CBSE Board Class 12 Biology Sample Paper For 2023-24 Board Examination

CBSE Board Class 12 Biology Sample Paper For 2023-24 Board Examination
Sample Question Paper 2023-24
Class XII
Biology (Subject Code-044)

Maximum Marks: 70
Time: 3 hours

(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.

Section – A

1. Remnants of nucellus are persistent during seed development in:
a) pea
b) groundnut
c) wheat
d) black pepper

2. The wall layer of microsporangium which nourishes the pollen grain is:
a) epidermis
b) endothecium
c) middle layers
d) tapetum

3. A short piece of DNA, having 20 base pairs, was analyzed to find the number of
nucleotide bases in each of the polynucleotide strands. Some of the results are
shown in the table.

How many nucleotides containing Adenine were present in strand 2?
a) 2
b) 4
c) 5
d) 7

4. In a certain species of insects, some have 13 chromosomes, and the others have
14chromosomes.The 13 and 14 chromosome bearing organisms are
a) males and females, respectively
b) females and males, respectively
c) all males
d) all females

5. At a particular locus, the frequency of allele A is 0.8 and that of allele a is 0.2.
What would be the frequency of heterozygotes in a random mating population at
a) 0.32
b) 0.16
c) 0.24
d) 0.48

6. Variations caused due to mutations are
a) random and directionless
b) random and directional
c) random and small
d) random, small and directional

7. What is the smallest part of a DNA molecule that can be changed by a point
a) Oligonucleotide
b) Codon
c) Gene
d) Nucleotide

8. What should be the genotype of the indicated member?

a) AA
b) Aa
c) XY
d) aa

9. A patient was advised to have a kidney transplant. To suppress the immune
reaction, the doctor would administer him:
a) statins produced from Monascus purpureus
b) statins produced from Streptococcus thermophilus
c) cyclosporin A produced from Trichoderma polysporum
d) cyclosporin A produced from Clostridium butylicum

10. Identify the activity of endonuclease and exonuclease in the given image.

11. The main objective of production of pest resistant GM crops is to
a) encourage eco-friendly pesticides
b) reduce pesticide accumulation in food chain
c) eliminate pests from the field without the use of manual labour
d) retain maximum nutritional content in the crop that would be otherwise
consumed by pest

12. Observe the contents 1,2,3 and 4 of soil samples A,B and C shown in the graph. If
the temperature and soil moisture of all soil samples are identical, which soil
sample (s) will show faster decomposition?

a) Soil Sample A
b) Soil Sample B
c) Soil Samples A and B both
d) Soil Sample C

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: Primary endosperm nucleus is diploid.
Reason: It is the product of double fertilisation

14. Assertion: Ribosomal RNA is synthesized in the nucleus of the cell.
Reason: It is translated with the enzyme RNA polymerase III.

15. Assertion: Smoking can raise blood pressure and increase heart rate.
Reason: Nicotine stimulates adrenal glands to release adrenaline and noradrenaline into the blood circulation, both of which raise blood pressure and
increase heart rate.

16 Assertion: PCR is a powerful technique to identify genetic disorders.
Reason: PCR can detect mutations in low amounts of DNA.

Section – B

17. Explain the process of hormonal regulation of spermatogenesis.

18. The diagram below shows the sequence of amino acids in part of a haemoglobin molecule.

a) If the base T* was substituted with A, how would it affect the haemoglobin chain?
b) Name the condition and the effects associated with the above substitution.

19. The graph given below indicates the administration of the first (L) and second dose (M) of a vaccine. The corresponding response of the body is indicated by X and Y. Interpret the graph and explain the reason for such a response shown by the body.

20. The image below shows the result of plating bacteria in chromogenic medium after 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.

21. Biomass of a standing crop of phytoplankton is 4 kg/m2 which supports a large
standing crop of zooplankton having a biomass 11 kg/m2 This is consumed by
small fishes having biomass 25 kg/m2 which are then consumed by large fishes with
the biomass 37 kg/m2 Draw an ecological pyramid indicating the biomass at each stage and also name the
trophic levels. Mention whether it is an upright or inverted pyramid.

Section – C

22. he figure given below shows 3 sperms A, B and C.
a) Which one of the three sperms will gain entry into the ovum?
b) Describe the associated changes induced by it on P and Q.

23. Explain the phases in embryonic development from the morula stage till the establishment of pregnancy in a human female.

24. A pregnant human female was advised to undergo MTP. It was diagnosed that the fetus she was carrying had developed from a zygote having 45 chromosomes with only one X chromosome.
a) What is this condition called and how does it arise?
b) Why was she advised to undergo MTP?

25. The graphs below show three types of natural selection. The shaded areas marked with arrows show the individuals in the population which are not selected. The dotted vertical lines show the statistical means.

a) What names are given to the types of selection shown in graphs A, B and C.
b) After the selection has operated for several generations in the above populations indicated as Graph A, B and C, graphically illustrate the probable results.

26. The aeration tank of a sewage treatment plant is not functioning properly. Explain in detail the impact of this on the treatment of sewage and BOD of the effluent.

27. A farmer grew 2 varieties of corn crop in field A and B. He grew normal corn crops in field A and GM corn crops in field B. He observed corn borers attacked only in field A. To control it, spores of Bt were sprayed in field A.
a) Name the gene in the spores responsible for the control of this pest.
b) What effect will the spores of Bt have on the insect pest?
c) How has field B developed resistance against this pest?


Lipoprotein lipase deficiency (LPLD)is a genetic disorder in which a person has a defective gene for lipase. This leads to high triglycerides, stomach pain, fat deposits under the skin. It may eventually affect the liver, pancreas and may also cause diabetes. The disorder occurs if a child acquires defective genes from both parents (autosomal recessive). ERT (enzyme replacement treatment) is one of the
treatments offered to patients with LPLD.
a) (i) What procedure is followed in ERT?
(ii) What could be one possible drawback of ERT?
b) How can LPLD be treated using Biotechnology? Elaborate.

28. Give three reasons as to why the prokaryotes are not given any figures for their diversity by the ecologists.

Section – D

Q. No. 29 and 30 are case-based questions. Each question has 3 subparts with internal choice in one

29. What will be the impact if oriin the above structure gets damaged?
b) The lac z gene has many recognition sites. Study the segment of DNA
given below and answer the questions
i) Applying your knowledge of palindrome sequences identify and mark the possible region where the restriction enzyme X will act.

ii) Restriction enzyme Y was used to extract gene of interest from a plant. This gene needs to be inserted in the given DNA segment which has been treated with restriction enzyme X. Will there be a successful recombination? Explain with a reason.

c) Which one of the two (pUC18 and pBR322) would you prefer for biotechnological studies? Justify Observe the graph given below.

30. The graph represents inter-specific interaction between two species of Paramecia competing for the same resource in a culture medium. Paramecium caudatum and Paramecium aurelia were grown in separate cultures as well as in mixed cultures. It was found that each species grew in numbers according to the logistic equation.


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