AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Ecology › Biodiversity and the effect of human interaction on ecosystems
Practise Biodiversity. 5 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Biodiversity is the variety of all the different species on Earth or in an ecosystem. You need to explain why high biodiversity makes ecosystems stable and why it matters to humans. Expect definitions and 2 to 3 mark 'explain' questions, often at the start of a longer question on human impacts.
Key facts
Biodiversity = the variety of all the different species on Earth or in an ecosystem
High biodiversity → more stable ecosystem
Why: species depend less on any one species for food, shelter and maintaining the physical environment
The future of humans relies on maintaining biodiversity
Many human activities reduce biodiversity
Notes
What biodiversity is
Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.
An ecosystem with many different species, such as a tropical rainforest or a coral reef, has high biodiversity. A field of a single crop has low biodiversity.
Why it makes ecosystems stable
diagram
High biodiversity keeps an ecosystem stable, because each species is less dependent on any one other species for food, shelter and keeping the physical environment suitable.
In a food web with many species, if one food source declines, animals can eat something else, so their populations are less affected.
Example: a bird that eats ten kinds of insect is less affected if one insect species dies out than a bird that eats only one kind.
The more species in a food web, the less any one species depends on another.
Many plant species together help keep the physical environment suitable, e.g. roots hold the soil together and leaves shade the ground, so losing one species matters less.
In an ecosystem with low biodiversity, the loss of one species can cause large changes to many others.
Humans and biodiversity
Our own future as a species depends on keeping a good level of biodiversity.
We depend on other species for food, materials such as wood, and many medicines, and on insects to pollinate many crops.
Many human activities are reducing biodiversity, e.g. pollution, building, quarrying, growing single crops, deforestation and global warming.
Serious efforts to slow this loss have only started quite recently.
How to answer each type of question
Define biodiversity
1 markGrade 3
Use the words 'variety' and 'different species'.
Add 'on Earth or in an ecosystem'.
Example. What is meant by biodiversity?
Show the model answerHide the model answer
The variety of all the different species (of organisms) on Earth or in an ecosystem (1).
Don’t lose marks
Defining biodiversity as 'the number of organisms'. It is the variety of different species.
Saying high biodiversity means 'more food'. The key idea is less dependence on any one species.
Forgetting that humans depend on biodiversity too.
More tips
Memory tricks
Biodiversity = 'bio' (life) + 'diversity' (variety): the variety of life.
More species means more back-ups: if one food source disappears, there is another.
Exam technique
Use the phrase 'less dependent on one species' in stability answers.
When comparing biodiversity from data, quote the numbers of species.
Biodiversity questions often lead into longer questions on human impacts. Link back to biodiversity in your conclusion.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define biodiversityThe variety of all the different species of organisms on Earth, or within an ecosystem.
Grade 4
Name human activities that reduce biodiversityFor example pollution, building, farming, deforestation and destroying peat bogs.
Grade 5
Explain why biodiversity matters to humansThe future of humans relies on it, e.g. for food, materials, medicines and stable ecosystems.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Complete the sentence. Biodiversity is the variety of all the different ....................... of organisms on Earth, or within an ....................... .
species; ecosystem
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Many human activities are reducing biodiversity.
(a) What is meant by biodiversity? Tick (✓) one box.[1]
The number of individuals of one species in a habitat
The variety of all the different species of organisms on Earth, or within an ecosystem
The mass of living material at each trophic level
The number of different habitats in an area
(b) A high biodiversity helps to keep an ecosystem stable. Give two reasons why.[2]
(c) Give one human activity that reduces biodiversity.[1]
Show the answer and mark scheme
(a)Answer: The variety of all the different species of organisms on Earth, or within an ecosystem
(b)
species depend less on one other species for food
species depend less on one other species for shelter
species depend less on one other species for the maintenance of the physical environment
if one species is lost, other species can replace it / other food sources are available
(c)
deforestation
building
pollution (of air, water or land)
farming large areas with only one crop
destroying peat bogs
quarrying
overfishing / hunting
Question 2Medium7 marks
Students surveyed the invertebrate animals in two ponds, A and B, using the same method. {table} shows the results.
[object Object]
(a) How many species were found in pond B?[1]
(b) A student said: ‘Pond B has a higher biodiversity than pond A because more animals were found in it.’ Explain why the student is wrong.[2]
(c) Pond B receives run-off water from a farm. Suggest why pond B has a lower biodiversity than pond A.[2]
(d) Explain why an ecosystem with a high biodiversity is more stable.[2]
Show the answer and mark scheme
(a)Answer: 4
4
(b)
biodiversity is the variety / number of different species, not the number of individuals
pond A has more species (7) than pond B (4)
(c)
pollution (e.g. from fertiliser / sewage / pesticides) from the farm
kills some species, so only species that can tolerate the pollution survive
(d)
species are less dependent on one other species for food / shelter
if one species declines, others can use other food sources / replace it, so population sizes stay fairly constant