FULL PORTION -3

answer key
CLASS XII

BIOLOGY (044)

Maximum Marks: 70 Time: 3 hours

General Instructions:
(i) All questions are compulsory.
(ii) The question paper has five sections and 33 questions. All questions are compulsory.
(iii) Section–A has 16 questions of 1 mark each; Section–B has 5 questions of 2 marks
each; Section– C has 7 questions of 3 marks each; Section– D has 2 case-based
questions of 4 marks each; and Section–E has 3 questions of 5 marks each.
(iv) There is no overall choice. However, internal choices have been provided in some
questions. A student has to attempt only one of the alternatives in such questions.
Wherever necessary, neat and properly labeled diagrams should be drawn.
Section A
1. Which connective tissue surrounds the testis?
(a) Fibrous tissue
(b) Spongy connective tissue
(c) Tunica albuginea
(d) None of them
ANSWER
(c) Tunica albuginea
2. What is the reason for the popularity of the barrier method of family planning?
(a) The absence of side effect
(b) Comparatively more reliable
(c) Protection from sexually transmitted diseases.
(d) Both a and b
ANSWER
(d) Both a and b
3. Eukaryotic cells have a nucleus that is considerably larger than the DNA molecule. How is the
DNA accommodated here?
(a) super-coiling in nucleosomes
(b) DNase digestion
(c) through the elimination of repetitive DNA
(d) deletion of non-essential genes
ANSWER
(a) super-coiling in nucleosomes
4. Which of the following is not a source of variation in a population?
(a) Inherited genetic differences
(b) Differences due to health
(c) Differences due to age
(d) None of the above
ANSWER
(b) None of the above.
5. What type of barrier does saliva in the mouth and tears from the eyes belong to under innate
immunity?
(a) Cytokine barriers
(b) Cellular barriers
(c) Physiological barriers
(d) Physical barriers
ANSWER
(c) Physiological barriers
6. Patients can be diagnosed by observing their symptoms. Which group of symptoms indicate
pneumonia?
(a) Difficulty in respiration, fever, chills, cough and headache
(b) Constipation, abdominal pain, cramps and blood clots
(c) Nasal congestion and discharge, cough, sore throat and headache.
(d) High fever, weakness, stomach pain, loss of appetite and constipation.
Answer
(a) Difficulty in respiration, fever, chills, cough and headache
7. What is a free-living nitrogen-fixing cyanobacterium that forms a symbiotic association with
the water fern Azolla?
(a) Anabaena
(b) Tolypothrix
(c) Chlorella
(d) Nostoc
ANSWER
(a) Anabaena
8. Suppose an electrical current has moved DNA fragments through a gel. What does the band on
this gel that is furthest from the top (that is, from where the DNA fragments were added)
represent?
(a) shortest fragments of DNA
(b) longest fragments of DNA
(c) restriction enzyme used to cut the DNA into fragments
(d) ligase used to bind the DNA fragments together
ANSWER
(a) shortest fragments of DNA
9. In which of the following cases are an organism and its kind of association a matching pair?
(a) Shark and suckerfish – Commensalism
(b) Algae and fungi in lichens – Mutualism
(c) Orchids growing on trees – Parasitism
(d) Cuscuta (dodder) growing on other – flowering plants – Epiphytism
ANSWER
(b) Algae and fungi in lichens – Mutualism
10. Species whose populations have been severely depleted and their ultimate survival is
uncertain are known as?
(a) Threatened species
(b) Endangered species
(c) Vulnerable species
(d) Rare species
ANSWER
(a) Endangered species
11. Trophic levels are formed by :
(a) plants
(b) animals
(c) organisms linked in food chain
(d) carnivores
Answer
C .organisms linked in food chain
12. What is the primary reason for the decrease in species diversity in tropical countries?
(a) Urbanisation
(b) Pollution
(c) Deforestation
(d) Soil erosion
ANSWER
(c) Deforestation
Question No. 13 to 16 consist of two statements – Assertion (A) and Reason (R). Answer these
questions selecting the appropriate option given below:
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true and R is not the correct explanation of A.
C. A is true but R is false.
D. A is False but R is true.
13. Assertion : Chasmogamous flowers require pollinating agents.
Reason : Cleistogamous flowers do not expose their sex organs’
Answer:b
14. Assertion : Cross of F1 individual with recessive homozygous parent is test cross.
Reason : No recessive individual are obtained in the monohybrid test cross progeny.
Answer(c)
15. Assertion : Transgenic plant is a product of plant tissue culture.
Reason : An organism that contains and expresses a transgenic organism.
AnswerAnswer: (b)
16. Assertion : Leaf butterfly and stick insect show mimicry to dodge their enemies.
Reason : Mimicry is a method to acquire body colour blending with the surroundings
Answer: (a) Leaf butterfly is green in colour and stick insect also mimics in order to escape from
the enemies and also to catch prey.
Section B
17. Observe the diagram given below and name the parts labelled A, B,C,D.

