KENDRIYA VIDYALAYA SANGATHAN, ERNAKULAM REGION

Half Yearly Examination 2024-25

Subject: Biology Class: XII

Time: 03 Hrs. Max.Marks:70M
Name of student: _____________________________ Roll No:__________

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.
(v) Wherever necessary, neat and properly labeled diagrams should be drawn.
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SECTION A
1. Identify the activity of endonuclease and exonuclease in the given image. 1M

2. An IUD recommended to promote cervix hostility to the sperm is: 1M

a. Cu T b. Multiload-375 c. LNG-20 d. Cu
3. If a genetic disease is transferred from a phenotypically normal but carrier female 1M
to only some of the male progeny the disease is
a. Autosomal dominant b. Autosomal recessive
c. Sex-linked dominant d. Sex-linked recessive
4. In which of the following ways is natural selection not analogous to artificial 1M
selection?
a. With natural selection ”picking” is due to the fit of an organism with its
environment; whereas in artificial selection, the breeder “picks” which
organisms will breed.
 b. Natural selection depends upon the presence of variation, artificial selection
does not.
c. Natural selection occurs within populations, artificial selection does not.
d. There is a limit to how much change can be brought about by natural
selection, no such limit exists for artificial selection.
5. Non-specific host defence that exists prior to the exposure of an antigen is called: 1M
a. acquired immunity b. passive immunity
c. innate immunity d. active immunity
6. How many types of gametes can be produced by a diploid organism who is 1M
heterozygous for 4 loci?
a. 4 b. 8 c. 16 d. 32
7. Globozoospermia is a rare condition that affects only males. It is characterized by 1M
sperm cells having a round head and no acrosome. What would this condition lead
to?
a. inability of the sperms to fertilise the egg
b. inability of the male to produce enough sperms
c. formation of zygote that is haploid instead of diploid
d. formation of zygotes with a missing sex chromosome
8. BOD of waste water is estimated by measuring the amount of 1M
a. total organic matter b. biodegradable organic matter
c. oxygen evolution d. oxygen consumption
9. If the sequence of nitrogen bases of the coding strand of DNA in a transcription 1M
unit is: 5’– ATG ATG – 3’, the sequence of bases in its RNA transcript would be
a. 5’ – AUG AAUG – 3’ b. 5’ – UACUUAC – 3’
c. 5’ – CAUCAU – 3’ d. 5’ – GUAGUA – 3’.
10. A female undergoing IVF treatment has blocked fallopian tubes. The technique by 1M
which is best suited for the female to become pregnant is:
a. ZIFT b. GIFT c. IUT d. AI
11. Which one of the following is an example of carrying out biological control of 1M
pests/diseases using microbes?
a. Trichoderma sp. against certain plant pathogens.
b. Nucleopolyhedrovirus against white rust in Brassica.
c. Bt-cotton to increase cotton field.
d. Lady bird beetle against aphids in mustard.
12. Shown here is how the levels of hormones Estrogen and Progesterone change 1M
during the menstrual cycle.
 Which of these correctly shows how the levels of Luteinizing hormone (LH) and
Follicle-stimulating hormone (FSH) change during the same cycle?

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 (A)- Cleistogamous flowers produce assured seed set in the absence of 1M
pollinators.
Reason (R)- Cleistogamous flowers do not open at all.
14. Assertion (A)- Polycistronic mRNA is capable of forming a number of polypeptide 1 M
chains.
Reason (R)- Polycistronic mRNA has termination codons.
15. Assertion (A)- Smoking increases the carbon monoxide (CO) content in the blood 1M
which has greater affinity to haemoglobin than oxygen.
Reason (R)- CO forms a stable bond with haemoglobin and does not allow binding
of oxygen.
16. Assertion (A)- Insecticides and antibiotics remain effective for an unlimited period. 1 M
Reason(R)- Organisms loose sensitivity to insecticides and antibiotics.
SECTION B
17. The frequency of recombination is very low though the genes are grouped on the 2M
same chromosomes. Comment on it.
18. A woman has certain queries as listed below, before starting with contraceptive 2M
pills. Answer them.
a) What do contraceptive pills contain and how do they act as contraceptives?
b) What schedule should be followed for taking these pills?
19. Write the binomials of two fungi and mention the products/ bioactive molecules 2M
they help to produce.
20. Write the names of the following 2M
a) 15 mya primates that were ape-like and man-like.
b) Organs with the same structural design and origin but different function.
c) Single step large mutation.
21. The image below shows the result of plating bacteria in chromogenic medium after 2M
incorporating the gene of interest in plasmid. Some plates had blue colonies; some
plates had white colonies. A single bacterium extracted from Plate I, II, III is shown
below:

