Ecosystems and InterdependenceAQA GCSE Biology: Revision notes
Section 1
What Is an Ecosystem?
An ecosystem is the interaction of a community of living organisms (the biotic parts) with the non-living (abiotic) parts of their environment, such as soil, water and climate. Ecosystems can be described at different levels of organisation, from individual organisms, up through populations and communities, to the whole ecosystem. Interdependence and competition between organisms are both important in shaping how a community functions.
Section 2
Competition Between Organisms
Organisms within a community often compete with each other for limited resources:
- Plants compete for light, space, water and mineral ions
- Animals compete for food, mates and territory
Competition can limit population sizes, as not every individual can obtain enough of a resource to survive and reproduce.
Section 3
Interdependence in a Community
Interdependence means that within a community, each species depends on other species for things such as food, shelter, pollination and seed dispersal.
- If one species is removed from a community, this can affect the whole community, because other species that depended on it may also be affected
- A stable community is one where all the species and environmental factors are in balance, so population sizes remain fairly constant over time
Removing bees (pollinators) from an ecosystem could reduce reproduction in many flowering plant species, which in turn affects animals that rely on those plants for food.
Section 4
Adaptations to the Environment
Organisms are adapted to live successfully in their natural environment. Adaptations can be:
- Structural — a physical feature of the body (e.g. thick fur)
- Behavioural — a way an organism acts (e.g. migration)
- Functional — a process inside the body (e.g. producing antifreeze proteins)
Organisms that live in extreme environments, such as very high temperature, pressure or salt concentration, are called extremophiles.
Section 5
Abiotic and Biotic Factors
Both non-living and living factors affect the organisms living in a community:
- Abiotic (non-living) factors: light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels (for plants), oxygen levels (for aquatic animals)
- Biotic (living) factors: availability of food, new predators arriving, new pathogens appearing, one species outcompeting another
If a question gives you a factor and asks whether it's abiotic or biotic, ask whether it is a living thing/interaction (biotic) or a physical/chemical condition (abiotic).
Must Know
- An ecosystem is a community of living organisms (biotic) interacting with the non-living environment (abiotic)
- Plants compete for light, space, water and minerals; animals compete for food, mates and territory
- Interdependence means species rely on each other; removing one species can affect the whole community
- A stable community has population sizes that stay fairly constant because species and environmental factors are balanced
- Adaptations can be structural, behavioural or functional; extremophiles live in extreme conditions
- Abiotic factors (e.g. temperature, light, pH) and biotic factors (e.g. predators, food, pathogens) both affect a community
That's the notes covered.
Carry on to the next subtopic.