WAEC Biology Question and Solution 3

waec question and solution

WAEC Biology Question and Solution 3

(a) (i) Define the term population.

(ii) List two biotic and abiotic factors each that affect population growth.

(b) What are the effects of food shortage on a population?

(c) Describe two methods each for:

(i) Improving crop yield

(ii) Preserving and storing food. Explain the principle involved in each of the methods described.


Question extracted from June 1988 SSCE Biology 2 Section B Essay Question number 3



(a) (i) The term Population can be defined as the number of a specific species of Organisms living in a particular habitat which have the capability of interbreeding.


In ecology, the population of a particular species in a specific area is evaluated with the help of the Lincoln Index. The area that is used to define a sexual population is defined as the area where inter-breeding is potentially possible between any pair within the area. The probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas. Under normal situations, breeding is significantly more widespread within the area than across the border.


(ii) Two biotic factors that affect population are: (1) Animals (2) Microbes.


(iii) Two abiotic factors that affect population growth are:


(1) Rainfall (2) wind,(3)temperature, (4) Humidity, (5) Soil acidity or alkalinity, (6) Attitude. Any two from the above list would do.


(b) Effects of food shortage on a population are:

(1) Cannibalism — When there is shortage of food in a population, the animals would tend to eat them self. Cannibalism is the eating of one another in the habitat in order to survive. This will in turn lead to reduction of the population.


(2) Competition — Food shortage in a population would as well lead to competition. This is the tendency of organisms in a given population to struggle for the little available food. This situation is referred to as survival of the fittest.


(3) Loss of weight — Food shortage in a population as well result in the loss of weight by individuals which leads to low energy output


4) Disease—Shortage of food can lead to malnutrition which in turn leads to deficiency diseases and reduction in the ability of the organism to resist infection


(5)Death — Shortage of food may lead to starvation which in turn would lead to death of the organism


(6) Famine — when there is food shortage in a population, there is little food available to go round the population which would in turn lead to a severe famine.


(c (i) Two methods of improving crop yield are:

(1) By the application of inorganic manure or fertilizer – Fertilizer ought to be applied before or after planting to boost the fertility of the soil which would in turn lead to an increase in the crop yield. There are different methods of fertilizer application. Fertilizer can be applied through the method of broadcasting, ring method or through the use of the side placement or filial method. Example of fertilizer is NPK- which contains Nitrogen Phosphorus and potassium. You need to make sure that fertilizer does not come into direct contact with growing crops because it would lead to the death of those crops.


(2) Crop rotation — Crop rotation is another method of improving the fertility of the soil and the yield of the crop planted on it.  It is a system of cropping whereby crops are planted on the same piece of land with each crop following the other in a definite sequence during the same planting season. The piece of land may be shared into five plots and different types of crops planted on each of these plots every year in a specific order. To be able to do this effectively, you must make sure that crops that belong to the same family are not permitted to tag along each other in the sequence. Deep rooted crops ought to follow shallow rooted crops and leguminous crops ought to be sowed on the fallow plot in the sequence.


(ii) Methods of food preservation and storage:

(1) Canning — Canning is a method of food storage whereby foods are stored in cans or sealed containers. Before storage, heat treatment is applied to make sure that the food will not be acted upon by microbes and spoil.

(2) Refrigeration — Refrigerator is a good method of food storage because low temperature prevents the growth and spread of microorganisms. Other methods of food storage are:

(3) Drying and salting

(4) Pasteurization,

(5) Additives,

(6) Smoking and

(7) Irradiation.