GCSE · Biology · AQA · Spec 8461

Levels of organisation in an ecosystem (communities)

Take the bees out of a wood and the blue tits' chicks could go hungry — even though blue tits never eat bees. Build the web and see why.

Biology · Who needs whom?

Build the woodland web

Here are six members of a simple woodland community. Draw an arrow FROM a species TO one that needs it — for food, for shelter, for pollination or to spread its seeds. So each arrow means: that species would be worse off without this one. Aim for five or more links, then compare.

Oak tree
Caterpillars
Blue tits
Jays
Bramble (blackberry bushes)
Bees

Add a link

This factor……made this happen or worse

No links yet.

Biology · Levels of organisation

From one blue tit to the whole wood

How much of the wood each level takes in

1 · Takes in the least4 · Takes in the most

Community
The blue tits, oaks, bees, jays, caterpillars, bramble… every species in the wood
Individual organism
One blue tit
Ecosystem
Every living thing in the wood, plus the soil, water and air around them
Population
All the blue tits in the wood

Watch out: Easy slip: a community is living things only. The moment you add the non-living environment, you are talking about an ecosystem.

Biology · Stable communities

What happens when the foxes go?

A grassland community is stable. Foxes eat rabbits, and rabbits eat the grass. Then all the foxes are removed.

Which is closest to what you think happens next?

Only the rabbits are affected, because they're the only thing the foxes ate.It's good news for the rabbits: with no foxes, they'll just keep increasing.The community is stable, so nothing much will change.Rabbit numbers may rise at first, and the change can spread to the grass and beyond.

How sure are you?

I'm sureI think soI'm guessing

Only the rabbits are affected, because they're the only thing the foxes ate.

This is a common misconception

The rabbits feel it first, but it doesn't stop there. With more rabbits, more grass gets eaten — and anything else that depends on that grass can be affected too. That's the whole point of interdependence: the effect can reach species the foxes never touched.

It's good news for the rabbits: with no foxes, they'll just keep increasing.

This is a common misconception

At first there may well be more rabbits. But more rabbits means more rabbits competing with each other for the same grass. If the grass runs short, rabbits can go hungry and their numbers can fall again. Losing a predator doesn't only help its prey.

The community is stable, so nothing much will change.

This is a common misconception

Stable doesn't mean frozen, and it doesn't mean protected. A stable community is one where all the species and environmental factors are in balance, so population sizes stay fairly constant — they rise and fall a little. Removing the foxes upsets that balance, so things can change a lot.

Rabbit numbers may rise at first, and the change can spread to the grass and beyond.

This matches the evidence

Yes. The balance that kept population sizes fairly constant has been upset. Species depend on each other, so removing one can affect the whole community — not just the species it was directly linked to.

A stable community is balanced, with population sizes staying fairly constant. Because species are interdependent, removing one species can affect the whole community.

Biology · Competition

What are they competing for?

What is being competed for in each case?

Still to sort

Light (0)

Plants compete for this

Where the line is: Light is about shade. A plant can have plenty of room and still be short of light if something grows over it.

Space (0)

Plants compete for this

Where the line is: Space is room to grow. For animals, an area that is defended against rivals is called territory.

Water and mineral ions from the soil (0)

Plants compete for these, through their roots

Food (0)

Animals compete for this

Mates (0)

Animals compete for these

Territory (0)

Animals compete for this

Where the line is: Two animals feeding in the same place are competing for food. Chasing rivals away from an area is about territory.

8 of 8 still to sort.

Species depend on each other — but they also compete. Read each clue and decide what is in short supply.

Maths · Reading data

Crowded pots, smaller plants

Illustrative results: radish plants grown with 1, 2, 4, 8 or 16 plants in each pot. Tap a bar to read it.

Every pot had the same soil, the same water and the same light. Only the number of plants sharing it changed. Tap a bar to see its value.

Mean

Median

3.4

Mode

4.2

Range

3.1

Exam line: Describe, then explain. Describe: as the number of plants per pot rose from 1 to 16, the mean mass of each plant fell from 4.2 g to 1.1 g — though 1 and 2 plants per pot gave the same mass, so the pot seems to have had enough for two. Explain: once more plants were sharing the same light, space, water and mineral ions, each plant got less — they were competing.

Watch out: Use numbers from the chart, with units. 'It fell from 4.2 g to 1.1 g' says far more than 'it went down'.

Biology · Suggest how it's adapted

Living in the oak's shadow

A small plant grows on the floor of an oak wood. From early summer, the oak's leaves above block most of the light. The plant grows its leaves and flowers in early spring, before the oak's leaves open. Its leaves are broad and thin. It stores food in a bulb underground.

