IGCSE Biology / Ecosystems
Habitat, population, community, ecosystem revision notes
Edexcel International GCSE Biology (4BI1), chapter 14: Ecosystems, specification point 4.1, 4.5. Free lesson.
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Ecology terms describe living things and their surroundings at different scales. Knowing the difference between them helps you use precise definitions and identify the right factors in exam questions.
How the five terms fit together
These terms describe different levels of organisation. They nest inside each other, from one individual to the living community and its wider environment. Organism: one individual, such as one oak tree or one badger. Population: all the organisms of one species living in the same place at the same time. Community: all the populations of all the species living in that place. It includes living things only. Habitat: the place where an organism lives. Ecosystem: the community, the non-living environment and the interactions between them. Non-living parts include soil, water,…
How biotic and abiotic factors differ
A factor is a part of the environment that can affect organisms. Biotic factors are living or were once living, while abiotic factors are non-living. Check which type a question asks you to name, because the wrong type does not score the mark. Biotic examples include predators, prey, competitors, disease and food supply. Food counts as biotic because it is or was living. Abiotic examples include temperature, light intensity, water, pH and soil type. Oxygen concentration is abiotic, even though living things can affect it. Biotic effects often depend on population size. More predators…
Using the terms for a rock pool
Apply each definition to the place named in the question. A population is one species, a community includes all the living species, and abiotic factors are the non-living parts. In a rock pool, all the limpets together are one population. The community includes the limpets, seaweed, crabs and every other living thing in the pool. Seawater and sunlight are two abiotic factors. Temperature and salinity are other possible examples.
What to remember in an exam
The definitions differ by what they include. A community is all the species living in a place, while an ecosystem adds the non-living parts and interactions. Population means one species. Community means all the species. Ecosystem means the community plus the non-living environment. Habitat means where an organism lives. Biotic means living or once living; abiotic means non-living.