Practise 36 exam-style questions on Decomposition (biology only) 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
Instant marking
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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
Describe how low moisture content in soil affects decomposition rate and suggest one gardener’s action to improve decomposition in dry soil.
Model answer
Low moisture limits microbial activity and enzyme function so decay slows. Gardener can add water or mulch to retain moisture or irrigate the soil.
Explanation
Decomposers need water for metabolism; maintaining moist conditions (watering, mulching) supports faster decomposition.
Mark scheme
1 mark
low moisture limits microbial activity / enzymes so decay slows
1 mark
gardener action: water / irrigate / add mulch
1 mark
retain moisture to increase microbial activity
Can be implied by action
Question 2
3 marks
Explain why composting at around 60°C for a short period is useful in managed composting.
Model answer
Temperatures around 60°C speed up microbial activity and enzyme rates causing rapid decomposition and also kill many pathogens and weed seeds; maintain for short period so heat-loving microbes work without killing all decomposers.
Explanation
Thermophilic phase at ~60°C accelerates decay and sanitises compost, but temperature must be controlled to maintain a healthy microbial community.
Mark scheme
1 mark
60°C increases microbial activity and enzyme rates (faster decomposition)
1 mark
also kills pathogens and weed seeds
1 mark
short period prevents killing all beneficial microbes
Question 3
4 marks
A sealed biogas digester produces methane by anaerobic decay. Describe how farmers can use biogas generators to produce fuel and name two advantages.
Model answer
Farmers feed organic waste into a sealed anaerobic digester where anaerobic microbes produce methane which is collected as biogas for cooking or heating. Advantages: renewable energy source; reduces waste and odour; produces nutrient-rich digestate as fertiliser; reduces greenhouse gas emissions if methane captured.
Explanation
Anaerobic digestion converts waste to methane; capturing it provides on-farm fuel and reduces waste and greenhouse emissions; the leftover digestate can be used as fertiliser.
Mark scheme
1 mark
organic waste in sealed tank, anaerobic microbes produce methane (biogas)
1 mark
collect methane for fuel (cooking / heating / electricity)
1 mark
advantage: renewable energy / reduces fossil fuel use
A gardener wants to speed decay of woody prunings. Describe two mechanical and two biological methods to accelerate decomposition.
Model answer
Mechanical: chip or shred wood to increase surface area; composting in smaller pieces and turning pile to aerate. Biological: add nitrogen-rich materials or manure to balance C:N; inoculate with compost or fungal cultures to introduce wood-degrading organisms.
Explanation
Shredding and turning increase surface area and oxygen; adding nitrogen or inoculum introduces necessary nutrients and organisms for breaking down lignocellulose.
Mark scheme
1 mark
mechanical: chip or shred wood to increase surface area
1 mark
mechanical: turn pile / mix / aerate
1 mark
biological: add nitrogen-rich green material / manure
1 mark
biological: add compost inoculum or wood-degrading fungi
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