Population, Community, Habitat and Ecosystem
The four terms — learn them word for word
| Term | Definition | Example |
|---|---|---|
| Habitat | The place where an organism lives | A rocky shore; a hedgerow; the leaf litter of an oak wood |
| Population | All the organisms of one species living in a habitat at one time | All the grey squirrels in a wood |
| Community | All the populations of different species living in a habitat at one time | All the squirrels, oaks, worms, fungi and bacteria in that wood |
| Ecosystem | The community of organisms plus the non-living (abiotic) parts of the area, and the interactions between them | The whole wood: organisms + soil, water, light, temperature |
How they nest inside each other
One species → population.
All the populations together → community (living things only).
Community + abiotic environment → ecosystem.
So an ecosystem is always bigger than a community, because it includes the non-living surroundings.
Wording that earns the mark
- Population: say "all the organisms of one species in a habitat at a given time". The words one species are the mark.
- Community: say "all the populations of different species" — not "all the organisms" and not "all the animals".
- Ecosystem: you must mention both the living community and the abiotic/physical/non-living factors.
Common mistake (examiners flag this every series): writing that a population is "all of the organisms in an area". That is a community. Equally common is defining an ecosystem when the question asked for a community — the community leaves out the soil, water and light.
Quick self-test
- All the dandelions in a field → population
- All the plants, insects and mice in that field → community
- The field including its soil, rainfall and sunlight → ecosystem
- Under a rotting log → habitat
Examiner tip. A common error is to refer to organisms rather than species, and to confuse population with community by saying a population is "all of the organisms". Population = one species; community = all the species; ecosystem = community + abiotic factors. Check which of the three the question actually names before writing.