AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Ecology › Adaptations, interdependence and competition
Practise Communities. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The key words ecologists use (population, community, habitat, ecosystem), what plants and animals compete for, and how the species in a community depend on each other. Expect 1-mark definitions, 'suggest what they compete for' questions and 2 to 4 mark questions on how a change to one species in a food web affects the others.
Key facts
Population = all the organisms of one species in a habitat
Community = all the populations of different species in a habitat
Habitat = the place where an organism lives
Ecosystem = a community interacting with the abiotic (non-living) parts of its environment
Plants compete for light, space, water and mineral ions
Animals compete for food, mates and territory
Interdependence = species depend on each other for food, shelter, pollination and seed dispersal
Stable community = species and environmental factors in balance, so population sizes stay fairly constant
Notes
Key words
Individual: a single organism.
Population: all the organisms of one species living in a habitat.
Community: all the populations of different species living in a habitat.
Habitat: the place where an organism lives.
Ecosystem: the interaction of a community of living organisms (the biotic part) with the non-living (abiotic) parts of their environment.
Levels of organisation, from smallest to largest: individual → population → community → ecosystem.
Competition
Every organism needs resources from its surroundings, and from other organisms, in order to survive and reproduce. When a resource is in short supply, organisms compete for it.
Plants compete for light and space, and for water and mineral ions from the soil.
Animals compete for food, mates and territory.
Competition can be between members of the same species or between different species.
The organisms that are best at getting a scarce resource are the most likely to survive and reproduce.
Interdependence and stable communities
In a community, species rely on one another for food, shelter, pollination and seed dispersal. This is interdependence.
Because species are linked, removing or adding one species can affect the whole community, not just the organisms it eats or is eaten by.
Example: if the bees that pollinate a plant decline, the plant makes fewer seeds, so the animals that eat those seeds have less food.
A stable community is one where all the species and environmental factors are in balance, so population sizes remain fairly constant.
Reading food webs
diagram
Arrows point from the organism that is eaten to the organism that eats it.
A food web: each arrow points from the food to the animal that eats it. Plants (green) are at the bottom.
If an animal's food decreases, its population may fall, but only a little if it has other food sources.
If a predator is removed, its prey may increase at first, then fall again if they run out of food.
How to answer each type of question
Recall: define an ecological term
1 to 2 marksGrade 3
Learn the definitions exactly: 'one species' for a population, 'different species' for a community.
For an ecosystem, mention the living community, the non-living environment and that they interact.
Example. (a) What is meant by a population? (1 mark) (b) What is meant by an ecosystem? (2 marks)
Show the model answerHide the model answer
(a) All the organisms of one species living in a habitat (1) (b) The interaction of a community of living organisms (1) with the non-living parts of their environment (1)
Suggest what organisms are competing for
1 to 2 marksGrade 4
Plants: choose from light, space, water and mineral ions.
Animals: choose from food, mates and territory.
Use the context: plants packed closely together are likely to compete for light and space.
Never write 'food' or 'nutrients' for plants.
Example. (a) A farmer plants sunflowers very close together. Suggest two resources the sunflowers compete for. (2 marks) (b) In autumn, male red deer fight each other. Suggest what they are competing for. (1 mark)
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(a) Any two from: light (1); space (1); water (1); mineral ions (1) (b) Mates (1)
Explain interdependence using an example
2 marksGrade 5
Say what each species depends on the other for (food, shelter, pollination or seed dispersal).
Use the organisms named in the question for both directions of the relationship.
Example. Squirrels eat hazelnuts. They also bury some hazelnuts to eat later, and some of the buried nuts grow into new hazel trees. Explain why squirrels and hazel trees are interdependent.
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Squirrels depend on hazel trees for food (1). Hazel trees depend on squirrels to disperse their seeds, because buried nuts that are not eaten can grow into new trees (1).
Don’t lose marks
Saying plants compete for 'food' or 'nutrients'. Plants make their own food; write light, space, water or mineral ions.
Mixing up a population (one species) and a community (all the species).
Defining an ecosystem as 'where organisms live'. That is a habitat; an ecosystem includes the non-living environment and the interactions.
Giving an effect without a reason ('the ladybirds decrease'), or ignoring that an animal has other food sources.
Reading food web arrows the wrong way round.
More tips
Memory tricks
Size ladder: individual → population → community → ecosystem. One organism, then one species, then many species, then many species plus the non-living world.
Plants compete for 'Lovely Sunflowers Want Minerals': Light, Space, Water, Mineral ions. Animals compete for Food, Mates and Territory.
Food web arrows mean 'is eaten by': they always point towards the eater.
Exam technique
In 'suggest' questions, use the organisms and resources in the question. Answers linked to the context score best.
For knock-on effects, write a chain linked by 'so': fewer X, so less food for Y, so Y decreases.
When a question says 'give two', give exactly two. A wrong extra answer can cancel a correct one.
Use the terms interdependence and stable community exactly as defined.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define population, community, habitat and ecosystemA population is one species in a habitat, a community is all the populations there, and an ecosystem is the community interacting with the non-living environment.
Grade 4
List what plants compete forLight and space, and water and mineral ions from the soil.
Grade 4
List what animals compete forFood, mates and territory.
Grade 5
Explain what interdependence meansEach species depends on others for food, shelter, pollination or seed dispersal, so removing one species can affect the whole community.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Write these levels of organisation in order, from the smallest to the largest. community · ecosystem · individual organism · population
individual organism → population → community → ecosystem
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
Ecologists use special terms to describe organisms and their surroundings.
(a) Which term describes all the populations of different species living in a habitat? Tick (✓) one box.[1]
Community
Ecosystem
Population
Species
(b) What is an ecosystem? Tick (✓) one box.[1]
All the organisms of one species living in a habitat
The interaction of a community of living organisms with the non-living parts of their environment
The place where an organism lives
The variety of all the different species on Earth
(c) Plants in a community compete with each other. Give two things that plants compete for.[2]
(d) Animals in a community also compete with each other. Give two things that animals compete for.[2]
Show the answer and mark scheme
(a)Answer: Community
(b)Answer: The interaction of a community of living organisms with the non-living parts of their environment
(c)
light
space
water
mineral ions
(d)
food
mates
territory
water / shelter
Question 2Medium8 marks
Bluebells are plants that grow on the floor of deciduous woodlands. Bluebells grow new leaves and flower in early spring, before the leaves on the trees have fully opened.
(a) Suggest how growing leaves and flowering in early spring helps bluebells to compete with the trees.[2]
(b) Trees and bluebells also compete for resources from the soil. Name two of these resources.[2]
(c) Bees feed on nectar from bluebell flowers and carry pollen between the flowers. Explain why bluebells and bees are interdependent.[2]
(d) Deer eat bluebell leaves. Suggest how an increase in the number of deer in the woodland could affect the bees.[2]
Show the answer and mark scheme
(a)
more light reaches the woodland floor before the tree leaves open
(so) bluebells can absorb more light / photosynthesise more
(b)
water
mineral ions
(c)
bees depend on bluebells for food / nectar
bluebells depend on bees for pollination / to reproduce
(d)
fewer bluebells / bluebell flowers (because leaves are eaten)
(so) less nectar / food for bees, so the number of bees may fall