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Biology Paper 2, Nov/Dec 2010  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments

Question 2

(a)(i) What is sexual reproduction? [3 marks]
(ii) Name four organs in mammals that produce sex hormones [4 marks]
(iii) Name one sex hormone produced by each of the organs named in 2(a)(i) [4 marks]

  (b) In a tabular form outline three differences between reproductions in lizards and birds.
[3 marks]

( c) (i) How are identical twins forms in humans? [3 marks]
(ii) State three characteristics features of identical twins.[3 marks]




This question was another popular question in this section and most candidates that answered it performed fairly well. Most candidates who answered the question omitted to say that sexual reproduction was between organisms of the same species. Some candidates wrote it involved fission of gametes rather than fusion of gametes and so lost the score.

In stating organs that produce sex hormones in mammals most candidates could only name two namely testis and ovary and many candidates lost the score for testis because it was wrongly spelt. Most candidates could not state the hormones produced.

Expected answers include:

Testes, ovary, adrenal glands, pituitary gland, placenta

Hormones produced
Testes - Testosterone/Androgens;
Ovary - oestrogen/progesterone
Placenta - progesterone
Adrenal glands - Androgens
Pituitary gland - follicle stimulating
                             Hormone/intersticial cell stimulating

Most candidates could correctly state the differences between reproduction in birds and lizard and tabulated their answers. In answering question 2( c) most candidates could correctly state most of the features of identical twins but could not state how they were formed. Some candidates said they were formed from two fertilized eggs.

Formation ofIdentical twins
- One egg is released from the ovary into the oviduct; and fertilized by a sperm to form a zygote;
- The zygote divides into two embryos; which develop into two identical individuals.

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