Students should understand that photosynthetic organisms are the producers of biomass for life on Earth. • Feeding relationships within a community can be represented by food chains. All food chains begin with a producer which synthesises molecules. This is usually a green plant or alga which makes glucose by photosynthesis. • A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem. • Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers. • Consumers that kill and eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles.