An ecosystem is the interaction of a community of living organisms…

The idea

An ecosystem is not just a place or a list of species; it is the interaction between the living community and the non-living surroundings. The biotic part is all the organisms: plants, animals, fungi and bacteria, including their relationships such as feeding, pollination and decomposition. The abiotic part is everything non-living: light intensity, temperature, moisture, soil pH and mineral content, wind and oxygen availability. These parts interact constantly. For example, in a pond, water temperature and oxygen concentration (abiotic) affect which fish and plants (biotic) can survive, while the plants add oxygen and the fish release carbon dioxide. Changes to one part ripple through the whole system: a drought lowers water availability, reducing plant growth, which reduces food for herbivores. Always name both components and state how they affect each other.

What earns the marks

• Define the biotic component as the community of living organisms, including their interactions.
• Define the abiotic component as the non-living parts of the environment, such as light, temperature, water, soil pH and oxygen.
• State that an ecosystem involves interaction between the biotic and abiotic components, not merely their coexistence.
• Give a named example of an interaction, such as plants affecting oxygen concentration or temperature affecting which species survive.
• Explain that a change in one component can affect other components of the ecosystem.

Common mistakes and how to put them right

• Defining an ecosystem as only the organisms present.

  Put it right: It also includes the non-living environment and the interactions between them.

• Treating abiotic factors as unimportant background.

  Put it right: Factors such as temperature and light directly affect which organisms survive.

• Giving a habitat as the definition of an ecosystem.

  Put it right: A habitat is where an organism lives, whereas an ecosystem includes the community and its interactions with the abiotic environment.

Exam tips

• In definitions, include both the living community and the non-living environment, and use the words biotic and abiotic.
• When giving an example, state the direction of the effect, such as how temperature affects enzyme activity or growth.
• Avoid writing that an ecosystem is just a habitat; add the idea of interaction.