Food chains

A food chain shows what eats what in a habitat, and how energy passes from one organism to the next. Almost all of that energy starts as light from the Sun, captured by plants.

The arrows point to the eater. They show which way the energy goes: from the food to the animal that eats it. “grass → grasshopper” means the grasshopper eats the grass.

Word	Meaning	Example
Producer	Makes its own food by photosynthesis. Every food chain starts with one.	Grass, oak trees, algae
Consumer	Gets its energy by eating other organisms	Every animal
Primary consumer	Eats the producer	Grasshopper
Secondary consumer	Eats the primary consumer	Frog
Tertiary consumer	Eats the secondary consumer	Heron
Herbivore, carnivore, omnivore	Eats plants; eats animals; eats both	Rabbit; stoat; badger
Predator and prey	A predator hunts and kills other animals, its prey	Owl and mouse
Top predator	At the end of its food chain. An apex predator has no natural predators at all.	Harpy eagle
Decomposer	Breaks down dead material and waste	Bacteria, fungi

Energy is lost at every step, through movement, keeping warm (heat from respiration) and waste such as droppings. Only a small part of the energy at one level reaches the next. So food chains rarely have more than four or five links, and there are fewer animals at each level going up.

Decomposers (bacteria and fungi) feed on dead plants, dead animals and waste. They release the minerals in them, such as nitrates, back into the soil for plants to take up, and give out carbon dioxide as they respire. Earthworms and woodlice help by breaking dead leaves into small pieces. Without decomposers, dead things would pile up and plants would run short of minerals.

Stretch A pyramid of numbers shows how many organisms there are at each level of a food chain. It is not always pyramid-shaped: one oak tree can feed 2000 caterpillars. A pyramid of biomass shows the total mass at each level and is almost always pyramid-shaped.