B1.3 Interdependence · KS3 Science

Ecosystems

A habitat is where an organism lives. A population is all the organisms of one species in a habitat. A community is all the populations in a habitat.
An ecosystem is a community of organisms together with the non-living parts of their environment.
Organisms depend on each other for food, shelter, pollination and seed dispersal. This is called interdependence.

Arrows in a food chain show the direction energy is transferred: grass → rabbit → fox.
Producers (plants and algae) make their own food by photosynthesis. Primary consumers (herbivores) eat producers; secondary consumers eat primary consumers.
Predators hunt and eat prey. A food web shows many linked food chains.
A change in one population affects others: if rabbits die out, foxes have less food, and the amount of grass increases.
Each feeding level is a trophic level. Energy is lost at each level (through movement, heat from respiration and waste), so food chains rarely have more than five links.

Abiotic factors are non-living: light, temperature, water, soil pH and minerals, wind.
Biotic factors are living: food supply, predators, disease and competition.
Animals compete for food, water, space (territory) and mates. Plants compete for light, water, space and mineral ions from the soil.

A quadrat is a square frame placed on the ground to count the plants inside it.
Place quadrats randomly, and use lots of them, so the sample represents the whole area and isn't biased.
Estimated population = mean number per quadrat × (total area ÷ area of one quadrat).
A transect is a line along which quadrats are placed, to see how plants change across an area, such as from shade into sunlight.
Pitfall traps, sweep nets and pooters are used to collect small animals.

Habitat: The place where an organism lives.
Population: All the organisms of one species in a habitat.
Community: All the populations of different species in a habitat.
Ecosystem: A community and the non-living parts of its environment.
Interdependence: The way organisms in an ecosystem depend on each other.
Producer: An organism that makes its own food by photosynthesis.
Consumer: An organism that eats other organisms.
Predator: An animal that hunts and eats other animals.
Prey: An animal that is hunted and eaten.
Trophic level: A feeding level in a food chain.
Biotic factor: A living factor that affects an ecosystem, such as disease.
Abiotic factor: A non-living factor that affects an ecosystem, such as temperature.
Quadrat: A square frame used to sample plants.
Competition: When organisms struggle against each other for the same resources.