​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.

 In an experiment, students treated seedlings as illustrated below.

​(i) Account for the observations made in seedling I. 
(ii) Explain the similarity in the end results made in seedlings II and III. 
(iii) State the likely treatment that would make seedlings II and III respond like seedling I.

In an experiment to investigate the effect of sodium chloride on the growth rate in a spinach seedling, seeds were treated with different concentrations of sodium chloride. The results are as recorded in the table below.

​(a) From the results in the table above, explain the effect of increasing the concentration of sodium chloride. 
(b) Apart from a ruler, state two other equipment one would need to determine the rate of growth in the roots. 
(c) With a reason, state one other part of the seedling the students would focus on to determine the effect of sodium chloride on growth. 
(d) State the likely effect on the seedling of increasing the concentration of sodium chloride to 2.20mol/l

K.C.S.E Biology Q & A - MODEL 2019PP1QN16

 A female human being was found to have an extra sex chromosome in her cells.

​(a) Give the total number of chromosomes in the female individual’s cells. 
(b) Explain the possible cause of this condition. 
(c) State two physical characteristics observed in the female individual with such a condition.

K.C.S.E Biology Q & A - MODEL 2018PP2QN07

K.C.S.E Biology Q & A - MODEL 2018PP2QN07

The effect of auxin concentration on growth response of two parts of a plant, X and Y was investigated over a period of time. The results were tabulated as shown in the table below.

(a) On the same axis, draw line graphs of the effect on growth of the two parts, X and Y (percentage inhibition or stimulation) against the concentration 
(b) With reasons, name the two parts of the plant, X and Y.
X 
Reason 
Y
Reason
(c) From the graph identify: .
(i) the point at which the percentage stimulation was the same for both X and Y. 
(ii) the optimum concentration of auxins required for part Y 
(d) State three ways in which the effects of auxins on plants is applied in flower farming.
(e) Distinguish between simple and conditioned reflex action 

Below is a graphical representation of students’ height in a classroom.

​(a) Name the type of curve illustrated. 
(b) (i) State the type of variation represented by the curve. 
(ii) State two meiotic processes that lead to variation among organisms. 
(iii) Explain the role of variation in organisms. 
(c) Explain the need for genetic counselling in present day health facilities.

State two characteristics of living things illustrated in the photograph below.

The diagram below illustrates a germinating seedling.

​(a) Name the type of germination illustrated in the diagram
 (b) Describe how the type of germination named in (a) above is brought about.