CBSE Class XII : Biology Exam Paper Year
- Time allowed : 3 hours
- Maximum Marks: 70
(i) All questions are compulsory.
(ii) This question paper consists of four Section A, B, C and D. Section A
contains 8 questions of one marks each, Section B is of 10 questions of two
marks each, Sections C is of 9 questions of three marks each and Sections D is
of 3 questions of five marks each.
(iii) There is no overall choice. However, an internal choice has been
provided in one question of 2 marks, one question of 3 marks and all the three
questions of 5 marks weightage. A student has to attempt only one of the
alternatives in such questions.
(iv) Wherever necessary, the diagrams drawn should be neat and properly
SECTION – A
1. Why hnRNA is required to undergo splicing?
2. The microscopic pollen grains of the past are obtained as fossils.
Mention the characteristic of the pollen grains that makes it happen.
3. How does colostrum provide initial protection against diseases to
new born infants? Give one reason.
Name the unlabelled areas ‘a’ and ‘b’ of the pie chart (given above)
representing the global biodiversity of invertebrates showing their
proportionate number of species of major taxa.
5. Mention the type of evolution that has brought the
similarity as seen in potato tuber and sweet potato.
6. Name the group of organisms and the substrate act on to produce
7. Mention the pollinating agent of an inflorescence of small dull
coloured flowers with well exposed stamens and large feathery stigma. Give any
one characteristic of pollen grains produced by such flowers.
8. Name the organism commercially used for the production of single
SECTION – B
9. Explain the contribution of Thermus aquaticus in the
amplification of a gene of interest.
(i) What does the above diagram illustrate?
(ii) Name the parts labelled ‘a’ and ‘b’.
(iii) Name the type of cells that produce this molecule.
11. Banana is a parthenocarpic fruit whereas oranges show
polyembryony. How are they different each with respect to seeds?
Where are fimbriae present in a human female reproductive system? Give their
12. How is the translation of mRNA terminated? Explain.
13. Explain accelerated eutrophication. Mention any two consequences of
14. List the specific symptoms of amoebiasis. Name the causative
15. A crane had DDT level as 5 ppm in its body. What would happen to
the population of such birds? Explain giving reasons.
16. Describe the responsibility of GEAC, set up by the Indian
17. During the secondary treatment of the primary effluent
haw does the significant decrease in BOD occur?
18. Study the figure given below and answer the questions:
(a) How does the repressor molecule get inactivated?
(b) When does the transcription of Lac mRNA stop?
(c) Name the enzyme transcribed by the gene ‘Z’.
SECTIONS – C
19. Name the pioneer species on a bare rock. How do they
help in establishing the next type of vegetation? Mention the type of climax
community that will ultimately get established.
20. Study the figure below and answer the questions that follow:
(a) Name the stage of human embryo the figure represents.
(b) Identify ‘a’ in the figure and mention its function.
(c) Mention the fate of the inner cell mass after implantation in the uterus.
(d) Where are the stem cells located in this embryo?
21. Give the scientific name of the parasite that causes
malignant malaria in humans. At what stage does this parasite enter the human
body? Trace its life cycle in human body.
22. Draw a labelled schematic sketch of replication fork of DNA.
Explain the role of the enzymes involved in DNA replication.
23. Explain the causes of global warming. Why is it a warning to
24. Haemophilia is a sex linked recessive disorder of humans. The
pedigree chart given below shown the inheritance of haemophilia in one family.
Study the pattern of inheritance and answer the questions given.
(a) Give all possible genotypes of the members 4, 5 and 6 in the pedigree
(b) A blood test shows that the individual 14 is a carrier of haemophilia. The
member numbered 15 has recently married the member numbered 14. What is the
probability that their first child will be a haemophilic male?
Inheritance pattern of ABO blood groups in humans shows dominance,
codominance and multiple allelism. Explain each concept with the help of blood
(a) Mention the specific geographical region where these organisms are found.
(b) Name and explain the phenomenon that has resulted in the evolution of eash
diverse species in the region.
(c) Explain giving reasons the existence of placental wolf and Tasmanian wolf
sharing the same habitat.
(a) Identify the selectable markers in the diagram of E. cli. vector shown
(b) How is the coding sequence of α-galactosidase considered a better marker
than the one identified by you in the diagram? Explain.
27. Construct an ideal pyramid of energy when 1,000,000
joules of sunlight is available. Label all its trophic levels.
SECTIONS – D
28. Explain with the help of a diagram the development of a
mature embryo sec from a megaspore mother cell in angiosperm.
Study the following flow chart. Name the hormones involved at eash stage.
Explain their functions.
Hypothalamus → Pituitary → Testes → Sperms
29. (a) Explain the experiment performed by Griffith on
Streptococcus pneumonia. What did he conclude from this experiment?
(b) Name the three scientists who followed up Griffith’s experiments.
(c) What did they conclude and how?
Two blood samples A and B picked up from the crime scene were handed over to
the forensic department for genetic fingerprinting. Describe how the technique
of genetic fingerprinting. Describe how the technique of genetic fingerprinting
is carried out. How will it be confirmed whether the samples belonged to the
same individual or to two different individuals?
30. One of the main objectives of biotechnology is to
minimize the use of insecticides on cultivated crops. Explain with the help of a
suitable example how insect resistant crops have been developed using techniques
(a) How is mature insulin different from proinsulin secreted by pancreas in
(b) Explain how was human functional insulin produced using rDNA technology.
(c) Why is the functional insulin thus produced considered better than the ones
used earlier by diabetic patients?