(a) What is a habitat? (b) Describe the energy flow in a freshwater habitat. (c) List (i) three biotic factors; (ii) five abiotic factors which affect plant...

(a) What is a habitat?

A habitat is the particular place or type of environment in which an organism naturally lives, feeds and reproduces, and which provides all the conditions and resources it needs for survival. Examples are a pond, a forest floor and the seashore.

(b) Energy flow in a freshwater habitat

Energy enters the freshwater habitat as sunlight, which is trapped by the producers (green plants such as algae, Spirogyra and water weeds) during photosynthesis and stored as chemical energy in food. This energy then flows along a food chain from one feeding level (trophic level) to the next:

\[ \text{Sun} \rightarrow \text{Producers} \rightarrow \text{Primary consumers} \rightarrow \text{Secondary consumers} \rightarrow \text{Tertiary consumers} \]

For example: algae \(\rightarrow\) water flea \(\rightarrow\) small fish \(\rightarrow\) big fish. The primary consumers (herbivores such as tadpoles and water fleas) eat the producers; secondary consumers (small carnivorous fish) eat the herbivores; and tertiary consumers (larger fish) eat the smaller fish. At each transfer, much of the energy is lost as heat during respiration and in movement, so the amount of usable energy decreases along the chain. When plants and animals die, decomposers (bacteria and fungi) break down their bodies, releasing the remaining energy as heat and returning nutrients to the water. Energy flow is therefore one-way (non-cyclic).

(c)(i) Three biotic factors affecting plants in a freshwater habitat

1. Grazing/feeding by aquatic animals (herbivores).
2. Competition among plants for light and space.
3. Decomposers (bacteria and fungi) acting on dead plants.

Also: disease-causing organisms (parasites).

(c)(ii) Five abiotic factors affecting plants in a freshwater habitat

1. Light (intensity and penetration).
2. Temperature of the water.
3. Dissolved oxygen and carbon dioxide.
4. Dissolved mineral salts (nutrients).
5. pH (acidity or alkalinity) of the water.

Also: water current and turbidity.