Life on Earth, in levels: The biosphere is one huge ecological system. It is built from individuals, populations, communities and ecosystems.
The points to remember
- The biosphere is all the parts of the Earth where life exists.
- It is an ecological system made of four levels.
- Individual: one organism.
- Population: all the organisms of one species in an area, able to breed together.
- Community: all the populations living and interacting in an area.
- Ecosystem: a community plus its non-living surroundings.
Remember it as: One, one kind, all kinds, add the non-living: individual, population, community, ecosystem.
Real example: about 3000 lions live in the Serengeti in Tanzania. One lioness is an individual; all the lions together are a population.
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The two levels people mix up most are community and ecosystem. The difference is the abiotic parts.
Telling the levels apart
- Population = one species. Community = many species.
- A community is living things only.
- An ecosystem adds the abiotic parts: water, soil, light, temperature.
- Each level sits inside the next: individual, population, community, ecosystem, biosphere.
- Name the place and the species to make each level clear.
Community
- Living things only.
- Many populations, interacting.
Ecosystem
- The community plus the non-living parts.
- Water, soil, light, temperature.
Two common slips: A population is one species, not 'all the animals'. A community has no non-living parts: rocks and water belong to the ecosystem.
Real example: in Lake Victoria, all the Nile perch form one population; the perch, other fish, snails and water plants form the community; add the water, mud and sunlight and you have the ecosystem.
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How this comes up: The levels are asked as short definitions in Paper 2 Section A, or as an outline with a named example [4].
The Serengeti National Park in Tanzania is home to lions, zebras, grasses and acacia trees, on grassland with a long dry season.
Outline the levels of ecological organisation in the biosphere, with reference to the Serengeti.
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