(a) Distinguish between an ecosystem and a food chain (b) Explain the interdependence of the biotic and abiotic components of the environment

(a) Distinction between an ecosystem and a food chain

An ecosystem is a natural unit made up of all the living organisms (biotic components) of an area together with the non-living environment (abiotic components) such as soil, water, air, sunlight and climate, and the interactions and energy flow between them (for example a pond, forest or grassland).

A food chain is much narrower: it is a single line of feeding relationships showing the transfer of energy and nutrients from one organism to the next as one feeds on another, for example: grass \(\rightarrow\) grasshopper \(\rightarrow\) lizard \(\rightarrow\) hawk. A food chain is therefore only one part of the wider ecosystem.

(b) Interdependence of the biotic and abiotic components

• Green plants (producers) depend on abiotic factors, using sunlight, carbon dioxide, water and soil nutrients to manufacture food through photosynthesis.
• Animals (consumers) depend on plants and on other animals for food, and on the abiotic environment for oxygen, water and shelter.
• Decomposers (bacteria and fungi) break down dead plants and animals, returning mineral nutrients to the soil, water and air, which the plants then reuse; this recycles nutrients.
• In turn the biotic components affect the abiotic environment: plants add oxygen and humus, give shade and reduce erosion, while animal respiration returns carbon dioxide.
• Thus a change in one component (for example loss of vegetation or reduced rainfall) upsets the others, showing that biotic and abiotic parts form a single, balanced, interdependent system through cycles of energy and matter.