Who eats whom?
Every living thing needs energy. That energy starts with the Sun and passes from one living thing to the next when one eats another. A food chain shows this path.
grass → grasshopper → frog → snake → hawk
The arrows mean "is eaten by" and show the direction energy flows.
Producers
A producer makes its own food. Plants, algae and some bacteria use sunlight to make sugar in a process called photosynthesis. Every food chain starts with a producer.
Consumers
A consumer eats other living things to get energy.
| Type | What it eats | Examples |
|---|---|---|
| Herbivore | Only plants | Rabbit, deer, caterpillar |
| Carnivore | Only animals | Lion, shark, owl |
| Omnivore | Plants and animals | Bear, raccoon, people |
| Scavenger | Dead animals | Vulture, crow |
Consumers are also named by their place in the chain:
- Primary consumers eat producers (grasshopper).
- Secondary consumers eat primary consumers (frog).
- Tertiary consumers eat secondary consumers (snake).
- The top predator has no natural predators (hawk).
Decomposers
A decomposer breaks down dead plants, dead animals and wastes. Mushrooms, bacteria and worms are decomposers. They return nutrients to the soil, so producers can use them again. Decomposers are nature’s recyclers.
Food webs
In real life, most animals eat more than one thing, and most are eaten by more than one predator. A food web shows many food chains connected together.
In a forest food web:
- Mice eat seeds and insects.
- Owls, foxes and snakes all eat mice.
- Foxes also eat rabbits and berries.
A food web shows that if one living thing disappears, many others may be affected.
Energy is lost at each step
Only a small part of the energy, about 10%, passes from one level to the next. The rest is used for moving, breathing and staying warm, or is lost as heat. That’s why food chains rarely have more than four or five links, and why there are far fewer hawks than grasshoppers.
| Level | Example | Energy available |
|---|---|---|
| Producer | Grass | 10 000 units |
| Primary consumer | Grasshopper | 1000 units |
| Secondary consumer | Frog | 100 units |
| Tertiary consumer | Snake | 10 units |
What happens if something changes?
Imagine a disease kills most of the frogs.
- Grasshoppers have fewer predators, so their numbers grow.
- With more grasshoppers, more grass gets eaten.
- Snakes have less food, so their numbers fall.
- Hawks may have to find other food.
Ocean food chains
phytoplankton (tiny algae) → zooplankton → small fish → tuna → shark
Phytoplankton are tiny producers that drift in the ocean. They make much of the oxygen we breathe!
Common mistakes
- Drawing arrows the wrong way. Arrows point toward the eater, showing where energy goes.
- Starting a food chain with an animal. Food chains start with a producer.
- Forgetting decomposers.
Try it yourself
- Write a food chain from your own lunch. (Example: wheat → bread → you.)
- Draw a food web with these living things: grass, rabbit, mouse, fox, owl, seeds, hawk.
- Predict what would happen to your web if all the rabbits disappeared.
Quick recap
- Food chains show how energy passes from one living thing to another.
- Every chain starts with a producer that gets energy from the Sun.
- Consumers can be herbivores, carnivores or omnivores.
- Decomposers recycle nutrients.
- Food webs connect many food chains; a change to one part affects others.