jasmine, Gram (Foreign 2016)
Answer:
Vegetative propagation is an asexual method of reproduction in plants. In this method, new
plants are obtained from the parts of old plants (like stems, roots and leaves), without the help
of any reproductive organs.

Advantages of vegetative propagation are as follows:

 Vegetative propagation is usually used for the propagation of those plants which produce
either very few seeds or do not produce viable seeds.
 Seedless plants can be obtained by artificial vegetative propagation.
 Grafting is a propagation method which is very useful for fruit trees and flowering bushes.
It enables to combine the most desirable characteristics of two plants.
 Plants like rose, sugarcane, cactus, etc., can be rapidly propagated through stem cuttings
as this method produces new plants from just one plant quickly without waiting for flowers
and seeds. Banana and jasmine are generally grown through vegetative propagation
method.

Question 39.
Explain budding in Hydra with the help of labelled diagrams only. (Delhi 2015)
Answer:
Refer to answer 21.

Question 40.
(a) Name the following:
(i) Thread like non-reproductive structures present in Rhizopus.
(ii) ‘Blobs’ that develop at the tips of the non- reproductive threads in Rhizopus.
(b) Explain how these structures protect themselves and what is the function of the structures
released from the ‘blobs’ in Rhizopus. (Delhi 2015)
Answer:
(a) (i)Threadlike non-reproductivestructures present in Rhizopus are called hyphae.
(ii) ‘Blobs’ developing at the tip of hyphae are called sporangia which contain spores.
(b) ‘Ihe structures called spores (released from ‘blobs’) are present in sporangia which can
develop into new Rhizopus individuals. These spores are covered with thick walls that protect
them until they come in contact with another moist surface and can begin to grow.

Question 41.
Explain any three advantages of vegetative propagation. (Foreign 2015)
Answer:
Refer to answer 19.

Question 42.
Explain the process of regeneration in Planaria. How is this process different from reproduction?
(Foreign 2015, AI 2014)
Answer:
Planaria possesses great power of regeneration. If the body of Planaria somehow gets cut into
a number of pieces, then each body piece can regenerate into a complete Planaria by growing
all the missing parts. This is shown in following figure:

During the process of reproduction, new organism is formed from the complete parent
organism. However, during fragmentation, a fragment of original parent body grows into new
individual.

Question 43.
On cutting the body of an organism into many pieces, it was observed that many of these pieces
developed as new individuals. Name the process and list two organisms in which this process
may be observed. Draw a schematic diagram to illustrate the changes that are likely to be
observed during the development of new individuals in any one of the organisms named. (Delhi
2014)
Answer:
On cutting the body of an organism into many pieces, each of these pieces develop as new
individuals. This process is known as regeneration.
Hydra and Planaria are the organism in which this process may be observed. Poliowing is the
diagram showing development of new individuals by regeneration of body parts of a parent
Hydra:

Question 44.
Draw diagrams to explain the regeneration that takes place in each of the body parts of Planaria
when its body is cut into three pieces. Name any other organism in which a similar process can
be observed. (Delhi 2014)
Answer:
Refer to answer 42.
Hydra is the organism in which regeneration is observed.

Question 45.
List any two modes of asexual reproduction in animals. Under which mode of reproduction is
vegetative propagation placed and why? List two advantages of vegetative propagation. (AI
2014)
Answer:
The two modes of asexual reproduction in animals are : (i) fission and (ii) fragmentation.
Vegetative propagation is placed under asexual mode of reproduction because in this mode
new plants are obtained from the parts of old plants (like stems, roots and leaves), without the
help of any reproductive organs. Also refer to answer 38.

Question 46.
What is vegetative propagation? List its two advantages. Select two plants raised by this
method from the list given below:
Wheat, Tomato, Rose, Pea, Gram, Corn, Banana (Foreign 2014)
Answer:
Refer to answers 38 and 26.

Question 47.
(a) Name the mode of reproduction of the following organisms and state the important feature of
each mode :
(i) Planaria
(ii) Hydra
(iii) Rhizopus
(b) We can develop new plants from the leaves of Bryophyllum. Comment.
(c) List two advantages of vegetative propagation over other modes of reproduction. (2020)
Answer:
(a) (i) Planaria – Regeneration
Regeneration of organism from its cut body parts occurs by the process of growth and
development.
Regeneration is an asexual mode of reproduction common in lower plants and animals.

(ii) Hydra – Budding

In budding, a small part of the body of the parent organism grows out as a bud which on
detaching forms a new organism.
Budding occurs in yeast, some protozoans and certain lower animals.

(iii) Rhizopus – Spores

Spores are usually produced in sporangia.
Spore formation is a common method of an asexual reproduction in bacteria and most of the
fungi.

(b) The leaves of a Bryophyllum have special type of buds in their margins. These buds may get
detached from the leaves, fall to ground and then grow to produce new Bryophyllum plants. The
buds can also drop to the ground together with the leaf and then grow to produce new plants.
(c) Advantages of vegetative propagation are :

 It is a quick method of propagation.

 The new plants produced by artificial vegetative propagation are exactly like the parent
plants.
 Many plants can be grown from one plant by vegetative propagation.

Question 48.
(a) What is fragmentation in organisms? Name a multicellular organism which reproduces by
this method.
(b) What is regeneration in organism? Describe regeneration in Planaria with the help of a
suitable diagram. (Delhi 2011)
Answer:
(a) Fragmentation is the mode of reproduction in which parent body breaks into two or more
fragments and each fragment develops into a new individual. It is a method of reproduction in
many filamentous algae, mycelial fungi and thalloid bryophytes, e.g., Spirogyra.
The given figure shows the process of fragmentation in Spirogyra:

(b) Regeneration may be defined as the ability of an organism to regenerate lost part of the
body which have been removed as by injury or autotomy. Many fully differentiated organisms
use this ability as a mode of reproduction and give rise to new individual organisms from their
body parts. It is common in Hydra, Planaria, etc.
The process of regeneration in Planaria is described in the figure given below:
Question 49.
With the help of suitable diagrams, explain the various steps of budding in Hydra. (AI 2011)
Answer:
In multicellular organisms, such as Hydra, a small protuberance arises from one side of the
body. The protuberance grows and develops adult like structure. In Hydra, it develops a
hypostome and tentacles at its free end. It develops a basal disc at the point of attachment with
the parent organism and finally gets detached to lead an independent life. Also refer to answer
21.

