KCSE BIOLOGY PAPER 2 2011

KCSE BIOLOGY PAPER 2 2011

QUESTIONS

1. The set-up below illustrates a procedure that was carried out in the laboratory with a leaf plucked from a green plant that had been growing in sunlight.
   
   
   1. What was the purpose of the above procedure? (1 mark)
   2. Give reasons for carrying out step A, B and C in this procedure. (3 marks)

(iii) Name the reagent that was used at the step labeled D. (1 mark)

(iv) State the expected result on the leaf after adding the reagent named in (iii) above.

Stain dark blue / Blue dark

1. In humans, hairy ears is controlled by a gene on the Y chromosome.
   1. Using letter Y^H to represent the chromosome carrying the gene for hairy ears, work out a cross between a hairy-eared man and his wife. (4 marks)

   (b) (i) What is the probability of the girls having hairy ears? (1 mark)

   (ii) Give reason for your answer in (b)(i) above. (1 mark)

   (c) Name two disorders in humans that are determined by sex-linked genes. (2 marks)

   (d) Explain how comparative embryology is evidence for organic evolution. (2 marks)

3. (a) Name the causative agent for the following respiratory diseases. (2 marks)

(i) Whooping cough.

(ii) Pneumonia.

(b) Describe how oxygen in the alveolus reaches the red blood cells. (4 marks)

(c) How are the pneumatophores adapted to their function? (2 marks)

4. (a) The diagram below represents a section of the human brain.

1. Name the structures labeled P and R.
2. State two functions of the part labeled Q.

(b) (i) Name two reproductive hormones secreted by the pituitary gland in women. (2 marks)

(ii) State one function of each of the hormones named in (b)(i) above. (2 marks)

5. (a) The diagram below represents a flower.

(i) On the diagram, name two structures where meiosis occurs. (2 marks)

………………………………………………………………………………………………………..

………………………………………………………………………………………………………

(ii) How is the flower adapted to prevent self-pollination?

(b) The diagram below represents a human reproductive organ.

(i) Explain two adaptations of the structure labeled L to its functions. (2 marks)

Explain the role of gland labeled K.

SECTION B (40 MARKS)

Answer 6 (compulsory) and either question 7 or 8 in the spaces provided after question 8.

6. (a) An experiment was carried out to investigate the population of a certain micro-organism. Two petri-dishes were used. Into the petri-dish labeled M, 60 cm³ of a culture medium was placed while 30 cm³ of the same culture medium was placed in petri-dish labeled N. Equal numbers of the micro-organisms were introduced in both petri-dishes. The set-ups were then incubated at 35⁰C. The number of micro-organisms in each petri-dish was determined at irregular intervals for a period of 60 hours. The results were as shown in the table below.

1. On the same axes, draw the graphs of relative number of micro-organisms against time on the grid provided. (7 marks)

(ii) After how many hours was the difference between the two populations greatest? (1 mark)

(iii) Work out the difference between the two populations at 50 hours. (2 marks)

1. 1. With a reason, state the effect on the population of micro-organisms in petri-dish M if the temperature was raised to 60⁰C after 20 hours. (2 marks)

(v) Account for the shape of the curve for population in petri-dish N between 46 hours and 59 hours. (3 marks)

(b) Explain how osmotic pressure in the human blood is maintained at normal level. (5 marks)

When the osmotic pressure of the blood increases beyond the normal level, osmoreceptors in the hypothalamus detect this and stimulate the pituitary gland to secrete more ADH (vasopressin), which makes kidney tubules more permeable to water. More water is reabsorbed into the blood, reducing the osmotic pressure to the normal level.

When osmotic pressure falls below the normal level, the osmoreceptors in the hypothalamus detect this and the pituitary gland is less stimulated. The kidney tubules become less permeable to water, hence less water is absorbed into the blood, increasing the osmotic level.

When osmotic pressure is high:

When there is too much Na⁺_(aq) in the blood, the adrenal cortex responds by secreting less aldosterone, which causes less Na⁺_(aq) to be absorbed from the kidney tubules into the blood, lowering the sodium ion level.

When osmotic pressure is low:

When there is too low Na⁺ ions or Na⁺_(aq) in the blood, the adrenal cortex responds by secreting more aldosterone, which causes more Na⁺ to be reabsorbed from the kidney tubules into the blood, raising the Na⁺ level.

7. (a) Explain how structural features in terrestrial plants affect their rate of transpiration. (13 marks)

(b) Explain how the human skin brings about cooling of the body on a hot day. (7 marks)

8. (a) Describe the exoskeleton and its functions in insects. (13 marks)

1. Describe how accommodation in the human eye is brought about when focusing on a near object. (7 marks)