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.

K.C.S.E Biology Q & A - MODEL 2012PP2QN08

The data provided below represent populations of a predator and its prey over a fifty years’period.

​(a) (i) Using the same axes, draw graphs of the relative populations of P and Q against time. 
(ii) With a reason, identify the curve that represents the prey. 
(iii) Account for the two populations between 25 arid 32 years. 
(iv) Which years were the two populations equal? 
(v) A part from predation, state three biotic factors that may have led to the decline of the prey population. 
(b) Describe the hazards of air pollution by Sulphur (IV) Oxide. 

K.C.S.E Biology Q & A - MODEL 2012PP1QN21

The table below shows results of a study of three plants C, D and E growing in different habitats.

(a) Which one of the plants C, D and E grows in an area of relatively low water availability? 
(b) Explain your answer in (i) above. 

 An experiment was carried out to investigate the population of a certain micro-organism. Two petri-dishes were used. Into the petri-dish label led M, 60cm3 of a culture medium was placed while 30cm3 of the same culture medium was placed in petri-dish labelled N. Equal numbers of the micro-organisms were introduced in both petri-dishes. The set-ups were then incubated at 35°C. The number of micro-organisms in each petri-dish was determined at irregular intervals for a period of 60 hours. The results were as shown in the table below.

(i)On the same axes, draw the graphs of relative number of micro-organisms against time on the grid provided. 
(ii) After how many hours was the difference between the two populations greatest? 
(iii) Work out the difference between the two populations at 50 hours. 
(iv) With a reason state the effect on the population of micro-organisms in petri-dish M if the temperature was raised to 60°C after 20 hours. 
(v) Account for the shape of the curve for population in petri-dish N between 46 hours and 59 hours.