A student leaves a piece of bread in a warm, damp environment. After two weeks, the bread is covered in mould and has significantly decreased in mass. Explain why the conditions in the student's environment led to the bread decaying rapidly, and describe what happens to the materials in the bread during decomposition.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Decomposers such as bacteria and fungi break down dead organic material. The rate of decomposition is affected by temperature, moisture and oxygen availability. During decomposition, complex organic molecules are broken down and nutrients are released back into the environment.
Model answer (5 marks)
Warm temperatures increase the activity of enzymes produced by decomposers, so the mould grows faster.
Moist, damp conditions are required for fungi and bacteria to survive and to secrete their enzymes.
The mould secretes enzymes onto the bread that hydrolyse the complex carbohydrates, proteins and fats into simpler molecules.
These molecules are further broken down into very small compounds such as CO₂, H₂O and mineral ions.
The small molecules and ions are released into the surrounding environment, where they are taken up by other organisms, mainly plants, completing the nutrient cycle.
Moist, damp conditions are required for fungi and bacteria to survive and to secrete their enzymes.
The mould secretes enzymes onto the bread that hydrolyse the complex carbohydrates, proteins and fats into simpler molecules.
These molecules are further broken down into very small compounds such as CO₂, H₂O and mineral ions.
The small molecules and ions are released into the surrounding environment, where they are taken up by other organisms, mainly plants, completing the nutrient cycle.
Examiner tips
- Use the word ‘secrete’ for enzyme release, not ‘produce’.
- Show the link between temperature and enzyme activity. Mention moisture as a requirement for decomposers. End with nutrient recycling. Keep each point brief to fit 5 marks.
Common mistakes
- Confusing mould growth with bacterial activity. The question refers to mould (fungi).
- Failing to mention that the bread’s complex molecules are broken down into CO₂, H₂O and mineral ions.
Mark scheme (5 marks)
- Warm temperatures increase the rate of enzyme activity in decomposers
- Damp/moist conditions are needed for decomposers to survive and function
- Decomposers (fungi/bacteria) secrete enzymes onto the bread to break down complex organic molecules
- The organic molecules in the bread are broken down into simpler/smaller molecules (e.g. carbon dioxide, water, mineral ions/nutrients)
- These nutrients/minerals are released back into the environment/soil, recycling them for use by other organisms (e.g. plants)
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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