CBSE Board Class 12 Biology Previous Year Question Papers 2008

BIOLOGY (Theory) previous paper 2008
Time allowed : 3 hours Maximum Marks : 70
General Instructions :
(i) This question paper consists of four sections  A, B, C and  D. Section  A contains
5  questions of one mark each, Section  B is of  10 questions of  two marks each,
Section  C is of  10 questions of  three marks each and Section  D is of  3 questions
of  five marks each.
(ii) All questions are compulsory.
(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 one question of  5 marks weightage.
Attempt only one of the choices in such questions.
(iv) Question numbers  1 to  5 are to be answered in  one word or  one sentence each.
(v) Question numbers  6 to  15 are to be answered in approximately  20-30 words each.
(vi) Question numbers  16 to  25 are to be answered in approximately  30-50 words each.
(vii) Question numbers  26 to  28 are to be answered in approximately  80-120 words
each.

SECTION A
1. Why does thinning of bones usually start occurring in human females at about 50 years
of age ? 1

2. Drosera  carries out photosynthesis and still traps insects. Why ? 1

3. What causes Gouty Arthritis in humans ? 1

4. List two factors that determine the vegetation and soil type of an ecosystem. 1

5. Why is gene encoding for “Cry” protein inserted into a crop plant ? 1

SECTION B
6. What is multiplicative growth ? How is it different from auxetic growth ? 2

7. What is  the  source  of explants  in  a meristem  culture  ?  Mention  one  function  of
cytokinins used in the meristem culture medium. 2

8. Why do temperate regions show a lower value of primary productivity as compared to
tropical regions ? Give two reasons. 2

9. What is biogas ? Give its composition. Why is biogas preferred to other conventional
energy fuels ? 2

10. An Rh-negative mother has safely delivered her first Rh-positive child. Discuss the
problems that can arise as a result of it and can affect a subsequent pregnancy. 2

11. Explain symbiotic nitrogen fixation in leguminous plants. 2

12. What is oxidative decarboxylation ? What happens to pyruvate immediately after this
reaction ? Name the enzyme involved in this reaction. 2

13. What is the end product of glycolysis in aerobes, and where does this process occur ?
List the conditions under which fermentation occurs in plant cells. 2
OR
Where exactly does electron transport system operate in Mitochondria ? What is the role
of oxygen and F 0 - F 1
in this pathway ? How many molecules of ATP are produced when
one molecule of NADH goes through this path ?

14. Name the causal organism of tiek fever in animals. Give two symptoms of the disease in
acute form. Name the body cells the pathogen attacks. 2

15. List any two functions of thyroid gland in humans. Name the condition caused due to
Hyperthyroidism and give its one symptom. 2

SECTION C
16. Name the hormone that stimulates the human gall bladder to release bile juice. How
does this juice reach the duodenum ? Explain the function of bile juice in food
digestion. 3

17. In what form is Magnesium absorbed by plants from the soil ? Give two functions of
Magnesium in plants and its two deficiency symptoms. 3

18. Explain the principle of Sonography. 3

19. Give the location and function in the human eye, of the following : 3
(i) Cornea
(ii) Iris
(iii) Vitreous humor

20. Distinguish between Alpha and Beta diversity in an ecosystem. What is the significance
of large genetic diversity in a population ? 3
OR
What are Algal Blooms ? How are they formed ? Give two harmful effects of formation
of Algal Blooms in an aquatic body.

21. Plantlets produced in the laboratory need to be hardened before transplanting them in
the field. Explain why they need to be hardened and how it is carried out. 3

22. What are the two intrinsic mechanisms that provide autoregulation of glomerular
filtrate ? Explain any one of these. 3

23. Name the type and give the effects of the following drugs on humans : 3
(i) LSD
(ii) Morphine
(iii) Barbiturates

24. What is the ecological succession of bare rock technically called ? Name the first and the
last-but-one succession stages in it. Explain how the climax community gets established
in this succession. 3

25. Differentiate between quiescent and dormant seeds. Give any four reasons why some
seeds need to undergo dormancy. 3

SECTION D
26. Draw labelled diagrams of the following :
(i) T.S. of bilobed anther of an angiosperm
(ii) Internal structure of a pollen grain of an angiosperm 5
OR
Draw a flow-chart showing hormonal control of human female reproductive system.
Highlight the positive and negative feedback mechanism in it.

27. What is cardiac cycle ? Explain the different steps involved in the pumping action of the
heart during a single cardiac cycle. 5
OR
(i) What is residual volume ? How much is it in a normal human adult ?
(ii) Explain the role of diaphragm and ribcage in inspiration and expiration in humans.

28. Explain the mechanism of closing and opening of stomata. Name the category of plants
which keep their stomata open during the night and closed during the day. 5
OR
Explain the mechanism of C
photosynthetic carbon cycle. Name any two plants where
it occurs. Mention the difference in the structure of chloroplasts in the mesophyll cells
and bundle sheath cells in such plants.