Biology · Sample Paper 2

General instructions

Section A · Objective

1. Question 11 mark

   The part of the pistil that receives pollen is the

   1. A.style
   2. B.ovary
   3. C.stigma
   4. D.ovule
2. Question 21 mark

   Transfer of pollen from the anther to the stigma of a different flower on the same plant is

   1. A.autogamy
   2. B.geitonogamy
   3. C.xenogamy
   4. D.cleistogamy
3. Question 31 mark

   The male sex hormone testosterone is secreted by the

   1. A.Sertoli cells
   2. B.Leydig cells
   3. C.seminiferous tubules
   4. D.epididymis
4. Question 41 mark

   The number of sperms formed from one primary spermatocyte is

   1. A.1
   2. B.2
   3. C.4
   4. D.8
5. Question 51 mark

   The genotype of a person with blood group AB is

   1. A.IᴬIᴬ
   2. B.IᴬIᴮ
   3. C.IᴮIᴮ
   4. D.ii
6. Question 61 mark

   Down's syndrome is caused by

   1. A.trisomy of chromosome 21
   2. B.monosomy of X
   3. C.XXY
   4. D.deletion of chromosome 5
7. Question 71 mark

   The enzyme that joins DNA fragments during replication is

   1. A.helicase
   2. B.DNA ligase
   3. C.DNA polymerase
   4. D.primase
8. Question 81 mark

   If a DNA molecule has 20% adenine, the percentage of guanine is

   1. A.20%
   2. B.30%
   3. C.40%
   4. D.60%
9. Question 91 mark

   The bacterium used to make curd from milk is

   1. A.Lactobacillus
   2. B.Saccharomyces
   3. C.Aspergillus
   4. D.Rhizobium
10. Question 101 mark

    Which of these is an autoimmune disease?

    1. A.AIDS
    2. B.rheumatoid arthritis
    3. C.typhoid
    4. D.malaria
11. Question 111 mark

    Golden rice is rich in

    1. A.vitamin C
    2. B.β-carotene (provitamin A)
    3. C.iron
    4. D.protein
12. Question 121 mark

    The percentage of photosynthetically active radiation captured by plants is about

    1. A.1–5%
    2. B.10–20%
    3. C.50%
    4. D.90%
13. Question 131 mark

    Assertion (A): Amniocentesis is banned in India for sex determination.

    Reason (R): It is used to detect genetic disorders in the foetus but was misused for female foeticide.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
14. Question 141 mark

    Assertion (A): Restriction enzymes cut DNA at specific palindromic sequences.

    Reason (R): Restriction enzymes are produced by viruses to destroy bacterial DNA.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
15. Question 151 mark

    Assertion (A): Desert plants have sunken stomata.

    Reason (R): Sunken stomata reduce water loss by transpiration.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
16. Question 161 mark

    Assertion (A): Industrial melanism is an example of natural selection.

    Reason (R): In polluted areas, dark moths were less visible to predators and survived better.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.

Section B · Very short answer

1. Question 172 marks

   Give two adaptations of wind-pollinated flowers.

2. Question 182 marks

   What is the role of the placenta? Name two hormones it secretes.

3. Question 192 marks

   What is the role of RNA polymerase and the sigma factor in transcription?

4. OR

   Question 192 marks

   Mention two features of the genetic code.

5. Question 202 marks

   Name the causative organism and one symptom each of (i) ascariasis (ii) ringworm.

6. Question 212 marks

   Differentiate between in situ and ex situ conservation with one example each.

Section C · Short answer

1. Question 223 marks

   Describe the events of the menstrual cycle with the role of hormones.

2. Question 233 marks

   What is a test cross? Explain with an example how it helps determine the genotype of a dominant plant.

3. Question 243 marks

   Describe the experiment of Hershey and Chase. What did it prove?

4. OR

   Question 243 marks

   What is DNA fingerprinting? Give its basis and two applications.

5. Question 253 marks

   How are biogas and microbes related? Describe how a biogas plant works.

6. Question 263 marks

   Explain the steps of gel electrophoresis for separating DNA fragments.

7. Question 273 marks

   Explain the different types of population interactions with one example each of mutualism, parasitism and predation.

8. Question 283 marks

   Explain the theory of natural selection proposed by Darwin.

Section D · Case-based

1. Question 294 marks

   Case study — Gene therapy. In 1990, a four-year-old girl with adenosine deaminase (ADA) deficiency became the first person to receive gene therapy. Her lymphocytes were taken out, a functional ADA gene was introduced into them using a retroviral vector, and the cells were returned to her body. The treatment had to be repeated periodically.

   (i) Which body system is affected by ADA deficiency? (1 mark)

   (ii) What is the role of the retrovirus in this treatment? (1 mark)

   (iii) Why was the treatment not a permanent cure, and how could a permanent cure be achieved? (2 marks)

   OR

   (iii) Name two other applications of biotechnology in medicine. (2 marks)

2. Question 304 marks

   Case study — Ecological succession on bare rock. A volcanic eruption leaves an island covered in bare rock. Over hundreds of years, lichens appear first, then mosses, followed by herbs, shrubs and finally a forest. Ecologists call the final stable community the climax community.

   (i) What is ecological succession? (1 mark)

   (ii) Name the pioneer species on bare rock. (1 mark)

   (iii) Distinguish between primary and secondary succession. Which is faster and why? (2 marks)

   OR

   (iii) How do lichens help in the succession on bare rock? (2 marks)

Section E · Long answer

1. Question 315 marks

   Describe the development of the male gametophyte (pollen grain) in angiosperms. Draw (describe) the structure of a mature pollen grain. Explain one method breeders use to prevent self-pollination.

2. OR

   Question 315 marks

   Describe the process of oogenesis in humans with a schematic (described) representation. How is it different from spermatogenesis?

3. Question 325 marks

   Explain Mendel's law of independent assortment with a dihybrid cross between pea plants with round yellow seeds (RRYY) and wrinkled green seeds (rryy). Give the phenotypic ratio of F₂.

4. Question 335 marks

   What are the causes of drug and alcohol abuse among adolescents? Explain their harmful effects and suggest measures for prevention.

5. OR

   Question 335 marks

   What are the main causes of biodiversity loss ('the evil quartet')? Explain each with an example. Why should we conserve biodiversity?