Question 50.
What is binary fission in organisms? With the help of suitable diagrams, describe the mode of
reproduction in Amoeba. (AI2011)
Answer:
Binary fission is the division of adult parental body into two nearly equal daughter cells. It is the
simplest and most common method of asexual reproduction found in protistan protozoans, i.e.,
Amoeba, Paramecium, etc.
Amoeba reproduces by binary fission by dividing its body into two parts. When the Amoeba cell
has reached its maximum size of growth, then first the nucleus of Amoeba lengthens and
divides into two parts. After that the cytoplasm of Amoeba divides to form two smaller Amoeba
(called daughter amoebae).
Diagrammatic representation of binary fission in Amoeba is as follows :

Question 51.
(a) What is spore formation?
(b) Draw a diagram showing spore formation in Rhizopus.
(c) List two advantages for organisms to reproduce themselves through spores. (Foreign 2011)
Answer:
(a) Spore formation is the process of formation of microscopic reproductive structures called
spores. These spores when detaches from the parent gives rise to a new individual.
Reproduction by the formation of spores is a common method of asexual reproduction in some
bacteria and most of the fungi.
(b) Following figure shows the process of spore formation in Rhizopus:

(c) Two advantages to spore producing organism are as follows:

 Spores help organism to survive harsh environmental conditions as spores are covered by
thick walls which protect them until they come in contact with moist surface and germinate.
 Spores are generally very small and light. Therefore, it ensures easy dispersal by wind,
water and animal.

Question 52.
Fertilisation is the process of
(a) transfer of male gamete to female gamete
(b) fusion of nuclei of male and female gamete
(c) adhesion of male and female reproductive organs
(d) the formation of gametes by a reproductive organ. (2020)

The growing size of the human population is a cause of concern for all people. The rate of birth
and death in a’given population will determine its size. Reproduction is the process by which
organisms increase their population. The process of sexual maturation for reproduction is
gradual and takes place while general body growth is still going on. Some degree of sexual
maturation does not necessarily mean that the mind or body is ready for sexual acts or for
having and bringing up children. Various contraceptive devices are being used by human beings
to control the size of population.
Answer:
(b) fusion of nuclei of male and female gamete

Question 53.
List two common signs of sexual maturation in boys and girls.
Answer:
(a) Two common signs of sexual maturation in boys and girls are :

 Growth of pubic hair and extra hair in the armpits.

 Development of oily skin and pimples.

Question 54.
What is the result of reckless female feticide?
Answer:
Female feticide is reducing the number of girls drastically in our country, which is also declining
male-female sex ratio.

Question 55.
Which contraceptive method changes the hormonal balance of the body?
Answer:
Chemical contraceptive method changes the hormonal balance of the body.

Question 56.
Write two factors that determine the size of a population. (2020)
Answer:
The rate of birth and death in a given population will determine the size of a population.

Question 57.
What are all organisms called which bear both the sex organs in the same individual? Give one
example of such organism. (AI 2016)
Answer:
Organisms which bear both male and female sex organs in the same individual are called
bisexual. For example, Hibiscus.

Question 58.
List two functions of ovary of human female reproductive system. (AI 2016)
Answer:
Two functions of ovary of human female are:

 production of female gametes, i.e., ova

 secretion of female hormones, i.e., estrogen and progesterone.

Question 59.
List two unisexual flowers. (Foreign 2016)
Answer:
Flowers of papaya and cucumber are unisexual.

Question 60.
Why is fertilisation not possible without pollination? (Foreign 2016)
Answer:
The process of pollination (in plants) ensures that male gametes bearing structure called pollen
comes in contact with the female reproductive structure of the plant. Once the male and female
gametes are in close vicinity, they fuse and fertilisation is accomplished. Hence, fertilisation
cannot take place without pollination.

Question 61.
Name the parts of a bisexual flower that are not directly involved in reproduction. (Foreign 2015)
Answer:
Calyx and corolla are parts of a flower that are not directly involved in reproduction.
Question 62.
No two individuals are absolutely alike in a population. Why? (Delhi 2014)
Answer:
No two individuals are absolutely alike in a population because sexual reproduction promotes
diversity of characters in the offspring by providing genetic variation.

Question 63.
Identify and write the male reproductive parts from the list of different parts of a flower given
below:
Stigma, Sepal, Anther, Petal, Ovule, Filament (Delhi 2013C)
Answer:
The male reproductive parts that are present in a flower frorti given list are:
(i) anther and (ii) filament.

Question 64.
What is the main difference between sperms and eggs of humans? Write the importance of this
difference. (AI 2014)
Answer:
The main difference between sperms and eggs of humans is that a sperm has X or Y
chromosome whereas egg has X chromosome. This helps in determination of the sex of a
person and maintaining the genetic continuity in the organisms.

Question 65.
“The chromosomal number of the sexually producing parents and their offspring is the same”.
Justify this statement. (AI 2014)
Answer:
In sexual reproduction, two gametes, male and female, combines together to form a new cell
‘zygote’. The reproductive cells or gametes contain only half the amount of DNA as compared to
the non-reproductive cells of an organism. So, when a male gamete combines with a female
gamete during sexual reproduction, then the new cell ‘zygote’ will have the normal amount of
DNA. For example, the human sperm has 23 chromosomes and the human egg has also 23
chromosomes. So when a sperm and an egg fuse together during fertilisation, then the zygote
formed will have 23 + 23 = 46 chromosomes, which is the normal number of chromosomes in
humans.

