The diagram above represents a pyramid of biomass derived from a certain ecosystem
(a) Suggest the type of ecosystem from which the pyramid was derived (1mk)Aquatic ecosystem (b)State the significance of short food chains in an ecosystem (1mk)The shorter the fluid chain, the more energy can be derived from it, hence the larger the population it can support A small boy remarked that his dog looks larger on cold days than on hot days. Give a biological explanation for this (2mks)
Pesticides may kill soil micro-organisms that decompose humus to release mineral salts. In this way they interfere with nutrient cycling. 
Overuse of chemical fertilizers and pesticides have effects on the soil organisms that are similar to human overuse of antibiotics. Indiscriminate use of chemicals might work for a few years, but after awhile, there aren't enough beneficial soil organisms to hold onto the nutrients” (Savonen, 1997).
1. 1989 Q4 P1
State how excessive use of pesticides may affect soil fertility 2. 1989 Q8 P1 The table below shows a list of five human diseases. Complete the table by naming the causative agent of each. The first one has been completed for you. 
Human Diseases
K.C.S.E Biology Q & A - MODEL 2019PP2QN07
Giving examples, describe the following interactions among organisms:
(a) predator-prey (b) symbiosis (c) parasitism. 
answers
​.(a) Predator-Prey
K.C.S.E Biology Q & A - MODEL 2018PP1QN13
State two limitations of using a quadrat to estimate the population of organisms.
ANSWERS
K.C.S.E Biology Q & A - MODEL 2017PP2QN07
Explain the importance of protecting the forest ecosystem with reference to the following:
(a) climate change (b) biodiversity (c) biotechnology (d) water conservation (e) pollution.
answers
a) Climate change
K.C.S.E Biology Q & A - MODEL 2016PP1QN21
​The figure below illustrates a food web in a certain ecosystem.
​From the food web:
(a) Draw the shortest food chain (b) Identify the organism with the highest: (i) number of predators (ii) biomass
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN20
State three factors that contribute to the deceleration phase in the population curve of an organism.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN12
Other than using the quadrant, give two methods of estimating population of grass.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN11
Name two benefits that a parasite derives from the host
answers
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; K.C.S.E Biology Q & A - MODEL 2015PP1QN12
​(a) What is meant by each of the following:
(i) pyramid of biomass? (ii) pyramid of numbers’? (b) During an ecological visit to the Savanna Grassland, students were able to see lions, antelopes, vultures and pastoralists grazing their cattle. Construct a food chain with four consumer levels to illustrate the energy flow in the ecosystem.
answers
(a) (i) Pyramid of biomas represents total dry mass weight of organisms in each trophic level;
(ii) While pyramid of numbers represents the total number of organisms at each trophic level/feeding levels/nutrition levels; 
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