AQA GCSE Combined Science (8464), Higher tier · Biology › Ecology › Biodiversity and the effect of human interaction on ecosystems
Practise Biodiversity. 11 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.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Define biodiversityThe variety of all the different species of organisms on Earth, or within an ecosystem.
4
Name human activities that reduce biodiversityFor example pollution, building, farming, deforestation and destroying peat bogs.
5
Explain why biodiversity matters to humansThe future of humans relies on it, e.g. for food, materials, medicines and stable ecosystems.
6
Explain why high biodiversity makes ecosystems stableSpecies depend less on any one other species for food, shelter and maintaining the physical environment.
7
Compare the stability of two ecosystemsUse the numbers of species to explain which is more likely to be badly affected by a change.
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
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.
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.
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
The future of the human species on Earth relies on us maintaining 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.
Only recently have measures been taken to try to stop this reduction.
Cheatsheet
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
How to answer each type of question
Define biodiversity
1 mark3
Use the words 'variety' and 'different species'.
Add 'on Earth or in an ecosystem'.
Example. What is meant by biodiversity?
Show the model answer
The variety of all the different species (of organisms) on Earth or in an ecosystem (1).
Explain why high biodiversity makes an ecosystem stable
2 marks6
Say that species depend less on any single species (for food, shelter or maintaining the environment).
Say that if one species is lost, others can be eaten or used instead, so populations change less.
Example. Explain why an ecosystem with high biodiversity is more stable than one with low biodiversity.
Show the model answer
With high biodiversity, species depend less on any one other species for food or shelter (1). If one species declines, animals can eat other species instead, so the populations of other species do not change as much (1).
Compare two ecosystems using data
3 marks7
Compare the numbers of species, quoting the data.
Say which ecosystem has lower biodiversity.
Explain why it would be affected more, using the idea of dependence.
Example. A natural woodland contains 48 species of plant and 130 species of insect. A conifer plantation contains 6 species of plant and 25 species of insect. A disease kills one species of tree in each. Suggest which ecosystem is likely to be affected more. Explain your answer.
Show the model answer
The conifer plantation (1). It has lower biodiversity, e.g. 6 plant species compared with 48 (1). So the insects and other animals have fewer other sources of food and shelter, and the loss of one tree species affects more of them (1).
Shortcuts and 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.
Where marks are lost
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.
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.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Estimate how many of the untested species could contain a chemical that could be developed into a useful medicine.
22.4 (about 22)
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
Question 3Hard9 marks
The future of the human species on Earth relies on us maintaining a good level of biodiversity. Scientists studying a tropical forest estimate that 1 in every 125 plant species contains a chemical that could be developed into a useful medicine. The forest contains about 4000 plant species. 2800 of these species have not yet been tested.
(a) Estimate how many of the untested species could contain a chemical that could be developed into a useful medicine.[2]
(b) Clearing the forest for farming is predicted to destroy 30% of the untested species before they can be tested. A newspaper headline said: 'Forest clearance will destroy 7 new medicines.' Use a calculation and the information given to evaluate this headline.[3]
(c) Give two other reasons why humans depend on maintaining biodiversity.[2]
(d) Only recently have measures been taken to try to stop the reduction in biodiversity. Suggest two reasons why.[2]
Show the answer and mark scheme
(a)Answer: 22.4 (about 22)
2800 ÷ 125
22.4 / about 22
(b)Answer: 22.4 × 0.30 ≈ 7, but the figures are only estimates, so the headline is too certain
22.4 × 0.30 = 6.7, so about 7 is consistent with the scientists' estimates
but '1 in 125' and '30%' are only estimates / predictions, so the real number could be higher or lower
'will destroy' is too certain: the same chemicals may be found in other species or places / could be made artificially
not every useful chemical becomes a medicine: it must pass testing / trials first
(c)
food, e.g. crops, fish, wild animals
materials, e.g. timber, fibres, fuel
pollination of crops by insects
wild relatives of crops carry alleles that are useful for breeding, e.g. for disease resistance
stable ecosystems provide clean water, oxygen, fertile soil or flood protection
(d)
scientists did not have enough data about how quickly species were being lost
the importance of biodiversity to humans was not understood
there is conflict with economic pressures, e.g. land needed for farming / building
protecting biodiversity needs international agreement / cooperation / funding