K.C.S.E Biology Q & A - MODEL 1996PP1QN 20

K.C.S.E Biology Q & A - MODEL 1996PP1QN 20

A culture of bacteria was incubated in nutrient agar at 350C. Samples were taken at intervals in order to estimate the number of bacteria in the population. The data obtained is shown in the graph below.

​(a) When was the pollution of bacteria 350 million
(b) Account for the shape of the  graph between
        (i) A and B
        (ii) B and C
        (iii) C and D
(c) Give three reasons  for  the shape of the  curve between D and E
(d) (i) Suggest what would happen to the population of the bacteria if the temperature was  lowered to 00 after incubating for 12 hours.
        (ii) Give a reason for your answer in (d) (i) above
(e) Give three reasons why it is important to  control human population growth rate  in Kenya?

ANSWERS

​(a) 10 HRC and 31 HRC 
(b) (i) A and B The number of bacteria  dividing are  few: bacteria  are adjusting conditions: few are dying therefore  high increase in population
      (ii) B and C More cells are dividing due to suitable environment/  favorable conditions; few are  dying; therefore high  increase in population
      (iii) C and D No population change; number produced is equal to number dying.
(c) Accumulation of toxic wastes; that kills bacteria; depletion of nutrients leading to competition of  space.
(d) (i) The population will remain the same
    (ii) Temperature not conclusive for division
(e)  Food to be  sufficient for population
    Social amenities/ education; health services