A food chain represents the transfer of material and energy from one organism to another within a habitat. Plants are at the start of every food chain because they make their own food when carbon dioxide reacts with water in the presence of light by a process called photosynthesis. Green plants are known as producers . Other organisms are known as consumers because they obtain energy from the food they eat. Primary consumers feed directly on producers, eg herbivores such as cows, rabbits and caterpillars.
Secondary consumers feed on primary consumers, eg carnivores such as lions ans tigers.
Humans and some other animals are omnivores, ie they eat both producers and consumers. The interdependence of living things can be shown using food chains and webs . Nutrients are constantly being recycled. A system in which these cycles are balanced and self-contained is called an ecosystem . A woodland area, a rainforest or a pond are examples of ecosystems containing several habitats.