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BiologyGCSEAQA & EdexcelYears 10–11

GCSE Biology Ecology Notes

Ecology studies how living things interact with each other and their environment. Human activity is now a major threat to biodiversity.

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Key concepts

Ecosystem
A community of organisms (biotic) interacting with their non-living (abiotic) environment.
Interdependence
Organisms in a community depend on each other for food, shelter, pollination and seed dispersal.
Biodiversity
The variety of species in an ecosystem. High biodiversity means a more stable, resilient community.
Carbon cycle
Photosynthesis removes CO₂; respiration, combustion and decomposition return it.
  • Biotic factors: predators, food supply, disease, competition. Abiotic: light, temperature, water, pH, minerals.
  • Deforestation and burning fossil fuels increase atmospheric CO₂ and reduce biodiversity.
  • The water cycle: evaporation → condensation → precipitation → surface runoff/groundwater.

Worked example

Explain how deforestation contributes to global warming.

  1. 1Trees photosynthesise, removing CO₂ from the atmosphere.
  2. 2Cutting down trees means less CO₂ is absorbed.
  3. 3Burning the felled wood releases stored carbon as CO₂.
  4. 4More atmospheric CO₂ enhances the greenhouse effect and warms the planet.

Answer: Less photosynthesis + more combustion → more CO₂ → enhanced greenhouse effect.

Common mistakes

✗ Confusing biotic and abiotic factors.

✓ Biotic = living (predators, disease); abiotic = physical (light, temperature, pH).

✗ Saying 'the water cycle produces water'.

✓ The water cycle recycles existing water between reservoirs — no new water is made.

✗ Missing decomposers in the carbon cycle.

✓ Decomposers respire, releasing CO₂ from dead material back to the atmosphere.

Quick check

Try these, then reveal the answers.

Name two abiotic factors.Reveal answer

Light intensity and temperature (also water, pH, minerals).

Which processes add CO₂ to the atmosphere?Reveal answer

Respiration, combustion and decomposition.

Why is high biodiversity a benefit?Reveal answer

It makes ecosystems more stable and resilient to change.

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Exam tips

  • Learn the carbon and water cycles as flow diagrams — label every process and reservoir.
  • For sampling questions, describe random quadrats and use mean per m² × area for population estimates.
  • When discussing human impact, cover both cause and consequence with a linking word ('so', 'therefore').

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Key terms explained

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What is active transport?What is diffusion?What is dna?What is enzyme?What is homeostasis?What is mitosis?Full glossary

Frequently asked questions

What is meant by interdependence?+

Organisms in a community rely on each other for food, shelter, pollination and seed dispersal, so a change in one species affects many others.

How do humans reduce biodiversity?+

By destroying habitats (deforestation, farming), polluting land, water and air and causing climate change through greenhouse gas emissions.

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