Suggest how this plant is adapted to the conditions on the woodland floor. [3 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

It grows and flowers in early spring, so it gets light before the oak's leaves shade the ground (1 mark)
Its broad leaves have a large surface to absorb as much light as possible (1 mark)
The food stored in its bulb lets it grow quickly as soon as spring starts, while light still reaches the ground (1 mark)

Model answer

The plant grows its leaves and flowers early in spring, so it gets light before the oak's leaves open and shade the ground. Its leaves are broad, giving a large surface to absorb as much light as possible. The food stored in its bulb lets it grow quickly as soon as spring begins, while light is still getting through to the woodland floor.

The trick with 'suggest' questions: link every feature to a condition you were given. Feature → condition → how it helps. Three features, three links.

UK note

In AQA GCSE Biology, questions on this topic can describe an organism you have never met and ask you to suggest how it is adapted to where it lives, or what organisms in a habitat are competing for. The credit comes from linking each feature or clue to the information you are given. Ecology is assessed on Paper 2.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Every species needs others — for food, for shelter, to pollinate its flowers or to spread its seeds. Build the web yourself, then see how far one missing species can reach.

What you need to know

The levels of organisation, from least to most inclusive: individual organism → population → community → ecosystem.
An ecosystem is the interaction of a community of living (biotic) organisms with the non-living (abiotic) parts of their environment.
Within a community, each species depends on other species for food, shelter, pollination, seed dispersal and more. If one species is removed, it can affect the whole community. This is interdependence.
Plants often compete with each other for light and space, and for water and mineral ions from the soil. Animals often compete for food, mates and territory.
A stable community is one where all the species and environmental factors are in balance, so that population sizes remain fairly constant.

The big picture

Living things are organised in levels: individual organism, population, community and ecosystem. An ecosystem is a community of living (biotic) organisms interacting with the non-living (abiotic) parts of their environment. Within a community, each species depends on others for things like food, shelter, pollination and seed dispersal, so removing one species can affect the whole community — that is interdependence. Organisms also compete: plants for light, space, water and mineral ions, and animals for food, mates and territory. A stable community is one in balance, where population sizes stay fairly constant.

Key points

1A population is all the individuals of one species in an area. A community is all the populations of different species living there together.

2To survive and reproduce, organisms need a supply of materials from their surroundings and from the other living organisms there.

3Follow the links: removing a species can reach species that were never directly linked to it.

4Given information about a habitat, look for what several organisms need and is in short supply — that is what they are competing for.

5Given information about where an organism lives, link each of its features to a condition to suggest how it is adapted.

6With a chart about interacting organisms, describe the pattern with numbers first, then link it to competition or interdependence.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

In a pond, snails eat pondweed, and fish eat the snails. The fish do not eat pondweed. Explain how removing all the pondweed could affect the fish.

⚠ Watch out

Saying that removing a species only affects the species that eat it or that it eats. Because species are interdependent, the effect can spread through the community to species with no direct link to the one removed.

🧠

Memory hook

One, all of one kind, all the kinds, all the kinds plus the place: individual → population → community → ecosystem. And in a community, tug one thread and the whole web can shake.

✓

Check yourself

Without looking back: put the four levels of organisation in order and say what an ecosystem has that a community doesn't. Then name three things plants compete for and three things animals compete for.

Flashcards

(12)

What is an ecosystem?

The interaction of a community of living (biotic) organisms with the non-living (abiotic) parts of their environment.

Put these in order from least to most inclusive: community, individual, ecosystem, population.

Individual organism → population → community → ecosystem.

What is a population?

All the individuals of one species living in the same area.

What is a community?

All the populations of different species living and interacting in the same area.

What does 'biotic' mean, and what does 'abiotic' mean?

Biotic means living. Abiotic means non-living.

Name four things a species can depend on other species for.

Food, shelter, pollination and seed dispersal.

What is interdependence?

Species in a community depend on each other, so if one species is removed it can affect the whole community.

What do plants often compete with each other for?

Light, space, and water and mineral ions from the soil.

What do animals often compete with each other for?

Food, mates and territory.

What is a stable community?

One where all the species and environmental factors are in balance, so population sizes remain fairly constant.

In a stable community, do population sizes stay exactly the same?

No — they stay fairly constant. They rise and fall a little, but stay in balance.

What do organisms need from their surroundings and from other living things?

A supply of materials, so that they can survive and reproduce.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

Build the woodland web

From one blue tit to the whole wood

What happens when the foxes go?

What are they competing for?

Crowded pots, smaller plants

Living in the oak's shadow

More AQA GCSE Biology topics