How materials are cycled - AQA GCSE Biology Exam Questions

Practise 36 exam-style questions on How materials are cycled for AQA GCSE Biology. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

36 questions
2–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

3 marks

Explain why carbon stored as fossil fuels is not part of the fast carbon cycle.

Model answer

Fossil fuels formed from dead organisms buried and decomposed very slowly; carbon is locked away for millions of years and not rapidly exchanged with atmosphere/biota, so it is part of the slow geological carbon cycle.

Explanation

Fossil fuels store carbon for geological timescales, unlike plant and animal biomass and soil carbon which cycle more rapidly through photosynthesis and respiration.

Mark scheme

1 mark
formed over very long timescales from buried organic material
1 mark
carbon is locked away / not available to living organisms for long periods
1 mark
not rapidly exchanged with atmosphere; only released when combusted (human activity)

Question 2

4 marks

A graph shows carbon dioxide concentration in a rainforest falling after sunrise, reaching minimum at midday, then rising in the evening. Explain why CO2 falls after sunrise and rises in the evening.

Model answer

After sunrise photosynthesis starts and removes CO2 faster than respiration ? CO2 concentration falls. By evening photosynthesis decreases (light limiting) but respiration continues, so CO2 released exceeds uptake ? concentration rises.

Explanation

Daylight enables photosynthesis which uses CO2 faster than respiration releases it, lowering CO2. In darkness photosynthesis stops while respiration continues, raising CO2 again.

Mark scheme

1 mark
after sunrise photosynthesis starts
1 mark
photosynthesis removes CO2 from the air
1 mark
in evening photosynthesis decreases / stops (light limiting)
1 mark
respiration continues releasing CO2 so level rises

Question 3

4 marks

Interpretation: A graph shows rising atmospheric CO2 and a corresponding increase in average global temperature over 50 years. Name two lines of evidence that support a causal link between atmospheric CO2 and global warming.

Model answer

Correlation over time plus physical mechanism (greenhouse effect of CO2); lab and radiative forcing measurements show CO2 traps heat; isotope analysis indicates fossil fuel CO2 increase; climate models show CO2 increases cause warming.

Explanation

Multiple lines—observational, experimental, isotopic and modelling—link rising CO2 to warming through the greenhouse effect and sources from fossil fuel emissions.

Mark scheme

1 mark
mechanism: CO2 is a greenhouse gas that traps heat (radiative forcing)
1 mark
measured increase in atmospheric CO2 from fossil fuel combustion (isotope evidence)
Accept mention of isotope C13/C12
1 mark
experimental/laboratory or satellite measurements show CO2 absorbs infrared radiation
1 mark
climate models reproduce observed warming when CO2 increases are included

Question 4

5 marks

Explain why conserving microbial biodiversity in soils is important for nutrient cycling and crop productivity.

Model answer

Microbial biodiversity ensures a range of decomposition pathways and nutrient transformations (e.g. mineralisation, nitrification) so nutrients are available to plants; diverse microbes increase resilience to environmental change and disease, maintain soil structure and fertility, and support plant growth and yield.

Explanation

A rich soil microbial community supports all steps of nutrient cycling, making essential minerals available to crops and maintaining soil health which underpins long-term agricultural productivity.

Mark scheme

1 mark
microbes decompose organic matter and release mineral nutrients
1 mark
different microbes carry out different processes (nitrification, fixation, mineralisation)
1 mark
diversity increases resilience and stability of nutrient cycling under change
1 mark
maintains soil structure and fertility
1 mark
all contribute to sustained crop productivity and yields

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