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A variety of ecosystems are spread across the world, each with distinctive interacting characteristics and components. Learn about ecosystems.

This lesson includes:

  • two videos to help learn about ecosystems
  • two practise activities to help reinforce learning



An ecosystem describes a natural biological unit that is made up of both living and non-living parts. It is made up of a number of:

  • habitats - the place where an organism lives
  • communities - all the living organisms that live within a habitat

A community can contain a number of different species.

A rock pool on a seashore is described as a habitat and all the organisms that live in it are described as an ecosystem. Watch this film to learn about habitats and ecosystems. You may want to use a pen and paper to make notes.

A look at different habitats and ecosystems

An oak tree can be seen as an ecosystem in which each zone of the tree is a habitat for a distinct community of organisms.


A species is a group of organisms that can interbreed to produce fertile offspring. For example, a horse and a donkey can interbreed with one another but their offspring (a mule) will be unable to reproduce as mules are infertile. The fact that offspring cannot reproduce shows that horses and donkeys belong to two different species.


Biodiversity is the degree of variation that exists among all living organisms on Earth.

When examining the biodiversity on Earth it is useful to consider the populations of organisms in a species. These can fluctuate in an ecosystem depending on factors such as:

  • competition between organisms for resources
  • predator numbers
  • disease

All living things within an ecosystem are interdependent. A change in the size of one population affects all other organisms within the ecosystem. This is shown particularly clearly by the relationship between predator and prey populations.

Predator and prey populations

A predator is an animal that hunts, kills and eats other animals for food. Prey is a term used to describe organisms that predators kill for food.

Watch this film to learn about food chains. Don't forget to take notes.

The energy that all animals get from food begins with the Sun's energy and once it reaches Earth is transferred through food webs and food chains.

Predator/prey relationships can be illustrated in a diagram called a food chain or food web.

A food chain shows the linear flow of energy between organisms

A food web shows the energy flow through interconnected food chains in an ecosystem.

A food web shows the energy flow through interconnected food chains in an ecosystem

Producers make their own food using energy from an abiotic (non-living, physical or chemical) source. For example, plants carry out photosynthesis to make food using light energy from the Sun. Consumers get food from a biotic (living) source by eating the biomass of producers or other consumers.

Within food chains and webs there are organisms that will only consume particular types of food:

  • A herbivore is an organism that only consumes plant material.
  • A carnivore is an organism that only consumes animal material.
  • An omnivore is an organism that will consume both plant and animal material.

There is a continuous struggle between predators and their prey:

  • Predator species need to be adapted for efficient hunting if they are to catch enough food to survive.
  • Prey species must be well adapted to escape predators for their species to continue.

If the prey population in an ecosystem grows, predator numbers will respond to the increased food supply by increasing as well. Growing predator numbers will eventually reduce the food supply to the point where it can no longer sustain the predator population ... and so on.

If an organism is removed from a food chain or web all together, for example due to over-hunting, this can have a catastrophic effect on the other populations in the food web.


Try the activities below to test your knowledge.

Activity 1

Ecosystems quiz

Test how much you know about ecosystems in this quiz.

Activity 2

Predator, prey and populations activity

Have a go at this worksheet from Teachit Science. You can use a paper and pen if you don't have a printer.

Predator, prey and populations activity

There's more to learn

Have a look at these other resources around the BBC and the web.

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