A community and the non-living components of its environment together form…

The idea

An ecosystem is the community plus the abiotic components of its environment, working as one interacting unit. Abiotic components are non-living, physical and chemical conditions: light intensity, temperature, water availability, pH, oxygen and carbon dioxide concentration, soil type and wind exposure. Two things link the living and non-living parts. Energy flows one way: light is captured by producers, passes along food chains and is lost as heat at every transfer, so the system needs a constant input. Nutrients such as carbon and nitrogen cycle repeatedly between the abiotic reservoir, producers, consumers and saprobionts.

What earns the marks

• An ecosystem being a community, or all the populations, together with the non-living or abiotic components of the environment.
• Naming a correct abiotic factor such as light intensity, temperature, pH, water availability or mineral ion concentration.
• Stating that the biotic and abiotic parts interact.
• Energy flowing through the ecosystem while nutrients are cycled between organisms and the abiotic environment.
• Stating that abiotic conditions determine which species can survive in that ecosystem.

Common mistakes and how to put them right

• Naming predators, competitors or pathogens as abiotic factors.

• Writing the vague phrase the environment instead of the non-living components of the environment.

• Stating that nutrients flow through and energy is recycled, which reverses both.

• Listing soil or water as members of the community.

• Using habitat and ecosystem as if they were the same term.

Exam tips

• Learn the exact terminology for fill-the-gap questions, as precise wording is required.
• Name a specific abiotic factor such as light intensity rather than a vague one such as weather.
• If a question asks how a factor affects an ecosystem, follow it through to a named population.