On the basis of your observations

a) Identify the plate(s) which is/are white. Give a reason.
b) Identify the plate(s) which is/are blue. Give a reason.
SECTION C
22. Flowering plants have developed many devices to discourage self-pollination. 3M
Briefly describe any four floral features that discourage self-pollination.
23. a) Name a drug used 3M
(i) As an effective sedative and pain killer
(ii) For keeping patients to cope with mental illness like depression but often
misused
b) Name the plant source of - smack and ganja
24. a) Why are both the strands of DNA not copied during transcription? 3M
b) Why is it not possible for an alien DNA to become a part of chromosome
anywhere along its length and replicate normally?
25. (i) Explain the convention for naming EcoRI. 3M
(ii) With the help of an illustration only, show the action of EcoRI on a DNA
Polynucleotide.
26. The image below depicts the result of gel electrophoresis 3M

If the ladder represents sequence length upto 3000 base pairs (bp),
a. Which of the bands (I - IV) correspond to 2500 bp and 100 bp respectively?
b. Explain the basis of this kind of separation and also mention the significance of
this process.
27. The technique of amniocentesis revealed the presence of 47 chromosomes in the 3M
foetal cells collected from an individual. Name the two possible chromosomal
disorders of this foetus. How does the karyotype and symptoms differ in these two
disorders?
28. Explain the different steps involved in sewage treatment before it can be released 3M
into natural water bodies.
SECTION D
29. A flower of tomato plant following the process of sexual reproduction produces 4M
240 viable seeds. The viable seeds are those which have the ability to remain alive
and may develop into plants and reproduce themselves in the given appropriate
conditions. This happens when one of the pollen grains reaches the stigma by any
agency at 2-celled stage vegetative cell and generative cell. The generative cell
divides mitotically and forms two male gametes which enters into the ovule after
passing through the pollen tube and undergoes the process of double fertilization in
the ovule. The ovule is a large parenchymatous body formed in the ovary by
megasporogenesis. The megaspore mother cell in an ovule is a diploid structure
which undergoes meiotic division and forms one functional megaspore. The
megaspore undergoes three subsequent divisions and forms 8 nuclei arranging
themselves in 3 groups. After fertilization, the ovule converts into the seed and
whole ovary develops into a complete fruit.
a) How many would be the minimum number of pollen grains that must have
been involved in the pollination of its pistil?
b) What will be the minimum number of microspore mother cells that must
have undergone reductional division prior to dehiscence of anther?
c) How many male gametes might have been involved in this case?
d) How many Megaspore mother cells are involved in this process?
e) What will be the minimal number of ovules present in the ovary?
30. According to Hardy Weinberg principle, the allele frequencies in a population are 4M
stable and remain constant through generations. When the frequency differs from
the expected values, the difference indicates the extent (direction) of evolutionary
 change. Disturbance in the genetic equilibrium or Hardy Weinberg equilibrium in a
population can be interpreted as resulting in evolution.
a) Represent the formula of Hardy Weinberg equilibrium.
b) In a population of 1000 individuals, 360 belong to genotype AA, 480 to Aa
and the remaining 160 to aa. Based on this data, what will be the frequency
of allele A in the population?
c) Briefly explain any three causes for disturbances in Hardy Weinberg
equilibrium that results in evolution.
SECTION E
31. a) Mention the role of z,y,a and i genes in Lac operon. 5M
b) How does the addition of lactose to the culture medium of E.coli induce the
expression of three structural genes? Explain with a diagram
(OR)
State the Law of independent assortment. Explain with the help of an example.
32. a) Describe the events of spermatogenesis with the help of a schematic 5M
representation.
b) Write two differences between spermatogenesis and oogenesis.
(OR)
a) Name and explain the role of inner and middle walls of the human uterus.
b) List the different parts of the human oviduct through which the ovum
travels till it meets the sperm for fertilisation.
c) Immediately after implantation what does the embryo develop into?
Where are Stem cells seen during development?
33. The pathogen of a disease depends on RBCs of humans for growth and 5M
reproduction. The person with this pathogen suffers with chills and high fever.
(a) Identify the disease.
(b) Name the pathogen.
(c) What is the cause of fever?
(d) Represent the life cycle of the pathogen diagrammatically.
(OR)
a) An organic farmer relies on natural predation for controlling pests and
diseases. Justify giving reasons, why is this considered to be a holistic
approach?
b) How do macrophages in the human body act as HIV factory?
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