(a) (i) What is a habitat? (ii) Explain briefly three roles of a decomposer in an ecosystem. (b) Explain briefly energy flow in a freshwater habitat. (c) (i...

(a)(i) What is a habitat?

A habitat is the natural place or environment where an organism (plant or animal) lives, feeds and reproduces, for example a pond, a forest or the soil.

(a)(ii) Three roles of a decomposer in an ecosystem

• It breaks down dead plants and animals and other organic waste, so it clears the environment of dead matter.
• It releases (recycles) mineral nutrients such as nitrogen and carbon back into the soil, water and air for reuse by plants.
• It keeps the nutrient cycles going, so producers can continue to obtain the raw materials they need.

(b) Energy flow in a freshwater habitat

Energy from the Sun is trapped by producers (green water plants and algae/phytoplankton) during photosynthesis and stored as chemical energy in their food. This energy passes to primary consumers (herbivores such as water fleas and small fish) when they eat the plants, and then to secondary and tertiary consumers (larger fish and birds) along the food chain. At each transfer (trophic level) much of the energy is lost as heat during respiration and in undigested waste, so less energy is available at each higher level. Decomposers finally break down all dead organisms and release the remaining energy as heat. Energy therefore flows in one direction only, from the Sun through the organisms and out as heat, and is not recycled.

(c)(i) Three harmful effects of microorganisms to plants

1. They cause plant diseases such as leaf spot, blight and wilt.
2. They cause rotting and spoilage of fruits, tubers and stored produce.
3. They cause galls or decay that reduce crop yield.

(c)(ii) Six beneficial effects of microorganisms to humans

1. They decay dead matter and recycle nutrients, keeping the environment clean.
2. They fix atmospheric nitrogen, enriching the soil for crops.
3. They are used in making foods such as bread, yoghurt, cheese and local drinks (fermentation).
4. They are used to produce antibiotics such as penicillin.
5. Bacteria in the gut help in digestion and make some vitamins.
6. They are used in sewage treatment and in producing alcohol and other industrial products.