Answer:

A- Endometrium, B- Ovary , C- Isthmus of fallopian tube, D-Ampulla of fallopian tube

(½+ ½+½+ ½)
18. In Snapdragon, a cross between true -breeding white-flowered (RR) plants showed a progeny
of plants with all pink flowers.
i)The appearance of pink flowers is not known as blending. Why?
Answer:
It is not a case of blending. In this case, R gene was not completely dominant over r gene and
this made genotype Rr to distinguish as pink. ½+ ½
(ii) What is this phenomenon known as?
Answer:
Incomplete dominance. 1
19.Name an allergen and write the response of human body when exposed to it .
Ans.The allergen can be pollen grains, spores or dust particles. ½+ ½
When the allergens are inhaled or enter body system, they stimulate body to produce IgE
antibodies and trriger an anti-allergic reaction. /The chemical such as histamine and serotonin are
released from mast cells, in respons to allergen, thereby causing dilation of blood vessels. The
other symptoms of allergy, i.e. sneezing, watery eyes, running nose, etc ½+ ½
20. (i) Illustrate the recognition sequence of EcoRI and mention what such sequences are called?
(ii) How does restriction endonuclease act on a DNA molecule?

Ans.(/’) Recognition sequence of EcoRl

5′- G A A T T C -3′
3′- C T T A A G -3′
These sequences are called palindromic nucleotide sequences. 1
(ii) Restriction endonuclease acts on specified length of a DNA and binds to the DNA at the
specific recognition sequence. It cuts both the double strands of DNA, at the sugar phosphate
backbones, a little away from the centre of palindromic sites in between the specific sequence or
points.1
21.Why the pyramid of energy is always upright? Explain.
Answer:
Pyramid of energy is always upright because when energy flows from a particular trophic level
to the next trophic level, some energy is always lost as heat at each step.1
Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a
given time.1
Or
Identify the type of given ecological pyramid and give one example each of pyramid of number
and pyramid of biomass in such cases.
a)
fish
Phytoplankto
n

b)
Primary consumer
Primary
producer

Answer:
a)Given ecological pyramid represents the inverted pyramid of biomass /wherein small standing
crop of phytoplanktons supports large standing crop of zooplankton. 1
b)pyramid of biomass ( standing crop)
Pyramid of number is inverted in tree ecosystem and that of biomass in pond ecosystem. 1
Section C
22.Give the names and functions of the hormones involved in the process of spermatogenesis.
Write the names of the endocrine glands from where they are released.
Answer:
 Hormone EndocrIne gland Functions

Stimulates Sertoli cells to secrete

(1) FSH Antenor pituitary some factors which help in

spermatogenesis.

Stimulates Leydig’s cells of testes

to secrete androgens (especially

(2) ICSH/LH -do-
testosterone) which regulate

spermatogenesis.

