K.C.S.E Biology Q & A - MODEL 2015PP2QN06

K.C.S.E Biology Q & A - MODEL 2015PP2QN06

The graph below shows the relative numbers of three main species of organisms in a pond.

​(a) Giving a reason for your answer, which of the species is a
(i)  producer?
 Reason 
(ii) secondary consumer? 
 Reason 
(b) State the depths at which each of the populations labelled L, M and N is at its optimum.
L
M
N  

(c) (i) Which method may have been used to determine the population of organisms labelled N in the pond? 
(ii) Give a reason for your answer in (c) (j) above. 
(iii) State the assumptions made when using the method in (c) (i) above. 
(d) State two reasons why primary productivity in the pond decreases with depth. 
(e) Explain the ecological importance of fungi to plants.
(f) Why is flooding likely to lead to a cholera outbreak? 

ANSWERS

​(a) (i) Producer - M 
Reason Largest in number hence source of food for the other species
Abundant on the water surface to trap light for photosynthesis;
(ii) Secondary consumer - N 
Reason - Smaller in number than L and M 
(b) L -1.125m;
M- 0.75m;
N- 2.00m;  
(c) (i) Capture - Recapture (method) /Capture - mark - release - recapture; 
(ii) Animals are highly mobile; 
(iii) No migration during the period of survey/study;
No deaths/variation/reproductiori in population during the period;
 Method of marking does not affect the animal behaviour;
 Marked/released animals will freely mix with others in the pond;
 Released/marked animals will have enough time to mix with the others;
 There is uniform/random distribution of animals within the period.
(d) Decrease in light intensity as depth increases; 
Decrease in temperature as depth increases; 
(e) Breakdown of organic materials/decompose/rot/decay of materials; to release plant nutrients; 
(f) Flood water may mix with human waste contaminated with cholera bacteria; The flood water may then contaminate food / water sources; The contaminated water/food causes cholera infection when ingested;