Question 66.
List two preparations shown every month by the uterus in anticipation of pregnancy in humans.
(Foreign 2014)
Answer:
The two preparations shown every month by the uterus in anticipation of pregnancy in human
are:
(i) the wall of uterus becomes thick to receive the fertilised egg and
(ii) the uterine wall is richly supplied with blood to nourish the growing embryo.

Question 67.
State one genetically different feature between sperms and eggs of humans. What is its
consequence? (Delhi 2012)
Answer:
A sperm may have X or Y chromosomes whereas egg have X chromosomes. The consequence
of this is that sperm decides the sex of the child because eggs contribute only X chromosome
while sperms contribute either X or Y chromosomes to the offspring. Therefore, if a child inherits
X chromosome from her father, will be a girl and the one that inherit Y chromosome will be a
boy.

Question 68.
State the role of placenta in the development of embryo. (AI 2012)
Answer:
Placenta is a physiological connection between an embryo and uterine wall of the mother
through which nutrients and other useful substances enter into fetus from mother’s blood and
waste products like urea and carbon dioxide are expelled into mother’s blood from fetus.

Question 69.
List the parts of human male reproductive system which contribute fluid to the semen. State two
advantages semen offers to the sperms. (Foreign 2012)
Answer:
The secretion of male accessory reproductive glands, i.e., seminal vesicles, prostate gland and
Cowper’s glands contribute fluid to the semen. The two advantages that semen offers to the
sperms are:
(i) it provides nutrition to the sperms and
(ii) it also activates the sperms and make their transport easier into the vagina of female during
sexual act.

Question 70.
Explain giving one example of each, the unisexual and the bisexual flowers. (Delhi 2011)
Answer:
(i) Unisexual flowers : These flowers contain either stamens (male reproductive part) or carpel
(female reproductive part). Example: Papaya, watermelon.
(ii) Bisexual flowers : The flower is said to be bisexual when both male and females parts, i.e.,
stamens and carpels, are present on the same flower. Example: Hibiscus, mustard.

Question 71.
Describe the role of fallopian tubes in the female reproductive system. (AI2011)
Answer:
Fallopian tubes are a pair of elongated, ciliated, muscular and tubular structures extending from
close to ovaries to uterus. It is the site of fertilisation and helps in the conduction of ovum or
zygote towards uterus by ciliary action and peristalsis.

Question 72.
Explain the terms:
(i) Implantation of zygote
(ii) Placenta (Foreign 2011)
Answer:
(i) Implantation of zygote refers to the process of attachment of the blastocyst on the inner wall
of the uterus, It occurs on 7th day after fertilisation and is controlled by estrogen and
progesterone hormones.
(ii) Refer to answer 68.
Question 73.
Define the term pollination. Differentiate between self-pollination and cross-pollination. What is
the significance of pollination? (2020)
Answer:
The process of transfer of pollen grains from anther of a flower to the stigma of the same flower
or another flower of the same species is known as pollination. The two inodes of pollination are
self pollination and cross pollination.
Differences between self pollination and cross pollination are as follows:

Character Self pollination Cross pollination

Occurs between two flowers of

Occurs within a flower or between
Occurrence two different plants of the same
two flowers of the same plant.
species.

External agents such as wind,

Usually no external agent of
Agent of pollination water, insects and birds are
pollination is required.
required.

Produced in small numbers, thus

Produced in large numbers thus,
Production of pollen grains no wastage of pollen grains
wastage of pollen grains occurs.
occurs.

Flowers are generally not Flowers are attractive with

Appearance of flowers
attractive. coloured petals.
 Commonly flowers do not produce Flowers generally produces scent
Fragrance and nectar
scent or nectar. and nectar.

Offspring produced have genetic Offspring produced may differ in

Nature of offspring produced makeup identical to the parent genetic make-up and variations

plant, no variation occurs. occur.

Pollination is important because it brings pollen grains to the female reproductive part (carpel) of
the plant that leads to fertilisation.

Question 74.
(a) What provides nutrition to human sperms? State the genetic constitution of a sperm.
(b) Mention the chromosome pair present in a zygote which determines the sex of (i) a female
child and (ii) a male child. (2020)
Answer:
(a) The secretions of seminal vesicles and prostate gland provides nutrition to the human
sperms and also make their further transport easier. The genetic constitution of a sperm can be
50% have X chromosome and 50% have Y chromosome.

(b) (i) XX – Female child

(ii) XY – Male child

Question 75.
State the basic requirement for sexual reproduction. Write the importance of such reproductions
in nature. (Delhi 2017)
Answer:
The basic requirement for sexual reproduction is involvement of both sexes, i.e., male and
female, to produce an offspring. It takes place by the combination of gametes which come from
two different parents.
The importance of sexual reproduction in nature are :
(i) Fusion of male and female gametes coming from two different and sexually distinct
individuals, exhibit diversity of characters in offspring.
(ii) Meiosis during gametogenesis provides opportunities for new combination of genes, which
leads to variation required for evolution and plays a prominent role in the origin of new species.
Variations lead to the appearance of such characters, which fit to the changing environment,
resulting in the survival of the species.

Question 76.
State the changes that take place in the uterus when:
(a) Implantation of embryo has occurred.
(b) Female gamete/egg is not fertilised. (Delhi 2017)
Answer:
(a) Implantation is the close attachment of the blastocyst (young multicellular embryo) to the
uterine wall. It is fullowed by a number of developmental changes in the thickened wall of
uterus. An intimate connection between the fetal membrane and the uterine wall called placenta
is formed. This is a disc which is embedded in the uterine wall. The placenta serves as the
nutritive, respiratory and excretory organ of the fetus.

(b) When the female gamete/egg is not fertilised, this lining is not needed any longer. So, the
lining slowly breaks and comes out through vagina as blood and mucus. This cycle takes place
every month and is known as menstrual cycle.

