Biology Paper 2, WASSCE (PC), 2017

Question 3


  1. (a) Explain briefly the following terms:
    (i) community; [3 marks]
    (ii) population;]
    (iii) ecological niche. [6 marks]
  2. (b) State two reasons why the ecosystem must receive constant supply of energy. [2 marks]
  3. (c) State three likely effects each of:
    (i) the mortality rate being higher than the birth rate within a community. [3 marks]
    (ii) overgrazing on a grassland vegetation. [3 marks]
  4. Explain how cover-cropping aids in the conservation of the soil. [6 marks]

Observation

This was the most popular question answered by candidates. Many candidates were able to answer questions (a), (b) and (c) fairly well. Some candidates could not explain how cover-cropping aids in the conservation of the soil.


The expected answers are:

(a) (ii)Community

Consists of all the populations/different species of living organisms; that exist/live together; in a habitat; and interact with one another.

(ii) Population

Consists of all the organisms; of the same kind/species; living together; in the same habitat.

(iii) Ecological niche
Is the exact place an organism lives; including its behaviour; feeding habit/breeding habits.


(b) Reasons why the ecosystem must receive constant supply of energy

The flow of energy is usually in one unit/direction in a food chain; and some energy is lost as heat; there must be constant supply of energy from outside to keep the ecosystem alive; without it, life would cease.


(c)Effects of:
(i) mortality rate being higher than birth rate

- accumulation/sufficiency/abundance of necessary nutrients;

- reduction in the number of organisms/population;

- extinction of organisms/species with time;

- reduction in competition.

(ii) overgrazing on a grassland vegetation

- reduction of vegetation cover;

- compaction of the soil due to trampling/destruction of soil structure;

- exposure of soil to agents of erosion/water/wind;

- compaction of soil prevents percolation of water into the soil;

- reduction in the activities of soil microorganisms

- destruction of food chains;

- desertification/desert formation.

 

(c) How cover cropping aids in the conservation of soil

Growing of certain crops/grasses/sweet potato/Crotalaria/leguminous plants/legumes; their roots help to hold/bind soil particles together; thus reducing water erosion; their leaves prevent rainfall from directly hitting/pelting the soil surface and loosening it; the leguminous plants improve the soil nitrates; their leaves shade the soil from direct sunlight; therefore reducing evaporation of soil water; prevent leaching of soil nutrients.