FORM SIX BIOLOGY NECTA 2012

THE UNITED REPUBLIC OF TANZANIA NATIONAL EXAMINATIONS COUNCIL
ADVANCED CERTIFICATE OF SECONDARY EDUCATION
EXAMINATION

133/2 BIOLOGY 2

For Both School and Private Candidates)

Time: 3 Hours Thursady, 16th February 2012 p.m.

Instructions

1. This paper consists of eight (8) questions in sections A. B. C and D. 

2. Answer five questions by choosing at least one (I) question from each section. 

3. Each question carries twenty (20) marks.

4. Except for diagrams that must be drawn in pencil, all writing should be in blue or black ink. 

5. Cellular phones are not allowed in the examination room.

6. Write your Examination Number on every page of your answer booklet(s).

SECTION A

1.(a) Explain the general characteristics of viruses.

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(b) Give reasons to justify the class in which spider belongs.

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2.(a) Some fungi are useful and others are detrimental to man. Explain this fact and give one example in each case.

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(b) Explain how a saprophytic organism is adapted to its mode of nutrition.

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SECTION B

3. With reference to the first and second Mendel's laws describe how the ratios of 3:1 and 1:1 in a monohybrid cross; 9:3:3:1 and 1:1:1:1 in a dihybrid cross are obtained.

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4. (a) Describe the advantages of applying genetic engineering in plant and animal breeding.

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(b) Explain why farmers are not advised to plant hybrid seeds such as tomatoes from one season to another.

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SECTION C

5. (a) Explain how feedback system works to bring about homeostatic conditions in animals.

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(b) Describe the counter current multiplier system in the loop of Henle.

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6. Describe the population growth shown in a sigmoid and J-shaped growth curves.

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(b) Explain the causes of a step-like growth pattern in arthropod.

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SECTION D

7. (a) Describe three observations and two deductions of Darwin's theory of natural selection.

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(b) A researcher sprayed DDT regularly for several years to a population of pests. He sampled the population in every year of spraying. When the results were graphically represented the graph obtained was as shown in Figure 1.

Fig. 1

Explain this observation in terms of natural selection.

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8. (a) Discuss how smoke and sulphur dioxide in the polluted atmospheric air (troposphere) affects living organisms.

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(b)Explain any six importance of conserving forest in the ecosystem.

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