Question 77.
List any two steps involved in sexual reproduction and write its two advantage. (Delhi 2017)
Answer:
The two main steps involved in sexual reproduction are:

 formation of male and female gametes.

 Fusion of a male gamete with a female gamete to form a new cell called zygote by the
process of fertilisation.

The two important advantages of sexual reproduction are:

 It promotes diversity of characters in the offspring through genetic variations.

 It plays an important role in continuous evolution of better organisms that may lead to the
origin of new species.

Question 78.
List three techniques that have been developed to prevent pregnancy. Which one of these
techniques is not meant for males? How does the use of these techniques have a direct impact
on the health and prosperity of a family? (AI 2017)
Answer:
Methods developed to prevent pregnancy are:

 barrier method, i.e., use of condoms, diaphragm, etc.

 chemical method, i.e., use of oral pills or vaginal pills.
 surgical method, i.e., vasectomy and tubectomy. Out of these methods, chemical method
is not meant for males.

Use of these techniques help to keep control over number of children in a family, which directly
effects prosperity of a family. One of the most common reason for deterioralion of women’s
health is frequent conception and child bearing. Controlled childbirth will directly affect women
health and this will indirectly affect the prosperity of family and nation.

Question 79.
How do organisms, whether reproduced asexually or sexually maintain a constant chromosome
number through several generations? Explain with the help of suitable example. (Delhi 2016)
Answer:
In organisms reproducing asexually, only single parent is involved in reproduction. Therefore,
amount of DNA remains same from parent to offspring. For example in Amoeba, whole
organism divides into two daughter individuals by binary fission. Therefore, amount of DNA
remain constant.

In organisms reproducing sexually, reproduction take place with the help of formation of haploid
gametes. Gametes are special type of cells called reproductive cells which contain only half the
amount of DNA as compared to the normal body cells of an organism. So, when a male gamete
combines with a female gamete during sexual reproduction, then the new cell ‘zygote’ will have
the normal amount of DNA. For example, the human sperm has 23 chromosomes and the
human egg (or ovum) has also 23 chromosomes. So, when a sperm and an egg fuse together
during fertilisation, then the zygote formed will have 23 + 23 = 46 chromosomes, which is the
normal number of chromosomes.

Question 80.
Name the parts A, B and C shown in the following diagram and state one function of each.
(Delhi 2016)

Answer:
In the given figure, part A is anther, part B is style and part C is ovule.
Anther (A) is a part of male reproductive organ of flower called stamen. Large number of pollen
grains are formed inside anther. Style (B) and ovule (C) are parts of female reproductive organ
of flower called carpel / pistil.

Style is a long conducting tube which gives the passage to pollen tube carrying male gametes
so that it reaches ovary which contains one or more ovules. Ovules contain female gamete or
egg. On fertilisation ovary converts into fruit and ovules give rise to seeds.

Question 81.
Suggest three contraceptive methods to control the size of human population which is essential
for the health and prosperity of a country. State the basic principle involved in each. (Delhi
2016)
Answer:
Three contraceptive methods which can help to control human population are:
(i) Condom : It is a mechanical barrier which does not allow sperms and ovum to meet, hence
prevents fertilisation. Condoms are made of thin rubber/latex sheath used to cover the penis in
the male and vagina/cervix in female just before coitus (intercourse) so that the ejaculated
semen is not released in the female reproductive tract.

(ii) Intrauterine devices (IUDs): These are devices inserted by doctors or expert nurses in the
uterus through vagina. These are presently available as non-medicated IUDs, copper releasing
IUDs (CuT, etc.) and hormone releasing IUDs. They increase phagocytosis of sperms within
uterus and suppress sperm motility and its fertilising capacity. They also make uterus unsuitable
for implantation and cervix hostile to sperms.
(iii) Oral pills : These pills contain progesterone alone or a combination of progestogen and
estrogen. They inhibit ovulation and make uterus unsuitable for implantation, hence prevent
fertilisation.

Question 82.
What are the functions of testes in the human male reproductive system? Why are these
located outside the abdominal cavity? Who is responsible for bringing about changes in
appearance seen in boys at the time of puberty? (Delhi 2016)
Answer:
Testes, in human males, are the primary reproductive organs. They are the site of sperm
formation. The testes also produce male sex hormone testosterone. Testes are located outside
the abdominal cavity because sperm formation requires a lower temperature than normal body
temperature. The temperature of the testes in the scrotum is about 2-2.5°C lower than normal
body temperature. This temperature is ideal for sperm formation and development. Hormone
testosterone brings about the development of secondary sexual characters during puberty in
boys like growth of facial hair, deepening of voice, growth of scrotum and penis, accumulation of
muscle mass, etc., and also regulates formation of sperms.

Question 83.
What is meant by pollination? Name and differentiate between the two modes of pollination in
flowering plants. (Delhi 2016)
Answer:
Refer to answer 73.

Question 84.
(a) List two reasons for the appearance of variations among the progeny formed by sexual
reproduction.

(i) Name the part marked A in the diagram.

(ii) How does A reaches part B?
(iii) State the importance of the part C.
(iv) What happens to the part marked D after fertilisation is over? (AI 2016)
Answer:
(a) Variations arise in sexually reproducing organisms on account of the following:
(i) Genetic variations occur of because DNA copying mechanism is not absolutely accurate.
(ii) Creation of new combinations of genetic variations because variations from two individuals
combine during fusion of gametes.
(b) (i) A is pollen grain.
(ii) Part B is stigma. It is the part of pistil (female reproductive organ) that receives pollen grains.
Pollen grains reach stigma through various agencies like wind, water, insect, etc.
(iii) Pollen tube (C) carries male gametes to the ovule present in ovary. Male gametes fuse with
egg and secondary nucleus to give rise to zygote and endosperm.
(iv) Female gamete (D) fuses with male gamete and converts to embryo after fertilisation.

Question 85.
What is pollination? List its two types and write a distinguishing feature between the two.
(Foreign 2016)
Answer:
Refer to answer 73.

Question 86.
What is sexual reproduction? List its four significances. (Foreign 2016)
Answer:
Sexual reproduction is the process of production of offspringby the fusion of male and female
gametes. Here, haploid gametes fuse to form diploid zygote which develop into a mature
organism.
Significance of sexual reproduction are as follows:

 Sexual reproduction gives rise to genetic variations because of genetic recombination that
takes place during fusion of gametes.
 Progenies arising through sexual reproduction sometimes show better combination of
traits and get better adapted to their surroundings.
 Genetic recombination, interaction, etc., during sexual reproduction provide vigour and
vitality to the offspring.
 Variations in genes play an important role in evolution.

Question 87.
Name the reproductive parts of an angiosperm. Where are these parts located? Explain in brief
the structure of its female reproductive parts. (Foreign 2016)
Answer:
The reproductive parts of an angiosperm are stamen (male reproductive part) and carpel/pistil
(female reproductive part). These are located in the flowers of an angiospermic plant.
The given diagram shows the structure of female reproductive part of a flower:

A Carpel is made of three parts: stigma, style and ovary. The top part of carpel is called stigma.
Stigma is for receiving the pollen grains during pollination. Stigma is sticky so that pollen can
stick to it. The middle part of carpel is called style. Style is a tube which connects stigma to the
ovary. The swollen part at the bottom of a carpel is called ovary. The ovary contains ovules.
Ovules contain the female gametes or female sex cells (egg) of the plant. There are usually
many ovules in the ovary. Each ovule contains only one female gamete of the plant.

Question 88.
(a) Mention the role of the following organs of human male reproductive system.
(i) Testes (ii) Scrotum (iii) Vas deferens
(iv) Prostate gland
(b) What are the two roles of testosterone? (Foreign 2016)
Answer:
(a) (i) Testes : The two testes in male are the sites where male gametes, i.e., sperms are
formed. Testes also produce the male sex hormone called testosterone.
(ii) Scrotum : The scrotum is a pouch of skin that lie outside abdominal cavity. The two testes lie
in respective scrotal sacs. The scrotum acts as a thermoregulator and provides an optimal
temperature for the formation of sperms.
(iii) Vas deferens : This is a straight tube, about 40 cm long, which carries the sperms to the
seminal vesicles, where mucus and a watery alkaline fluid containing fructose, mix with the
sperms.
(iv) Prostate gland : It is a single large gland that surrounds the urethra and produces a milky,
slightly acidic secretion. Secretion of prostate gland nourishes and activates the sperm to swim.

(b) Two roles of testosterone are:

(i) It plays a key role in development of male secondary sex organs such as prostate, etc.
(ii) It promotes the secondary sexual character-istics in males such as increased muscle and
bone mass, growth of body hair, etc.

Question 89.
List any four methods of contraception used by humans. How does their use have a direct effect
on the health and prosperity of a family? (Delhi 2015, 2014)
Answer:
The four methods of birth control which deliberately prevent fertilisation in humans are:

 Barrier method- These are physical devices to prevent the entry of sperm in the female,
e.g., condoms.
 Chemical method – It involves the use of oral pills that check ovulation. These are mainly
hormonal preparations and contain estrogen and progesterone.
 Intrauterine contraceptive device-These devices are implemented into uterus, e.g., copper
– T, to prevent fertilisation.
 Surgical methods : These methods involves removal of a small jJortion of vas deferens in
males or fallopian tube in females to prevent fertilisation. Contraception prevents frequent
pregnancies and sexually transmitted diseases thus supports good health and prosperity
of a family.

Question 90.
What are sexually transmitted diseases? List two examples each of diseases caused due to
(i) bacterial infection and (ii) viral infection. Which device or devices may be used to prevent the
spread of such diseases? (Delhi 2015)
Answer:
The diseases that are spread by sexual contact with an infected person are called sexually
transmitted disease (STDs).
(i) Bacterial infection causes gonorrhoea, syphilis.
(ii) Viral infection causes AIDS, genital herpes. STDs can be prevented by using male and
female condoms.

Question 91.
List six specific characteristics of sexual reproduction. (AI 2015)
Answer:
Six specific characteristics of sexual reproduction are as follows:

 Two different sexes, i.e., male and female are involved in this process.
 Sexual reproduction involves formation of special sex cells called gametes.
 Fusion of gametes or fertilisation takes place in the body of female (internal fertilisation) or
outside (external fertilisation).
 Offspring inherit traits from both parents (heredity) and also show some new traits of their
own (variation), hence they are not clones of the parents.
 Variations in sexually reproducing organisms arises on account of crossing over during
meiotic division during gamete formation.
 It plays a prominent role in origin of new species as it leads to variations which accumulate
over a period of time and get carried to successive generations.

Question 92.
List four points of significance of reproductive health in a society. Name any two areas related to
reproductive health which have improved over the past 50 years in our country. (AI 2015)
Answer:
The general awareness regarding reproductive health in a society is significant as :

 Maintenance of personal hygiene among youngsters and proper knowledge of their

reproductive parts helps them adjust with the physical changes and cope with emotional
disturbances.
 Reproductively healthy society must be free from the curse of child marriage which begets
many complications at the level of individual and society both.
 Proper care of expecting mothers, monitoring their health after child birth and care of new
born help in building a healthy society.
 Married couples aware of contraceptive methods lead a better married life as they are
capable of avoiding unwanted pregnancies and have negligible chances of contracting
sexually transmitted diseases.

In past 50 years, various areas related to reproductive health have been launched which have
improved the reproductive health of our society in following ways: Two of them are :
(i) reduced mortality rate of mother and infant
(ii) birth control due to easily available contraceptive and reduced STDs cases.

