A food chain represents the feeding relationships within a community. All food chains begin with a producer, usually a green plant or alga, which makes glucose by photosynthesis. Primary consumers eat the producer, secondary consumers eat the primary consumers, and tertiary consumers eat the secondary consumers. Consumers that kill and eat other animals are predators, and those eaten are prey.
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.
Feeding levels in a food chain
Name
What it does
Example
Producer
Makes glucose by photosynthesis
Grass
Primary consumer
Eats the producer
Grasshopper
Secondary consumer
Eats the primary consumer
Frog
Tertiary consumer
Eats the secondary consumer
Snake
Consumers that kill and eat other animals are predators, and those eaten are prey.
Arrows in a food chain point from the food to the animal that eats it. Grass → rabbit means the rabbit eats the grass.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026
Frequently asked questions
How does carbon move through the carbon cycle?
Carbon moves through the carbon cycle when plants and algae take in carbon dioxide for photosynthesis, then carbon passes along food chains as animals feed. Plants, animals and microorganisms release carbon dioxide back into the atmosphere by respiration. When organisms die, microorganisms decompose them and release carbon dioxide by respiration, so carbon is available for new organisms.
How do you use a quadrat to estimate population size?
To estimate population size, place a quadrat at random positions, using random coordinates to avoid bias, and count the organisms of the species inside it each time. Repeat many times, for example 10 or more quadrats, and calculate the mean number per m². Then multiply the mean per m² by the total area of the habitat in m².
Why do predator and prey populations rise and fall in cycles?
Predator and prey numbers rise and fall in cycles because predator numbers depend on their food supply. When prey are plentiful, predators eat more and breed, so their numbers rise. More prey are then eaten, so prey numbers fall. With less food, predator numbers fall too, fewer prey are eaten, and prey numbers rise again.
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