केन्द्रीय विद्याऱय संगठन, कोऱकाता संभाग

KENDRIYA VIDYALAYA SANGATHAN, KOLKATA REGION

प्री बोर्ड परीक्षा / PRE BOARD EXAMINATION - 2024-25
कक्षा/CLASS- XII अधिकतम अंक/MAX. MARKS – 70

बबषय/SUBJECT – BIOLOGY/ जीि विज्ञान समय/TIME – 3

HOURS
General Instructions:
(i) All questions are compulsory.
(ii) The question paper has five sections and 33 questions.
(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; & 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.
(v) Wherever necessary, neat and properly labelled diagrams should be drawn.
Section–A
Q.No QUESTION MARK
1. The spermatids transform into spermatozoa by the process of 1
a) spermiation b) spermatogenesis c) spermiogenesis d) spermatitis
2. Dioecy(dioecious condition) in plants prevents. 1
a. autogamy but not geitonogamy b. geitonogamy but not autogamy
c. both autogamy and geitonogamy d. neither autogamy nor geitonogamy
3. A colour blind girl is very rare because she will be born only when 1
a) Her mother and maternal grandfather are colour blind
b) Her father and maternal grandfather are colour blind
c) Mother is colour blind but father has normal vision
d) Her parents are normal but grandparents are colour blind
4. A mRNA of repeating sequence 5’ACACACACACAC….. is used for protein 1
synthesis in a cell free system and assuming that no initiation codon is
required, what type of products will be formed
a) One protein consisting of one type of amino acids
b) Two protein consisting of one type of amino acid
c) Two proteins consisting of two alternating types of amino acid
d) one protein consisting of two alternating types of amino acid
5. What is true about the surgical method of contraception? 1
I) also called sterilisation
ll) terminal method of contraception
III) block game transport
lV) tubectomy in males and vasectomy in female
V) high reversibility and contraceptive value
a) l,ll,lll,lV b) l,ll,lll,V c) l,ll,lll,lV,V d) l,ll,lll
6. The thorn of bougainvillaea and spines of cactus are examples of 1
a) divergent evolution b) convergent evolution
c) adaptive radiation d) vestigial organs
7. Removal of RNA polymerase-lll from nucleoplasm will affect the formation of 1
a. tRNA b. rRNA c. mRNA d. hnRNA

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 8. Which of the statements do not follow the criteria of genetic material 1
a. It should be able to generate its replica.
b. It should chemically and structurally be stable.
c. It should undergo recombination which is required for evolution.
d. It should provide scope for fast changes.
9. Which statement is incorrect about Nucleopolyhedrovirus 1
a)They are pathogenic virus b)They are broad spectrum
c) They are species specific d) They have no effect on non-target
organism
10. In the Hershey and Chase experiment, what findings led to conclude 1
that DNA is the genetic material.
a) presence of radioactivity in bacteria when 35S was used
b) presence of radioactivity in supernatant when 35S was used
c) presence of radioactivity in bacteria when 32P was used
d) presence of radioactivity in supernatant when 32P was used
11. While isolating DNA from bacterial cell, which of the following enzymes 1
should not be used
a) Lysozyme b) Ribonuclease c)Protease d) Deoxyribonuclease
12. Which statement regarding insertional inactivation of β-galactosidase is 1
correct?
a) production of a blue colour indicate insertion of gene
b) production of a white colour indicate insertion of gene
c) production of a yellow colour indicate insertion of gene
d) colour doesn't indicate insertion or non-insertion.
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: Assertion :The recombinant DNA technology has made immense 1
contribution in Healthcare by enabling mass production of safe and
therapeutic drugs
Reason: The recombinant therapeutic drugs do not induced any side effects
like similar products obtained from some other non-human sources
14. Assertion: Assertion: Interferons are a type of antibodies produced by body 1
cells infected by bacteria.
Reason: Interferons play an important role in the immune response of the
body.
15. Assertion: Assertion : UAA, UAG and UGA terminate protein synthesis 1
Reason : They are not recognised by tRNA.
16. Assertion: Pyramid of biomass is always upright for tree ecosystem. 1
Reason: Total biomass of a tree in a specific area is more than that of
herbivore
Section–B
17. Attempt either option A or B. 2
A. Consider two plants species as described below:
Species P: bisexual, cleistogamous
Species Q: unisexual, chasmogamous
What kind of pollination is likely to be seen in species P and Q. Give a
reason for your answer in each case.

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 OR
B. The table below outlines some milestones of pregnancy.
Day 1 fertilisation
Day 2 morula is formed
Day 5 inner cell mass is formed
Day 7 implantation
Pregnancy tests detect the presence of the human chorionic gonadotropin
(hCG) in blood or urine to confirm.
(a) A pregnancy test done after which day is likely to yield a positive result?
Give reasons.
(b) Explain why hCG is used for pregnancy tests?
18. Attempt either option A or B. 2
A. Sex determination in cockroaches is the same as that seen in some other
insects like grasshoppers.
(a) Illustrate a cross between a female (XX) cockroach and a male (XO)
cockroach.
(b) Chalk out what will be the chromosome number of the offspring
formed, if the number of autosomes is 22?
OR
B. Justify the following statements:
(a) mRNA synthesis happens in the nucleus but protein synthesis
happens outside the nucleus.
(b) Splicing of the hn-RNA is an important post-translational modification.
19. Mention where the following events in the life cycle of Plasmodium takes 2
place (organ and host)
a) Gametocyte formation b) Fertilisation
20. GM crops enhance the nutritional value of food like golden rice which is 2
Vitamin ‘A’ enriched rice. State any other four advantages of using genetically
modified crops.
21. Attempt either option A or B. 2
A. (a) State 2 criteria which are required to designate an area as biodiversity
hotspot.
(b) Name any 2 hotspots which are located in India.
OR
B. Population density is calculated by the following formula:
Nt+1 = Nt + [(B+I)-(D+E) . Imagine a population of fish in an artificial lake
which acts as a closed system.
(a) Which quantity or quantities of the above formula will NOT be used in
calculating the population of fish?
(b) Give reason.
Section–C
22. The following is the illustration of the sequence of ovarian events ‘a’ to 3
‘i’ in human female:

