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. 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. K.C.S.E Biology Q & A - MODEL 2014PP2QN06
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 the normal atmosphere.
The amount of nitrogen in each seedling was measured in milligrams at intervals often days. The table below shows the results obtained.
​(a) Using the same axis draw line graphs of nitrogen uptake by the two (M and N) sets of broad bean seedlings against time.
(b) Determine the rate of uptake of nitrogen in Set M between 65 and 85 days. (c) (i) What is the relationship between carbon (IV) oxide concentration in the air and nitrogen uptake? (ii) Account for the relationship in (c)(i) above. (d) (i) What would happen to the concentration of nitrogen in the seedlings in set M, if after 75 days the seedlings are transferred to a normal atmosphere. (ii) Explain your answer in (d)(i) above. (e) State three ways in which nitrogen fixation occurs.
answers
(c) (i) The higher the carbon UV) oxide content in air, the higher the nitrogen uptake and vice versa;
(ii) More Carbon (IV) oxide in the air makes the seedlings to photosynthesize more; hence more amino acids/protein; are formed in the dark stage; formation of amino acids/protein requires nitrogen; (d) (i) The concentration of nitrogen would remain constant; (ii) Despite decline in CO,; the nitrogen already absorbed/taken up by the plant will still remain: (iii) Lightning; By free-living bacteria/micro organisms; By Rhizobium (in root nodules of legumes); K.C.S.E Biology Q & A - MODEL 2013PP2QN06
A scientist carried out an investigation to find out the population growth of mice under laboratory conditions. Twenty young mice were placed in a cage. The results obtained from the investigation were as shown in the table below.
​(a) On the grid provided, draw a graph of the number of mice against time.
GRAPH PAPER (b) Account for the changes in mice population between (i) O to 2 months (ii) 2 to 6 months (iii) 6 to 10 months (iv) 10 to 12 months. (c) (i) Between which two months was the population change greatest? (ii) Calculate the rate of population change over the period in (c)(i) above. (d) What change in population would be expected if the investigation was continued to the 19th month? (e) To obtain the observed results state two variables that were kept constant during the investigation.
answers
(b) (i) No change in population/population is constant: mice still maturing/have not given birth:
(ii) Slow/gradual population growth; few mice have reached sexual maturity; (iii) Faster/rapid rate of population growth/exponential; Many mice sexually matured/reproducing/enough food/space/no competition birth rate higher than death/no diseases: (iv) Population decline; Competition is high / food is limiting / space is limiting/accumulation of toxic waste/disease (outbreak) deathrate higher than birth rate. (c) (i) 6 and 8; (ii) 310-115 = 195 mice per month; (d) Population would increase; (e) Food; space ; cage size; water; |
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