Question 93.
Draw longitudinal section of a bisexual flower and label the following parts on it.
(i) Anther
(ii) Ovary
(iii) Stigma
(iv) Style (Foreign 2015)
Answer:
Longitudinal section of a bisexual flower is as follows:

Question 94.
What is placenta? Explain its function in humans. (Foreign 2015, AI 2014)
Answer:
Placenta is an intimate connection between fetus and uterine wall of the mother to exchange the
materials. It is a disc shaped structure embedded in the uterine wall. It contains villi on embryo’s
side and blood spaces towards mothers side. Blood spaces surround villi.

Placenta performs the following functions:

 All nutritive elements from maternal blood pass into the fetus through it.
 Placental helps in respiration, i.e., supply of oxygen and removal of CO2 from fetus to
maternal blood.
 Fetal excretory products diffuse out into maternal blood through placenta and are excreted
by mother.
 Placenta also secretes hormone.

Question 95.
Write one main difference between asexual and sexual mode of reproduction. Which species is
likely to have comparatively better chances of survival – the one reproducing asexually or the
one reproducing sexually? Justify your answer. (Foreign 2015, AI 2014)
Answer:
Difference between asexual and sexual mode of reproduction is as follows :
Asexual reproduction :
Gametes are not formed hence fertilisation does not take place.

Sexual reproduction :
Gametes are always formed and fertilisation takes place to form a zygote.

Species reproducing sexually have a better chance of survival as variation occurs only during
the sexual reproduction. Variations are necessary for evolution and to increase chances of
survival in changed environmental conditions.

Question 96.
Why is DNA copying an essential part of the process of reproduction? What are the advantages
of sexual reproduction over asexual reproduction? (Foreign 2015)
Answer:
DNA copying is an essential part of the process of reproduction as it results in passing of nearly
same genetic information from parents to the offsprings. DNA replication also ensures that
same number of chromosomes are passed from parents to offspring.

Advantages of sexual reproduction over asexual reproduction is that sexual reproduction

provides variations which is a major factor for evolution that helps in survival of species in
changing environment.

Question 97.
Draw a diagram of the longitudinal section of a flower exhibiting germination of pollen on stigma
and label (i) ovary (ii) male germ cell,
(iii) female germ cell and (iv) ovule on it. (Foreign 2015)
Answer:
The diagram of the longitudinal section of flower is as follows:

Question 98.
Write names of those parts of a flower which serve the same function as the following do in the
animals
(i) testes
(ii) sperm
(iii) ovary
(iv) egg. (Delhi 2014)
Answer:
The parts of a flower which serve the same function as following do in the animals are
(i) testes – anther of stamen
(ii) sperm – pollen
(iii) ovary – ovary of pistil
(iv) egg – female germ cell present in ovule.

Question 99.
List four methods of contraception used by humans.
Justify the following statement.
“The use of contraceptive methods has a direct effect on the health and prosperity of a family.”
(AI 2014)
Answer:
Refer to answer 89.

Question 100.
Describe in brief the function of the various parts of the female reproductive part of a bisexual
flower. (Foreign 2014)
Answer:
Refer to answer 87.

Question 101.
On the notice board of ultrasound clinics it is generally stated. “Here prenatal sex determination
and disclosure of sex (boy or girl before birth) of fetus is not done. It is prohibited and
punishable under law.”
(a) List two advantages of imposing ban on prenatal sex determination.
(b) What can students do to educate the society about the following?
(i) The ill-effects of indiscriminate female feticide.
(ii) Adopting small family norms. (Foreign 2014)
Answer:
(a) The two advantages of imposing ban on prenatal sex determination are
(i) check on female feticide
(ii) improving sex ratio in the country.

(b) Students should educate the society as that

(i) female feticide is reducing the number of girls drastically in some societies. For a healthy
society, the male-female sex ratio must be maintained at almost the same level. Due to reckless
female feticide, the male-female child sex ratio is declining at an alarming rate in some sections
of our society.

(ii) Children in a small family can be provided with all the resources from education, good
amenities like food, clothing and healthy life style. As the family grows larger, the resources
should be shared with increased number of member. Having fewer children also keeps the
mother in good health.

Question 102.
Name the two reproductive parts of a bisexual flower which contain the germ cells. State the
location and function of its female reproductive part. (Foreign 2014)
Answer:
The two reproductive parts of a bisexual flower which contain the germ cells are carpel (female
reproductive part) and stamen (male reproductive part). Carpel is situated in the centre of the
flower as a flask-shaped structure. A carpel is made up of three parts-stigma, style and ovary.
The distal part of a carpel is called stigma. Stigma is responsible for receiving pollen during
pollination. Style is an elongated tubular structure which connects stigma with ovary. The basal
swollen part of carpel is ovary. Ovary bears several ovules. After fertilisation ovules form seeds
and ovary forms the fruit.

Question 103.
Write two examples each of sexually transmitted diseases causes by (i) virus, (ii) bacteria.
Explain how the transmission of such diseases be prevented? (Delhi 2013)
Answer:
The infectious (communicable) diseases, which are spread from an infected person to a healthy
person by sexual contact, are called sexually transmitted diseases.
Sexually transmitted diseases caused by virus are : AIDS (Acquired Immunodeficiency
Syndrome) and genital warts while caused by bacteria are gonorrhoea and syphilis.

Preventive measures for these diseases are:

 educating people in high risk groups.

 mutually faithful monogamous relationship.
 avoiding prostitution, multipartner sex and homosexuality.
 using condoms, etc.

Question 104.
Explain the meaning of sexually transmitted diseases (STDs). Give two examples of STDs
each, caused due to (i) bacterial infection and (ii) viral infection. State in brief how the spread of
such diseases may be prevented. (Delhi 2012)
Answer:
Refer to answer 103.

Question 105.
List and explain in brief three methods of contraception. (AI 2012)
Answer:
Refer to answer 81.

