7.2.1: Levels of organisation
Not started yet — this one needs some love.
Producers: photosynthetic organisms that are the producers of biomass for life on Earth.
Feeding relationships within a community can be represented by food chains.
All food chains begin with a producer which synthesises molecules.
A producer is usually a green plant or alga which makes glucose by photosynthesis.
Primary consumers eat producers.
Secondary consumers eat primary consumers.
Tertiary consumers eat secondary consumers.
Predators are consumers that kill and eat other animals.
Prey are animals eaten by predators.
In a stable community the numbers of predators and prey rise and fall in cycles.
Quadrats are used to sample the abundance of species in a habitat.
Transects are used to investigate how species distribution changes across a habitat.
Mean abundance can be calculated from sample data, then plotted on a graph with suitable axis scales.
Common exam mistakes
In food chain labels, use the trophic role in that chain; an organism can be a different consumer level in a different food chain.
Quadrats should be placed using random coordinates for random sampling, not thrown by hand.
For population size estimates, calculate a mean sample value before scaling up to the whole habitat.
Use transects for changes along a gradient; use random quadrats for an overall population estimate.