(1+1)

23. Discuss the role of predators in an ecosystem.

Answer:
Predators are of great importance as they play the following important roles in an ecosystem:

1. They act as ‘conduits’ for energy transfer to higher trophic levels.

2. They keep the prey population under control, which otherwise can reach very high
population density and cause an imbalance in the ecosystem,
3. They help in maintaining species diversity in a community by reducing the
intensity of competition among the competing prey species. (1+1+1)

24. Mention the three steps involved in each cycle of Polymerase Chain Reaction (PCR). How is
repeated amplification of DNA made possible using PCR?
Ans. (i) A-Denaturation of the double stranded DNA.
(ii) B-Annealing (iii) C-Extension . ½+ ½+½

Importance in PCR
It extends the primers using the nucleotides provided in the reaction medium and the genomic
DNA as the template. /Taq polymerase is thermostable and withstands the high temperature used
in denaturation process.
Repeated amplification of DNA in PCR is made possible by using thermostable DNA
polymerase, /which remain active during high temperature. ½+ ½+½

25.
(i) Explain adaptive radiation with the help of suitable example.
(ii)Give an example where more than one adaptive radiation have occurred in an isolated
geographical area.
Answer:
(i) The process of evolution of different species in a given geographical area starting from a point
and literally radiating to other areas or habitat is called adaptive radiation, /e.g. alterations in
beaks of finches on Galapagos Islands.½+ ½

(ii) An example where more than one adaptive radiation have occur in an isolated geographical
area is Australian marsupials,/ where a number of different marsupials evolved from an ancestral
stock but within the isolated Australian island and all of them got adapted to different habitats,
/e.g. Tasmanian wolf (marsupial) and placental wolf (placental
mammals). 1+1

26.(i) Highlight the role of thymus as a lymphoid organs.

(ii) Name the cells that are released from the above mentioned gland. Mention, how they help in
immunity?
Answer:
(i) Thymus is a primary lymphoid organs of the immune system. Here, immature lymphocytes
get differentiated into antigen-sensitive T-lymphocytes.1
(ii) T-lymphocytes are released from thymus, after their maturation get completed. They
themselves do not produce antibodies, but help B-cells to produce them. They are also
responsible for Cell Mediated Immune (CMI) response.1+1

Or

Name the parasite that causes filariasis in humans. Mention its two diagnostic symptoms. How is
this transmitted to others?
Answer:
Wuchereria (W. bancrofti and W. malayi) is the filarial worm that causes filariasis in humans.1
Diagnostic Symptoms

● The presence of nematodes in lymph vessels causes collection of fluid. /It may
lead, to swelling in arms, breasts, legs and genital region.1Inflammation of lower
limbs result in deformities./It is transmitted to a healthy person through the bite of
the female mosquito vector, Culex. ½+ 1+½

27. Mention any three purposes for which Transgenic animals are produced
Answer:
(a) Transgenic animals are designed to allow the study of how genes are regulated and how they
affect the normal functions of the body and its developments, e.g. information is obtained as to
how insulin has a role as a growth factor. 1
(b) Transgenic animals are designed to increase our understanding of how genes control the
development of diseases; they serve as models for human diseases.1
(c) Transgenic mice are being developed to test the safety of vaccines, e.g. polio vaccine has
been tested on mice.1
28. (a) “India has greater ecosystem diversity than Norway.” Do you agree with the statement ?
Give reasons in support of your answer.
b)Write the difference between genetic biodiversity and species biodiversity that exists at all the
levels of biological organisation.
Ans. (a) Yes = ½

India / tropical region Norway / temperate region

- are less seasonal - more seasonal /

/ more constant / more predictable / less constant / less predictable

- promote niche specialisation - do not promote niche specialisation leading to

greater bio-diversity leading to low bio-diversity

- Species diversity increases as we - Species diversity decreases as we

move towards equator move away from equator

- More number of species exist - Less number of species exist

(Any one) = ½

(b) Genetic diversity - Diversity / variation within a species over its distributional range /
same explained with the help of a correct example = 1