Question 106.
What is AIDS? Which microbe is responsible for AIDS infection? State one mode of
transmission of this disease. Explain in brief one measure for prevention of AIDS. (Foreign
2012)
Answer:
AIDS (Acquired Immunodeficiency Syndrome), is an infectious viral disease which weakens the
immune system of human body and generally leads to death. It is caused by a retrovirus called
HIV (Human Immunodeficiency Virus). AIDS can be transmitted by having sexual contact with
an infected person.
Use of condoms which are physical barriers can reduce the risk of a sexual exposure to HIV.

Question 107.
(a) List two sexually transmitted diseases in each of the following cases:
(i) Bacterial infections
(ii) Viral infections
(b) How may the spread of such diseases be prevented? . (Delhi 2011)
Answer:
Refer to answer 103.

Question 108.
What does HIV stands for? Is AIDS an infectious disease? List any four modes of spreading
AIDS. (AI 2011)
Answer:
HIV stands for Human Immunodeficiency Virus. Yes, AIDS is an infectious disease. It is
transmitted sexually or through exposure to contaminated blood.
Four modes of spreading AIDS are :

 unprotected sex with an infected partner

 use of contaminated needle and syringes
 use of contaminated razors for shaving
 transfusion of infected blood or blood products.

Question 109.
Expand AIDS. List any four methods of prevention (control) of AIDS. (Foreign 2011)
Answer:
AIDS is expanded as Acquired Immuno-deficiency Syndrome.
Four methods of prevention or control of AIDS are :

 use of sterilised needles and syringes for injecting drugs or vaccine

 to avoid sex with multiple partners
 use of condoms during intercourse
 avoid use of contaminated razor in barber shop.

Question 110.
(a) List three different categories of contraceptive methods.
(b) Why has Government of India prohibited prenatal sex determination by law? State its
benefits in the long run.
(c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections
caused due to unsafe sex. (2020)
Answer:
(a) Three different categories of contraceptive methods are :
(i) Barrier methods, i.e., use of condoms, etc.
(ii) Chemical methods, i.e., use of oral pills or vaginal pills.
(iii) Surgical methods, i.e., vasectomy and tubectomy.

(b) Prenatal sex determination was banned in India in 1994. This was done to prevent sex
selective abortion. It is being used to kill the normal female fetus. This killing of the unborn girl
child is called female feticide which is reducing the number of girls drastically in some societies
of our country. Due to reckless female feticide, male-female sex ratio is declining at an alarming
rate. Its benefit in the long run is that the female-male ratio could be maintained for a healthy
society.

(c) Bacterial diseases due to unsafe sex are gonorrhoea, syphilis.

Viral diseases due to unsafe sex are AIDS, genital herpes.

Question 111.
(a) In the female reproductive system of human beings, state the functions of:
(i) Ovary
(ii) Oviduct.
(b) Mention the changes which the uterus undergoes, when
(i) it has to receive a zygote.
(ii) no fertilisation takes place.
(c) State the functions of placenta. (2020)
Answer:
(a) (i) Tire ovaries in female are primary sex organs (or female gonads) which perform the dual
function – production of female gametes (eggs or ova) and secretion of female sex hormones
(estrogen and progesterone).
(ii) Oviducts or fallopian tube are paired tubes originating near to the ovaries of their respective
sides and extend upto uterus. The terminal part of fallopian tube is funnel-shaped with finger-
like projections called fimbriae lying near ovary. Fimbriae pick up the ovum released from ovary
and push it into fallopian tube. Fertilisation also takes place in the oviduct.

(b) (i) As the ovary releases one egg every month, the uterus also prepares itself, every month
to receive fertilised egg by making its lining thick and spongy to nourish the zygote if fertilisation
takes place.
(ii) When the female gamete/egg is not fertilised, this lining is not needed any longer. So, the
lining slowly breaks and comes out through vagina as blood and mucus through menstrual cycle
that takes place every month.

(c) Placenta performs the following functions :

 All nutritive elements from maternal blood pass into the fetus through it.
 Placenta helps in respiration i.e., supply of oxygen and removal of CO2 from fetus to
maternal blood.
 Fetal excretory products diffuse out into maternal blood through placenta and are excreted
by mother.
 Placenta also secretes hormone.

Question 112.
(a) Draw a diagram showing germination of pollen on stigma of a flower and mark on it the
following organs/parts:
(i) Pollen grain
(ii) Pollen tube
(iii) Stigma
(iv) Female germ cell
(b) State the significance of pollen tube.
(c) Name the parts of flower that develop after fertilisation into:
(i) Seed
(ii) Fruit. (2020)
Answer:
(a) Diagram showing germination of pollen on stigma of a flower is:

(b) The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain at
stigma to the ovules at the base of the carpel for the process of fertilisation.

(c) After fertilisation,

(i) ovule develops into seed and
(ii) ovary develops into fruit.

Question 113.
Draw a neat diagram showing fertilisation in a flower and label (a) pollen tube (b) Male germ cell
and (c) Female germ cell on it. Explain the process of fertilisation in a flower. What happens to
the (i) ovary and (ii) ovule after fertilisation? (2020)
Answer:
Diagram showing fertilisation in a flower:

Fertilisation, in plants, occurs when the male gamete present in pollen grain fuses with the
female gamete (or egg) present in ovule. When a pollen grain falls on the stigma of the carpel, it
bursts open and grows a pollen tube downwards through the style towards the female gamete in
the ovary. Male gametes move down the pollen tube. The pollen tube enters the ovule in the
ovary. The tip of pollen tube bursts and male gametes comes out of pollen tube. In ovary, the
male gamete of pollen combines with the female gamete or egg present in ovule to form a
fertilised egg.

After fertilisation,
(i) ovule develops into seed
(ii) ovary develops into fruit.

