Ecology
Ecosystems and interdependence, sampling and quadrats, cycling of materials, and human impacts on biodiversity.
Learn
Ecology, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe ecosystems and the interdependence of organisms
An ecosystem is the living community together with its non-living surroundings. Organisms depend on each other for food, shelter, pollination and seed dispersal, so a change to one species ripples through the rest - this is interdependence. A stable community is one where the populations stay roughly steady over time.
Explain how abiotic and biotic factors affect communities
Abiotic (non-living) factors like light, temperature, water and mineral levels affect where organisms can live. Biotic (living) factors - competition, predators, disease, availability of food - matter too. A plant might be limited by shade in one place and by grazing animals in another, so both kinds of factor shape a community.
Use quadrats and transects to sample a population
To estimate numbers without counting everything, place quadrats (square frames) randomly and count what falls inside, then scale up to the whole area by comparing areas. A transect line samples how a species changes across a gradient, such as from a path into a field. Random placing keeps the sample fair and the estimate reliable.
Describe food chains and trophic levels
A food chain shows the feeding order: producers (plants) make food by photosynthesis, primary consumers eat them, and predators eat the consumers. Each stage is a trophic level. Only a fraction of the energy passes on at each level - most is lost as heat and waste - which is why food chains rarely run beyond four or five links.
Describe the carbon and water cycles
The carbon cycle recycles carbon: photosynthesis takes CO₂ from the air, respiration, combustion and decay return it. The water cycle moves water by evaporation, condensation into clouds, precipitation as rain, and flow back to the sea. Both cycles keep essential materials circulating so life is not starved of them.
Explain biodiversity and human impacts on the environment
Biodiversity is the variety of species in an ecosystem, and high biodiversity makes a system more stable. Human activities reduce it: pollution, deforestation and using land for farming or building destroy habitats, while burning fossil fuels adds greenhouse gases. Conservation - protecting habitats, recycling, replanting - works to slow this loss.
Ecology key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Habitat
- The place where an organism lives.
- Population
- All the organisms of one species living in a habitat.
- Community
- The populations of all the different species living in a habitat.
- Ecosystem
- The interaction of a community of living organisms with the non-living parts of their environment.
- Abiotic factor
- A non-living factor that affects a community, such as light intensity, temperature or water availability.
- Biotic factor
- A living factor that affects a community, such as food availability, predators or pathogens.
- Interdependence
- The way species in a community depend on each other for food, shelter, pollination and more, so removing one species can affect the whole community.
- Biodiversity
- The variety of all the different species of organisms on Earth, or within an ecosystem. High biodiversity makes ecosystems more stable.
Practice
Try a Ecology question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
A student uses a 0.5 m by 0.5 m quadrat and counts a mean of 5 plantains per quadrat. Estimate the population in a 400 field.
- 8000
- 2000
- 1000
- 10000
Show the answer and the working
Answer: 8000
Work out the quadrat area, then the density per square metre, then multiply by the field area.
- The quadrat is 0.5 m by 0.5 m, so its area is 0.25 .
- Density per = = 20.
- Multiply by the field area: 20 x 400 = 8000 plantains.