GCSE · Biology · AQA · Spec 8461

Biodiversity

One ecosystem holds a great variety of species, another only a few. Which stays steadier — and what is it about variety that makes the difference?

Build the web

What acts on biodiversity — and what does it act on?

Six ideas. Draw an arrow from each idea to the idea it acts on. An arrow can mean 'reduces', 'tries to protect', 'leads to' or 'supports'. Direction matters, so ask which idea comes first. Then compare with the lesson's web.

Biodiversity
Less dependence of one species on another
Stability of the ecosystem
The future of the human species on Earth
Human activities
Measures to stop biodiversity being reduced

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Pin down the word

What does biodiversity actually mean?

Which is closest to what you think biodiversity means right now?

How many living things there are — the more organisms, the greater the biodiversity.It only applies to the whole planet: the variety of species on Earth.It only applies to one place: the range of species in a single ecosystem.The variety of all the different species of organisms, on Earth or within an ecosystem.

How sure are you?

I'm sureI think soI'm guessing

How many living things there are — the more organisms, the greater the biodiversity.

This is a common misconception

Biodiversity is about variety, not a head count. It is the variety of all the different species, so what matters is how many different kinds of organism there are. Huge numbers of organisms from only a few species are still little variety.

It only applies to the whole planet: the variety of species on Earth.

This is a common misconception

That is half of it. Biodiversity is the variety of all the different species on Earth, or within an ecosystem. It describes a single ecosystem too, and that is the scale at which it keeps an ecosystem stable.

It only applies to one place: the range of species in a single ecosystem.

This is a common misconception

The right idea at too small a scale. Biodiversity can describe one ecosystem, but it also describes the variety of all the different species on Earth as a whole.

The variety of all the different species of organisms, on Earth or within an ecosystem.

This matches the evidence

Yes. Variety of different species (kinds of organism, not a head count), at either scale: the whole Earth, or one ecosystem.

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem. Count kinds, not individuals, and remember both scales.

Predict, then check

Commit to an answer before you reveal it.

Ecosystem P has a great variety of different species. Ecosystem Q has only a few different species. Which is more likely to stay stable, and why?

Now write it

Explain why losing biodiversity matters

Many human activities are reducing biodiversity. Explain why this is a concern. [4 marks]

Your answer

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The mark scheme

A great biodiversity ensures the stability of ecosystems. (1 mark)
It does this by reducing the dependence of one species on another. (1 mark)
Names what species depend on each other for: food, shelter or the maintenance of the physical environment. (1 mark)
The future of the human species on Earth relies on us maintaining a good level of biodiversity. (1 mark)

Model answer

A great biodiversity keeps ecosystems stable. It works by reducing how much one species depends on another for food, shelter and keeping the physical environment maintained, so losing variety takes that protection away. Our own future matters too: the human species relies on us maintaining a good level of biodiversity.

Four separate ideas, each worth its own tick: stability, reduced dependence, what species depend on each other for, and the human future. The question already told you biodiversity is being reduced, so repeating that earns nothing.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The variety of species — and why an ecosystem with more of it stands steadier.

What you need to know

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.
A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment.
The future of the human species on Earth relies on us maintaining a good level of biodiversity.
Many human activities are reducing biodiversity, and only recently have measures been taken to try to stop this reduction.

The big picture

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem. A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment. The future of the human species on Earth relies on us maintaining a good level of biodiversity. Many human activities are reducing biodiversity, and only recently have measures been taken to try to stop this reduction.

Key points

1Biodiversity means variety of different species, not the number of organisms — measured for the whole Earth or for one ecosystem.

2More variety means less dependence of one species on another, and that keeps an ecosystem stable.

3Species depend on one another for food, for shelter and for the maintenance of the physical environment.

4Human activities are pushing biodiversity down; measures to stop this are only recent.

5Our future as a species relies on maintaining a good level of biodiversity.

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Worked example

Problem

A student writes: 'An ecosystem that is stable will have a great biodiversity.' Rewrite the sentence so the relationship runs the right way round, and add how it works.

⚠ Watch out

Treating biodiversity as the number of living things. It is the variety of different species — a place packed with organisms from only a few species has little biodiversity.

🧠

Memory hook

Many kinds, less leaning: when there are lots of different species, no species leans too hard on any other — so the ecosystem stays steady.

✓

Check yourself

Cover the page and finish this in your own words: 'A great biodiversity keeps an ecosystem stable because…' Then name the two things that act on biodiversity.

Flashcards

(7)

What is biodiversity?

The variety of all the different species of organisms on Earth, or within an ecosystem.

Biodiversity: a count of organisms, or a variety of species?

A variety of different species. Lots of organisms from only a few species is still low biodiversity.

Why does an ecosystem with many different species stay steadier than one with few?

Each species relies less heavily on any single other species.

For which three things can one species depend on another?

Food, shelter, and the maintenance of the physical environment.

What does the future of the human species on Earth rely on?

Us maintaining a good level of biodiversity.

What effect are many human activities having on biodiversity?

They are reducing it.

How long have measures been taken to stop the reduction in biodiversity?

Only recently.

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.

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What acts on biodiversity — and what does it act on?

What does biodiversity actually mean?

Explain why losing biodiversity matters

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