GCSE-ready- Home
- Lessons
- KS3 Science
- Food webs and ecosystems
Food webs and ecosystems
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
In an ecosystem, living things depend on each other for food, shelter and pollination. A change to one species can affect many others.
Food chains and webs
A food chain shows what eats what. The arrows show the direction energy is transferred.
grass → rabbit → fox
Producers (plants) make food by photosynthesis. Consumers eat other organisms: herbivores eat plants, carnivores eat animals.
A food web shows many linked food chains.
grass → rabbit → fox
Producers (plants) make food by photosynthesis. Consumers eat other organisms: herbivores eat plants, carnivores eat animals.
A food web shows many linked food chains.
Interdependence
Organisms in an ecosystem depend on each other: this is interdependence.
If one population changes, others change too. If foxes are removed, rabbits may increase, then eat so much grass that the grass decreases.
Many crops, such as apples and strawberries, need insects like bees to pollinate them. Without pollinators, we would have much less of this food, so protecting insects matters for human food security.
If one population changes, others change too. If foxes are removed, rabbits may increase, then eat so much grass that the grass decreases.
Many crops, such as apples and strawberries, need insects like bees to pollinate them. Without pollinators, we would have much less of this food, so protecting insects matters for human food security.
Poisons build up
Organisms affect their environment, and the environment affects them.
Some toxic chemicals, like the pesticide DDT, are not broken down or excreted. They build up in an animal's body, and each animal higher up the food chain eats many contaminated organisms.
So the top predators end up with the highest concentration. DDT made the eggshells of birds of prey thin, so fewer chicks survived.
Some toxic chemicals, like the pesticide DDT, are not broken down or excreted. They build up in an animal's body, and each animal higher up the food chain eats many contaminated organisms.
So the top predators end up with the highest concentration. DDT made the eggshells of birds of prey thin, so fewer chicks survived.
In a pond, pike eat perch and perch eat water fleas. Pike are removed. Explain what might happen to the water flea population.
- With no pike eating them, more perch survive.
- More perch eat more water fleas.
- So the number of water fleas falls.
Answer: It may fall, because the perch population grows and eats more water fleas.
Arrows in a food chain show energy transfer. Producers make food; consumers eat other organisms. Organisms are interdependent. Insect pollinators are vital for many crops. Toxic chemicals build up along food chains, reaching the highest levels in top predators.
Check you have got it
Answer 7 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.