Species diversity - Diversity / variation at a species level / same explained with the
help of a correct example = 1

[1 + 2 = 3 marks]

Section D

29. During a study on the inheritance of two genes, the teacher asked students to perform an
experiment. The students crossed white-eyed, yellow-bodied female Drosophila with a red-eyed,
brown-bodied male Drosophila (i.e., wild). They observed that progenies in F2 generation had
1.3 percent recombinants and 98.7 percent parental type combinations. The experimental cross
with results is shown in the given figure.
(i) By conducting the given experiment, the teacher can conclude that
A. Genes for eye color and body color are linked
B. Genes for eye color and body color show complete linkage
C. Linked genes remain together and are inherited
Answer: (c) A and C only

(ii) Why Teacher asked to conduct an experiment on Drosophila .Give any two reason.
(a) the male and female flies are easily distinguishable
(b) it completes its life cycle in about two weeks
(c) ) a single mating could produce a large number of progeny flies
(iii) Genes white-eyed and yellow-bodied located very close to one another on the same
chromosome tend to be transmitted together and are called
Answer: (c) linked genes

(iv) Percentage of crossing over is more when

linked genes are located far apart from each other

Or

why Mendel did not recognize linkage phenomenon in his experiments

characters he studied were situated on different chromosomes

30. In a study to test a new vaccine against a viral disease, mouse model testing is done. In this
process, mice are vaccinated and their blood samples were tested. Mice developed mild disease
symptom. After few days those mice were again infected with the virus. This time they do not
show any disease symptoms. Their blood samples were tested. Two graphs show antibody
concentration for the first and second infection in mice blood.
Based on the above information, answer the following questions.

(i) P and Q in the given graphs indicate_____

(ii) Which form of pathogen is used in vaccination?

(iii)Name the immunogloblin cross the placenta from mother to fetus?

(iv) How does vaccination work?
or

(v) How do cytokine barriers provide immunity in humans?

AnswerAnswer:
(i) : Initial contact with an antigen causes primary immune response. In primary immune
response, no antibodies are present initially. Then, a slow rise in the antibody titer occurs, first
IgM and then IgG, followed by a gradual decline in antibody titer. In secondary immune
response, the antibody formation is accelerated and more intense. This is also called booster
response. It mainly consists of IgG antibodies. 1
(ii) Vaccine is a preparation or extract of an inactivated/ attenuated (weakened) pathogen of a
disease which on inoculation into a healthy person provides immunity by inducing antibodies
production. 1
(iii) IgG is the only class of antibody to cross the placenta from mother to fetus. 1
(iv) During vaccination, when the immune system first encounters an infectious microbe, it
responds against it and then remembers it specifically. So the next time that particular microbe or
its close relatives enter the body, the immune system responds with greater vigor. this eliminates
the infection even more quickly than the first occurrence of the disease. 1
or
(v) Cytokine barriers include interferons, which are secreted by virus infected cells. They provide
protection to non-infected cells from further same viral infection.

Section E

31. (a) Describe any two devices in a flowering plant which prevent both autogamy and
geitonogamy.

(b) Explain the events upto double fertilisation after the pollen tube enters one of the
synergids in an ovule of an angiosperm.
Ans. (a) - Dioecy / production of unisexual flowers (in different plants)

- Self incompatibility = 1 + 1

(b) - Pollen tube releases 2 male gametes in the cytoplasm of synergid

- One male gamete fuses with egg cell / syngamy , resulting in diploid zygote
- Other male gamete fuses with polar nuclei / triple fusion , to form triploid
PEN (Primary Endosperm Nucleus) / PEC (Primary Endosperm Cell) = 1 × 3

[2 + 3 = 5 marks]

OR

(a) Explain menstrual cycle in human females.

(b) How can the scientific understanding of the menstrual cycle of human females help as
a contraceptive measure ?

