​Suggest three factors that could have caused the population change between C and D. 

The first one has been completed for you.

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.

Giving examples, describe the following interactions among organisms: 
(a) predator-prey
(b) symbiosis
(c) parasitism.

K.C.S.E Biology Q & A - MODEL 2018PP1QN13

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.

​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 

K.C.S.E Biology Q & A - MODEL 2016PP1QN20

K.C.S.E Biology Q & A - MODEL 2016PP1QN12

K.C.S.E Biology Q & A - MODEL 2016PP1QN11

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? 

​(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.

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.

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.