Communities: An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

The idea

An ecosystem is not just the organisms present; it is the whole system in which a community of living organisms interacts with the non-living parts of the environment. The biotic parts are all the living organisms, including plants, animals, fungi and microorganisms, and their interactions such as feeding, competition and disease. The abiotic parts are the non-living conditions, including light intensity, temperature, moisture, soil pH, mineral content, wind and oxygen availability. These parts interact: plants compete for light and water, animals compete for food and territory, and abiotic factors affect which species can survive.

For example: In a pond, fish, plants and microorganisms interact with water temperature, oxygen concentration and light.

What earns the marks

• Define the community as all the populations of different species living and interacting in a habitat.
• Identify biotic components as living organisms and their interactions, such as predation, competition and disease.
• Identify abiotic components as non-living conditions, such as light, temperature, water, soil pH and oxygen.
• Explain that an ecosystem includes both the community and the abiotic environment, and the interactions between them.
• Give a specific example of an interaction, such as plants competing for light or animals competing for water.
• Recognise that a change in one component, such as reduced rainfall, can affect the whole community.

Common mistakes and how to put them right

• Treating an ecosystem as only the living organisms.

  Put it right by including the abiotic conditions and their interactions.

• Confusing a community with a population.

  Put it right by stating that a community contains multiple species, while a population is one species.

• Listing abiotic factors without linking them to organisms.

  Put it right by explaining how a factor such as temperature affects survival or distribution.

Exam tips

• Use the words biotic and abiotic accurately, and give at least one example of each when explaining an ecosystem.
• When describing an interaction, name both the organisms or factors involved and state the effect on the community.
• Check that your answer covers both the living community and the non-living environment, because the definition requires both.