Producers, consumers and decomposers

Organisms and their environment · Energy flow, food chains and food webs · note 3 of 3

Spec 19.2.4, 19.2.5, 19.2.6, 19.2.7, 19.2.8, 19.2.9Download all Energy flow, food chains and food webs notes (PDF)Download all notes (PDF)4 pages

Producers, consumers and decomposersSpec 19.2.4, 19.2.5, 19.2.6, 19.2.7, 19.2.8, 19.2.9

In short

A producer is an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis. A consumer gets its energy by feeding on other organisms: herbivores eat plants and carnivores eat other animals. Consumers are primary, secondary, tertiary or quaternary. Decomposers, such as bacteria and fungi, get energy from dead or waste organic material.

Producer: An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis.
Consumer: An organism that gets its energy by feeding on other organisms.
Herbivore: An animal that gets its energy by eating plants.
Carnivore: An animal that gets its energy by eating other animals.
Decomposer: An organism that gets its energy from dead or waste organic material.

Consumers are classed by their position in a food chain.

Classes of consumer
Class	What it eats	Example
Primary consumer	Producers (so it is a herbivore)	Grasshopper
Secondary consumer	Primary consumers (a carnivore)	Frog
Tertiary consumer	Secondary consumers (a carnivore)	Snake
Quaternary consumer	Tertiary consumers (a carnivore)	Eagle

Decomposers, such as bacteria and fungi, feed on dead organisms and waste. They get their energy from dead or waste organic material, and they return nutrients to the soil.

Exam tip:

Learn the definitions word for word. A producer makes its own organic nutrients, usually by photosynthesis. Do not just say that it 'makes its own food'.

Quick check

State the principal source of energy input to biological systems.
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The Sun.
What does a food chain show?
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The transfer of energy from one organism to the next, beginning with a producer.
What is a food web?
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A network of interconnected food chains.
Define a consumer.
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An organism that gets its energy by feeding on other organisms.
Define a decomposer.
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An organism that gets its energy from dead or waste organic material.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

Where does the energy in a food chain come from?

The energy in a food chain comes from the Sun, the principal source of energy input to biological systems. Producers such as green plants and algae absorb light energy and transfer it to chemical energy in organic nutrients by photosynthesis. This chemical energy then passes to consumers when they eat, and to decomposers.

Which way do the arrows go in a food chain?

The arrows in a food chain point from the organism that is eaten to the organism that eats it. They show the direction of energy transfer. So grass → rabbit means the rabbit eats the grass, and energy passes from the grass to the rabbit. Every food chain begins with a producer.

What is the difference between a producer and a consumer?

A producer makes its own organic nutrients, usually using energy from sunlight, through photosynthesis. A consumer gets its energy by feeding on other organisms. Primary consumers are herbivores that eat producers, and secondary, tertiary and quaternary consumers are carnivores. Decomposers are different again: they feed on dead or waste organic material.

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