AQA GCSE Combined Science Foundation (8464), Foundation tier · Biology › Ecology › Biodiversity and the effect of human interaction on ecosystems
Practise Deforestation. 7 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.
Large areas of tropical forest have been cut down to make room for cattle and rice fields and to grow crops for biofuels. Expect to explain why this happens, and how it reduces biodiversity and increases the carbon dioxide in the atmosphere.
Key facts
Tropical deforestation: land for cattle, rice fields and biofuel crops
Fewer trees → less CO2 removed by photosynthesis
Burning trees → CO2 released by combustion
Rotting wood → microorganisms respire → CO2 released
Habitat loss → lower biodiversity
Notes
Why tropical forests are cut down
Huge areas of tropical forest have been cleared (deforestation) mainly to:
provide land for cattle and for rice fields, producing food for a growing population;
grow crops for biofuels, such as sugar cane or oil palm, which are used to make fuels.
Effect on biodiversity
Tropical forests have very high biodiversity. Clearing them destroys the habitats of many species.
The forest is replaced by grassland for cattle or by large fields of a single crop, which support far fewer species.
Species that live only in that forest may become extinct.
Effect on the atmosphere
diagram
Trees remove carbon dioxide from the air by photosynthesis and store the carbon in their wood. Fewer trees means less carbon dioxide is removed.
The trees are often burned to clear the land. Combustion releases carbon dioxide.
Wood and roots left to rot are broken down by microorganisms, whose respiration releases carbon dioxide.
More carbon dioxide in the atmosphere contributes to global warming.
Three ways deforestation adds carbon dioxide to the air.
Conflicting needs
People in tropical countries need land, food and income, and biofuels are a renewable alternative to fossil fuels.
But clearing forest releases a large amount of carbon dioxide and destroys habitats that cannot quickly be replaced.
How to answer each type of question
Give reasons for deforestation
2 marksGrade 4
Use the reasons in the specification: land for cattle, land for rice fields, crops for biofuels.
Link them to a growing population needing food and fuel if the question asks you to explain.
Example. Give two reasons why large areas of tropical forest have been cut down.
Show the model answerHide the model answer
Any two from: to provide land for cattle (1); to provide land for rice fields (1); to grow crops for biofuels (1)
Explain how deforestation affects biodiversity
2 to 3 marksGrade 5
Say that habitats (food and shelter) are destroyed.
Say that one crop or grazing land replaces the forest, so fewer species can live there.
Conclude that biodiversity falls and species may become extinct.
Example. An area of tropical forest is cleared to grow oil palm. Explain how this affects biodiversity. (3 marks)
Show the model answerHide the model answer
The forest habitat, with food and shelter for many species, is destroyed (1). Only one plant species is grown, so few animal species can find food or shelter there (1). So biodiversity is reduced and some species may become extinct (1).
Don’t lose marks
Writing that deforestation 'means less oxygen for us to breathe'. This rarely scores; focus on carbon dioxide and biodiversity.
Saying the trees 'release carbon dioxide' without the process: combustion when burned, or respiration by microorganisms when they decay.
Forgetting that fewer trees means less photosynthesis, so less carbon dioxide is removed from the air.
More tips
Memory tricks
Reasons, CRB: Cattle, Rice, Biofuels.
Three ways carbon dioxide rises: burning, rotting, and less photosynthesis.
Almost every mark on this subtopic comes from biodiversity or carbon dioxide. Link each point to one of them.
Exam technique
Give three separate ways deforestation increases carbon dioxide: burning, decay and less photosynthesis.
For 6-mark evaluations, include people's needs as well as the environmental costs, and end with a judgement.
Write 'microorganisms respire', not just 'the wood decays'.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define deforestationCutting down large areas of forest so the land can be used for something else.
Grade 4
Give reasons for tropical deforestationTo provide land for cattle and rice fields, and to grow crops for biofuels.
Grade 5
Explain how deforestation reduces biodiversityForest habitats are destroyed and replaced by grazing land or one crop, so many species are lost.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Deforestation means that less carbon dioxide is removed from the atmosphere. Name the process in trees that removes carbon dioxide from the atmosphere.
Photosynthesis
Complete the sentence. Large-scale deforestation in tropical areas has happened to provide land for cattle and ....................... fields, and to grow crops for ....................... .
rice; biofuels
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Large areas of tropical forest have been cut down.
(a) Which two are reasons for large-scale tropical deforestation? Tick (✓) two boxes.[2]
To provide land for cattle and rice fields
To grow crops for biofuels
To increase biodiversity
To reduce the carbon dioxide in the atmosphere
(b) Deforestation means that less carbon dioxide is removed from the atmosphere. Name the process in trees that removes carbon dioxide from the atmosphere.[1]
(c) Give one effect of deforestation on biodiversity. Give a reason for your answer.[2]
Show the answer and mark scheme
(a)Answer: To provide land for cattle and rice fields; To grow crops for biofuels
(b)Answer: Photosynthesis
photosynthesis
(c)
biodiversity is reduced / there are fewer species
because habitats / food / shelter for many species are destroyed / species may become extinct
Question 2Medium6 marks
In some tropical countries, forests are cleared by cutting down the trees and burning them. The land is then used to grow crops.
(a) Explain how clearing forest in this way increases the concentration of carbon dioxide in the atmosphere.[3]