(a) (i) List three components of an ecosystem (ii) Describe briefly the interaction among the components named in (a) (i). (b) List three major steps that a...

(a)(i) Three components of an ecosystem

• Producers (green plants/autotrophs).
• Consumers (herbivores, carnivores, omnivores).
• Decomposers (bacteria and fungi).

(The non-living abiotic component of water, air, soil and light is also part of an ecosystem.)

(a)(ii) Interaction among the components

The producers trap solar energy and manufacture food by photosynthesis. The consumers feed on the producers (and on other consumers), so energy and materials are transferred along food chains and food webs. When producers and consumers die, the decomposers break down their bodies and wastes, releasing mineral nutrients back into the soil and air, which the producers reuse. In this way energy flows through the system and nutrients are recycled among the components.

(b) Three major steps in studying plants and animals in a community

1. Sampling / collection of organisms using suitable methods (quadrat for plants and sedentary animals; pitfall traps, nets or sweep nets for mobile animals).
2. Identification and counting of the organisms collected, and estimation of their abundance/distribution.
3. Recording and analysis of the data (frequency, density, and the physical/abiotic factors measured) to describe the community.

(c) Importance of each factor and its effect on population growth

• (i) Competition: Members compete for limited resources (food, space, light, mates). Intense competition reduces the survival and reproductive rate of the weaker individuals, so it checks and limits population growth.
• (ii) Pathogens: Disease-causing organisms infect members of the population. Outbreaks of disease increase the death rate, thereby reducing the size and slowing the growth of the population.
• (iii) Water: Water is essential for all life processes. An adequate supply promotes survival, reproduction and rapid growth of the population, while a shortage of water raises the death rate and reduces population growth.