SECTION A (40 marks)
Answer all questions in this section on the spaces provided.

1. 1. State four characteristics of fruits dispersed by animals. (4 marks)
      
      
   2. State two roles of each of the following hormones in menstruation:
      
      1. luteinising hormone; (2 marks)
      2. oestrogen. (2 marks)
         
         
2. The diagram below illustrates the role played by red blood cells in transportation carbon (IV) oxide.
   
   
   
   
   1. Other than carbon (IV) oxide transportation in the red blood cells, name the other form of carbon (IV) oxide transportation in humans. (1 mark)
      
      
   2. 1. Name substance F (1 mark)
      2. Name the enzyme marked G and state its role in the reaction. (2 marks)
         Enzyme
         Role
         
         
   3. Explain why transportation of carbon (IV) oxide in red blood cells is advantageous. (2 marks)
      
      
   4. Explain the role of calcium ions in blood clotting. (2 marks)
      
      
3. 1. Describe the mechanism of gaseous exchange in plants through the lenticels. (3 marks)
      
      
   2. Explain each of the following:
      1. the tracheoles lack spiral bands of chitin; (3 marks)
      2. the floor of the mouth is lowered during inhalation in a bony fish. (2 mark)
         
         
4. 1. How is sex determined in man? (4 marks)
      
      
   2. 1. Differenciate between sickle cell anaemia and sickle cell trait. (2 marks)
      2. Explain why people with sickle cell trait have an adaptive survival advantage over normal individuals in malaria endemic regions, (2 marks)
         
         
5. The diagram below represents the transverse section of the spinal cord.
   
   
   
   
   1. Name the part labelled H. (1 mark)
      
      
   2. State two functions of the fluids found in the part labelled J. (2 marks)
      
      
   3. Give a reason for the colour of white matter. (1 mark)
      
      
   4. Name and give the function of the enzyme found at the part labelled K.
      Name (1 mark)
      Function (2 marks)
      
      
   5. On the diagram, use an arrow to show the direction of the impulse transmission along the neurone labelled I. (1 mark)
                                        SECTION B. (40 marks)
                      Answer question 6 (compulsory) and either question 7 or 8 in the spaces provided after question 8.
      
      
6. An experiment was done to determine the uptake of nitrogen from the soil by broad bean seedlings. The experiment was done with one set of seedlings M grown in the atmosphere enriched with carbon (IV) oxide and another set up of seedlings N grown in normal atmosphere.
   
   The amount of nitrogen in each seedling was measured in milligrams at intervals of ten days. The table below shows the results obtained.
   
   
   
   
   1. Using the same axis, draw line graphs of nitrogen uptake by the two (M and N) sets of broad bean seedlings against time. (8 marks)
      
      
      
      
   2. Determine the rate of uptake in Set M between 65 and 85 days. (2 marks)
      
      
   3. 1. What is the relationship between carbon (IV) oxide concentration in the air and nitrogen uptake. (1 mark)
         
         
      2. Account for the relationship in (c) (i) above. (3marks)
         
         
   4. 1. What would happen to the concentration of nitrogen in the seedlings in set M, if after 75 days the seedlings are trasferred to normal atmosphere. (1 mark)
      2. Explain your answer in (d) (i) above. (2 marks)
         
         
   5. State three ways in which nitrogen fixation occurs. (3 marks)
      
      
      
7. 1. Explain how each of the following factors affect the rate of photosynthesis:
      1. temperature; (2 marks)
      2. chlorophyll concentration. (2 marks)
         
         
   2. Describe the process of cabohydrate digestion in human beings. (16 marks)
      
      
      
8. 1. How does excretion take place in plants? (4 marks)
      
      
   2. Describe the role of human skin in homeostasis. (16 marks)