i) Identify the figure that illustrates Corpus luteum

ii) Name the pituitary hormone that influences its formation.
iii) Specify the endocrine function of corpus luteum.

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23. Fill in the blanks-a, b, c, d e f,: 3
Name of the Product Purpose
Microbe
Streptococcus Streptokinase a
b Statin c
d Citric acid Used in food industry
Trichoderma e Immunosuppressive drug
polysporum
f Used in detergents to remove oil stains
24. Polymerase chain reaction (PCR) is an in-vitro technique used to 3
amplify nucleic acid sequences. The conditions and duration of each
step in PCR are as follows:
- Step 1 at 94 °C for 2 min
- Step 2 at 50-65 °C for 30 seconds
- Step 3 at 72 °C for 5 min
a) Name the 3 steps of PCR.
b) Why does step 1 require such a high temperature?
c) Which enzyme is used for the process and name the source of
the enzyme?
25. Study the figure given below and answer the questions. 3

(a) Why is the lac gene called polycistronic?

(b) Which enzymes are produced by gene z and gene a ?
(c) What happens to the expression of the lac operon when the
inducer is present?
26. 3
a) Label ‘A’ and ‘B’ A
b) What stage of embryo does
the above figure represent? B
State its importance
c) State the fate of ‘C’. C

27. 3
i) Identify A and B
ii) Name the scientist who
performed the experiment. What
was the end product?
iii) Which theory was proved by the
above experiment?

28. a) Define detritus. 3

b) List the steps in the process of conversion of detritus into simple
inorganic substances.

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 Section–D
Q. No. 29 and 30 are case-based questions. Each question has 3 subparts with internal
choice in one subpart.
29. Observe the diagram that depicts a type of association between the 4
roots of plants and fungi
a) What is the term used to define the
above mentioned association?
b) What type of population interaction
do the above associations symbolise?
Attempt either subpart C or D.
c) Cite any other 2 examples showing
similar types of population interaction.
OR
d) State two ways in which the plant
benefits from their association with fungi?
30. The picture shows the plasmid pBR322 which is a commonly used plasmid 4
cloning vector in E.coli . The molecule is a double-stranded circular DNA with
4361 base pairs in length.
a) Label ‘a’ in the above diagram? What is
it used in r DNA technology?
b) A biotechnologist wanted to create a
colony of E.coli possessing the plasmid
pBR322, sensitive to Tetracycline.
Which restriction sites would he use to
ligate a foreign DNA ?
Attempt either sub part C or D.
c) Define the terms ‘ori’ and ‘rop’
OR
d) What are ‘b’ and ‘c’ in the above figure and what is their
function?
Section–E
31. Attempt either option A or B. 5
A.The given picture is of T.S. of
anther showing its wall layers.
a) Label ‘a’ and ‘b’
b) Construct a schematic representation
of the process of microsporogenesis
starting with the pollen mother cell up
to the formation of pollen grains.
c) Calculate the number of microspore mother cells required to produce 1600
pollen grains.
d) Analyse what would happen if due to mutation, the component ‘b’ of the
above diagram was formed defective.
OR
B. The graph given below shows the variation in the levels of ovarian
hormones during various phases of menstrual cycle:

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 (a) Identify ‘A’ and ‘B’.
(b) Specify the source of the hormone marked in the diagram.
(c) Reason out why A peaks before B.
(d) Compare the roles of A and B.
(e) Under which condition will the level of B continue to remain high on
the 28th day?
32. Attempt either option A or B. 5
A. Two blood samples A and B picked up from the crime scene were handed
over to the forensic department for DNA fingerprinting. Mention the 6 main
steps of DNA fingerprinting. What is the full form of VNTR and what is its use
in DNA fingerprinting?
OR
B. i) Four children with four different blood groups are born to parents where
the mother has blood group B and the father has blood group A.
Construct a cross to show the genotypes of the parents & all four children.
Mention the genotypic and phenotypic ratio.
ii) Taking the example of blood groups explain the concepts of multiple alleles
and codominance.
33. Attempt either option A or B. 5
A. The outline structure of a drug is given below.

i) Identify the drug.

ii) How is the drug used in
medical science?
(iii) Name the plant from which
this drug is obtained.
(iv) When the above drug is misused, it may lead to dependence and
manifest unpleasant withdrawal syndrome. Explain dependence and
withdrawal syndrome in context of drug abuse.
OR
B. (a) Compare between active and passive immunity giving two important
points of difference.
(b) Is vaccination active or passive ? Give reason
(c) Diagrammatically trace the sequence of events that occurs when HIV
gains entry into a particular cell type inside the human body.

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