Question 114.
(a) What is puberty?
(b) Describe in brief the functions of the following parts in the human male reproductive system.
(i) Testes
(ii) Seminal vesicle
(iii) Vas deferens
(iv) Urethra
(c) Why are testes located outside the abdominal cavity?
(d) State how sperms move towards the female germ cell. (2020)
Answer:
(a) The age at which the sex hormones begin to be produced and the boy and girl becomes
sexually mature, i.e., able to reproduce is called puberty.

(b) (i) Testes : The two testes in male are the sites where male gametes, i.e., sperms are
formed. Testes also produce the male sex hormone called testosterone.
(ii) Seminal vesicles are one pair of sac-like structures near the base of bladder. Seminal fluid is
a watery alkaline fluid that contains nutrients (fructose) which serve as a source of energy for
the sperm. Each seminal vesicle releases its contents into the ejaculatory duct during
ejaculation.
(iii) Vas deferens : This is a straight tube, about 40 cm long, which carries the sperms to the
seminal vesicles, where mucus and a watery alkaline fluid containing fructose, mix with the
sperms.
(iv) Urethra : It is a long tube that arises from urinary bladder. Urethra carries urine from the
bladder as well as sperms from the vas deferens, through the penis.

(c) Testes are located outside the abdominal cavity because sperm formation requires a lower
temperature than normal body temperature. The temperature of the testes in the scrotum is
about 2-2.5°C lower than normal body temperature. This temperature is ideal for sperm
formation and development.

(d) The sperms present in the testes of man are introduced into the vagina of the woman
through penis during copulation. Millions of sperms are released into the vagina at one time.
The sperms are highly active and mobile. They travel from here upward through the uterus at
the top of fallopian tube within five minutes
41) (a) Identify the given diagram. Name the parts 1 to 5.

(b) What is contraception? List three advantages of adopting contraceptive measures. (Delhi
2019)
Answer:
(a) The given diagram is the sectional view of human female reproductive system.
The labelled parts are:
1. Funnel of fallopian tube or oviduct
2. Ovary
3. Uterus or womb
4. Cervix
5. Vagina

(b) Contraception is the avoidance of pregnancy. There are several methods of contraception
such as:

 Barrier methods (condoms, diaphragm, etc.)

 Chemical methods (spermicide creams and jellies)
 Intrauterine Contraceptive Devices (IUCDs) (Lippes loop, CuT, etc.)
 Natural methods (rhythm method, coitus interruptus)

Surgical methods (vasectomy, tubectomy) Three advantages of adopting contraceptive methods

are:

 They prevent frequent or unwanted pregnancies.

 They prevent the transfer of sexually transmitted diseases (STDs).
 They help to regulate the population growth.

42) (a) Name the organ that produces sperms as well as secretes a hormone in human males.
Name the hormone it secretes and write its functions.
(b) Name the part of the human female reproductive system where fertilisation occurs.
(c) Explain how the developing embryo gets nourishment inside the mother’s body. (Delhi 2017)
Answer:
(a) Refer to answers 88 (a)(i) and (b).
(b) In human female the fertilisation occurs in the oviducts or Fallopian tube.
(c) The developing embryo gets nourishment from the mother’s blood with the help of a special
tissue called placenta. This is a disc like structure embedded in uterine wall. It contains villi that
provides a large surface area to pass glucose and oxygen from mother to embryo. Placenta
links the embryo to the mother through umbilical cord

43) What is menstruation? Why does it occur? (Foreign 2016)

Answer:
(b) Menstruation is the cyclic discharge of blood along with endometrial lining of the uterus and
unfertilised egg in women. It last for 3-5 days. After the release of egg in the females, the
uterine lining becomes thickened for the implantation of fertilised egg or zygote. In the absence
of fertilisation, the egg along with endometrial lining is expelled out of the body in the form of
menstruation.

44) (a) Give one example each of unisexual and bisexual flower.
(b) Mention the changes a flower undergoes after fertilisation.
(c) How does the amount of DNA remain constant though each new generation is a combination
of DNA copies of two individuals. (Delhi 2014)
Answer:
(a) Unisexual flowers bear organs of only one sex, i.e., either stamen or pistil, e.g., papaya.
Bisexual flowers contain both stamen and pistil, e.g., Hibiscus.

(b) After fertilisation, the fertilised egg (or zygote) divides several times to form an embryo within
the ovule. The ovule develops a tough coat around it and is gradually converted into a seed.
The ovary of flower develops and becomes a fruit (with seeds inside it). The other parts of
flower like sepals, petals, stamens, stigma and style dry up and fall off. Only the ovary is left
behind. So, at the place on plant vyhere we had a flower originally, we now have a fruit (which is
the ovary of the flower containing seeds). A fruit protects the seeds.

(c) The amount of DNA remain constant in each new generation because of formation of haploid
gametes. Gametes are special type of cells called reproductive cells which contain only half the
amount of DNA as compared to the normal body cells of an organism. So, when a male gamete
combines with a female gamete during sexual reproduction, then the new cell ‘zygote’ will have
the normal amount of DNA. For example, the human sperm has 23 chromosomes and the
human egg (or ovum) has also 23 chromosomes. So, when a sperm and an egg fuse together
during fertilisation, then the zygote formed will have 23 + 23 = 46 chromosomes, which is the
normal number of chromosomes.

45) List in tabular form the two differences between asexual and sexual mode of reproduction.
Name and explain with the help of labelled diagram the process by which Hydra reproduces
asexually. (Foreign 2014, Delhi 2013C)
Answer:
Differences between asexual and sexual forms of reproduction are follows :

Characters Asexual reproduction Sexual reproduction

 The process involves only one cell This process involves two cells or

(i) Number of parents or one parent, so is called gametes belonging to different

uniparental reproduction. parents, so is generally biparental.

The whole body of the parent acts

The reproductive unit is gamete,
(ii) Reproductive unit as reproductive unit or it can be in
which is unicellular and haploid.
a single cell or a bud.

The offsprings are genetically

(iii) Nature of offspring The offsprings differ from parents.
similar to parents.