Ans. (a) - Menstrual Phase - Menstrual flow occurs / due to breakdown of

endometrial lining of uterus , when fertilization does not occur

- Follicular Phase - Primary follicles grow into mature graafian follicles and
endometrium regenerates through proliferation , changes induced by pituitary
and ovarian hormones

- Ovulatory Phase - LH surge , induces rupture of graafian follicle and release of

secondary oocyte / ovum during middle of cycle (i.e. 14th day)

- Luteal phase - Ruptured graafian follicle transforms into corpus luteum which
secrete large amount of progesteron , essential for maintaining endometrium = 1
×4

b)Because ovulation occurs during mid cycle chances of fertilisation are very high so
, couples should abstain from coitus between day 10 - 17 = ½ + ½

(3 + 2 = 5 marks)

32. Explain the genetic basis of blood grouping in human population.

Ans. (i) Blood group in human population determined by gene ‘ I ’ , which has three allele IA and
IB and i (multiple allelism) =½ + ½
(ii) IA IB are dominant allele (codominance) each forming different type of sugar polymer
on the surface of RBC , while allele ‘ i ’ is recessive and does not produce any sugar
=½+½
IA IA , IA i –– A group = ½
 IB IB , IB i –– B group = ½
IA IB ––– AB group =
½
ii –– O group = ½
(iii) Since humans are diploid / each person possesses any two of three ‘ I ’ gene alleles ,
resulting into six different genotypic combination and four phenotypic expression =
½+½
OR

(a) State the ‘Central dogma’ as proposed by Francis Crick. Are there any exceptions to it
? Support your answer with a reason and an example.

(b) Explain how the biochemical characterisation (nature) of ‘Transforming Principle’

was determined, which was not defined from Griffith’s experiments.

Ans. (a) =1

Yes , in some viruses flow of information is in reverse direction / reverse transcription

=½+½

e.g. Any Retrovirus / HIV = ½

(b) Protein and DNA and RNA were purified from heat killed S strain / smooth
Streptococcus / Diplococcus pneumoniae = ½

Protein + Protease transformation occured (R cell to S type) = ½

RNA + RNA ase transformation occured (R cell to S type) = ½

DNA + DNA ase transformation inhibited = ½

Hence DNA alone is the transforming material = ½

[ 2 + 3 = 5 marks]

(c) independent of the other pair of characters = 1

33. a.Mention the role of (i) selectable marker, (ii) Ori and (iii) rop in E. coli cloning vector
pBR322.
Ans i) Selectable marker - helps in identifying and eliminating non transformants and selectively
permitting the growth of the transformants = 1
ii) Ori - helps to start replication and any piece of DNA when linked to this sequence
can be made to replicate within host cell, responsible for controlling the copy
number of the linked DNA = ½ + ½
iii) rop-codes for the proteins involved in the replication of
the plasmid = 1

b.Explain the roles of the following with the help of an example each in recombinant DNA
technology:

i)Restriction Enzymes ii)Plasmids

Ans. (i) It recognises a specific sequence of base pairs / pallindromes, and cuts the DNA strand
at a specific site. eg. EcoRI / Hind II or any other correct example = ½ + ½

(ii)Act as vectors / cloning of desired alien gene / foreign gene = 1 eg. pBR322 /
plasmid of Salmonella / plasmid of Agrobacterium / Ti Plasmid / Tumour inducing
Plasmid =½ + ½
or
(a)biological control of diseases and pests to the use of chemicals for the same purpose. Justify.

(b) Give an example of a bacterium, a fungus and an insect that are used as biocontrol
agents.

Ans. (a) - Reduces dependence on toxic chemicals

- Protects our ecosystem or environment

- Protects and conserves non-target organisms / they are species - specific

- These chemicals being non-biodegradable may pollute the environment

permanently

- These chemicals being non-biodegradable may cause biomagnification

(Any four) = ½ × 4

(b) Bacteria – Bacillus thuringiensis = 1

Fungus – Trichoderma = 1

Insect – Ladybird / Dragonfly / Moth or any other correct example = ½ +½ 5marks]

__________________________________________________________________________