AQA GCSE Biology (8461) — Ecology
Understanding how energy moves through an ecosystem explains how sunlight ultimately powers almost every living animal on Earth.
Biomass is transferred through an ecosystem step-by-step via feeding relationships, which are represented by food chains.
If you track the number of wild hares and lynxes in a forest over decades, you will not see flat lines—you will see a continuous, repeating rollercoaster of population booms and busts.
Graphing this population data reveals a distinct, cyclical mechanism:
When interpreting these graphs, you will notice a characteristic lag time.
Never write that arrows in a food chain show 'what eats what'. You must explicitly state that the arrows represent the direction of biomass and energy transfer.
In 6-mark questions interpreting predator-prey graphs, examiners actively look for the phrases 'out-of-phase' and 'lag time' to describe the relationship between the population peaks.
Predator-prey cycles only predictably occur in stable communities. If asked why a cycle might break, remember that predation is a biotic factor, and sudden abiotic factors (like a harsh winter killing the prey's food source) or new biotic factors (like a new disease) can disrupt the balance.
Producers
Photosynthetic organisms (like green plants or algae) that synthesise molecules and build biomass using energy from sunlight.
Trophic level
The position or feeding level an organism occupies in a food chain.
Biomass
The total mass of living material in an organism or at a specific trophic level.
Primary consumer
A herbivore that eats producers.
Secondary consumer
A carnivore that eats primary consumers.
Predator
A consumer that kills and eats other animals.
Prey
An animal that is killed and eaten by a predator.
Tertiary consumer
A carnivore that eats secondary consumers.
Apex predator
A carnivore at the very top of a food chain that has no natural predators.
Stable community
A community where all species and environmental factors are in balance so that population sizes remain fairly constant over time.
Lag time
The characteristic time delay in the response of a predator population to a change in prey numbers, caused by the time needed for reproduction and growth.
Put your knowledge into practice — try past paper questions for Biology
Producers
Photosynthetic organisms (like green plants or algae) that synthesise molecules and build biomass using energy from sunlight.
Trophic level
The position or feeding level an organism occupies in a food chain.
Biomass
The total mass of living material in an organism or at a specific trophic level.
Primary consumer
A herbivore that eats producers.
Secondary consumer
A carnivore that eats primary consumers.
Predator
A consumer that kills and eats other animals.
Prey
An animal that is killed and eaten by a predator.
Tertiary consumer
A carnivore that eats secondary consumers.
Apex predator
A carnivore at the very top of a food chain that has no natural predators.
Stable community
A community where all species and environmental factors are in balance so that population sizes remain fairly constant over time.
Lag time
The characteristic time delay in the response of a predator population to a change in prey numbers, caused by the time needed for reproduction and growth.
