Biology · Sample Paper 1

General instructions

Section A · Objective

1. Question 11 mark

   The ploidy of the endosperm in angiosperms is

   1. A.n
   2. B.2n
   3. C.3n
   4. D.4n
2. Question 21 mark

   Pollen grains are well preserved as fossils because of

   1. A.intine
   2. B.sporopollenin in the exine
   3. C.cellulose
   4. D.pectin
3. Question 31 mark

   Fertilisation in humans normally takes place in the

   1. A.uterus
   2. B.ampullary region of the oviduct
   3. C.cervix
   4. D.ovary
4. Question 41 mark

   The hormone that triggers ovulation is

   1. A.FSH
   2. B.LH
   3. C.progesterone
   4. D.oxytocin
5. Question 51 mark

   The phenotypic ratio of a monohybrid cross in F₂ is

   1. A.1 : 2 : 1
   2. B.3 : 1
   3. C.9 : 3 : 3 : 1
   4. D.1 : 1
6. Question 61 mark

   A colour-blind man marries a normal (non-carrier) woman. The chance of their son being colour-blind is

   1. A.0%
   2. B.25%
   3. C.50%
   4. D.100%
7. Question 71 mark

   Okazaki fragments are formed on the

   1. A.leading strand
   2. B.lagging strand
   3. C.both strands
   4. D.RNA primer
8. Question 81 mark

   Which codon is the initiation codon?

   1. A.UAA
   2. B.AUG
   3. C.UGA
   4. D.UAG
9. Question 91 mark

   The clot-busting enzyme streptokinase is obtained from

   1. A.Streptococcus
   2. B.Penicillium
   3. C.Trichoderma
   4. D.Monascus
10. Question 101 mark

    Widal test is used to diagnose

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

    EcoRI recognises the sequence

    1. A.GAATTC
    2. B.GGATCC
    3. C.AAGCTT
    4. D.CTGCAG
12. Question 121 mark

    An orchid growing on a mango branch is an example of

    1. A.parasitism
    2. B.commensalism
    3. C.mutualism
    4. D.predation
13. Question 131 mark

    Assertion (A): The pyramid of energy is always upright.

    Reason (R): Energy flow is unidirectional and some energy is lost at each trophic level.

    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): Bt toxin does not harm the bacterium that produces it.

    Reason (R): The toxin exists as an inactive protoxin in the bacterium.

    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): The wings of a bird and of a butterfly are homologous organs.

    Reason (R): They perform the same function.

    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): The Western Ghats are a biodiversity hotspot.

    Reason (R): Hotspots have high species richness and high endemism.

    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

   What is apomixis? Give one advantage of it to farmers.

2. Question 182 marks

   Name two IUDs and state how copper-releasing IUDs prevent pregnancy.

3. Question 192 marks

   Differentiate between active and passive immunity.

4. Question 202 marks

   What are the three steps of PCR? Name the enzyme used.

5. OR

   Question 202 marks

   Why is a selectable marker needed in a cloning vector? Give an example.

6. Question 212 marks

   State Gause's competitive exclusion principle. How can competing species coexist?

Section C · Short answer

1. Question 223 marks

   Draw (or describe) the stages of embryonic development up to implantation in humans.

2. Question 233 marks

   Explain incomplete dominance with an example and the F₂ ratio.

3. Question 243 marks

   Explain the lac operon when lactose is absent and when it is present.

4. Question 253 marks

   Describe the secondary (biological) treatment of sewage.

5. OR

   Question 253 marks

   What are biofertilisers? Give three examples with the role of each.

6. Question 263 marks

   How is human insulin produced by recombinant DNA technology?

7. Question 273 marks

   Describe the steps of decomposition and two factors that affect its rate.

8. Question 283 marks

   Describe the life cycle of Plasmodium in humans. Why does a malaria patient get high fever?

Section D · Case-based

1. Question 294 marks

   Case study — A family pedigree. A couple with normal vision have a son who is colour-blind and a daughter with normal vision. Colour blindness is caused by a recessive allele on the X chromosome.

   (i) Give the genotypes of the parents. (1 mark)

   (ii) Why is colour blindness more common in males? (1 mark)

   (iii) What is the probability that the daughter is a carrier? Show the cross. (2 marks)

   OR

   (iii) Name one other X-linked recessive disorder and its main symptom. (2 marks)

2. Question 304 marks

   Case study — The Nile perch. The Nile perch was introduced into Lake Victoria in East Africa. Within decades, more than 200 species of native cichlid fish became extinct.

   (i) Which cause of biodiversity loss does this show? (1 mark)

   (ii) Name the four causes of biodiversity loss known as the ‘Evil Quartet’. (1 mark)

   (iii) Distinguish between in situ and ex situ conservation with two examples each. (2 marks)

   OR

   (iii) What are sacred groves? Give two examples from India. (2 marks)

Section E · Long answer

1. Question 315 marks

   Describe the structure of a mature embryo sac with a labelled diagram. Explain double fertilisation.

2. Question 325 marks

   Describe the Meselson and Stahl experiment and what it proved.

3. OR

   Question 325 marks

   Describe transcription in bacteria. How is the primary transcript processed in eukaryotes?

4. Question 335 marks

   Explain the Hardy–Weinberg principle. List the five factors that disturb it. In a population, the frequency of the recessive allele is 0.3. Find the frequencies of the three genotypes.

5. OR

   Question 335 marks

   Compare exponential and logistic growth of a population with equations and graphs. Why is the logistic model more realistic?