A student leaves a piece of bread in a warm, moist cupboard. After several days, the bread is covered in mould. The mould is a fungus that secretes amylase onto the surface of the bread to obtain nutrients. Explain how the amylase secreted by the mould allows it to obtain nutrients from the bread, and describe what would happen to the amylase if the temperature in the cupboard became extremely high.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student leaves a piece of bread in a warm, moist cupboard. After several days, the bread is covered in mould. The mould is a fungus that secretes amylase onto the surface of the bread.
Model answer (4 marks)
Amylase is an enzyme that hydrolyses the starch in bread into simple sugars.
The starch molecules have a shape that matches the active site of amylase (lock‑and‑key), so they fit into the site and are cleaved.
The sugars released are then absorbed by the mould as a source of carbon and energy.
If the cupboard temperature becomes extremely high, the amylase will denature – its three‑dimensional structure is permanently altered.
Denaturation destroys the active site so the starch can no longer bind and the enzyme stops working.
The starch molecules have a shape that matches the active site of amylase (lock‑and‑key), so they fit into the site and are cleaved.
The sugars released are then absorbed by the mould as a source of carbon and energy.
If the cupboard temperature becomes extremely high, the amylase will denature – its three‑dimensional structure is permanently altered.
Denaturation destroys the active site so the starch can no longer bind and the enzyme stops working.
Examiner tips
- Use the term ‘enzyme’ and ‘substrate’ – they are key words. Explain the lock‑and‑key model to show understanding of specificity. Mention that denaturation is irreversible and stops catalysis. Keep the answer concise – 4 marks can be earned with 4 short sentences.
Common mistakes
- Confusing the mould with the bread as the source of the enzyme. Saying the enzyme ‘grows’ instead of ‘breaks down’ the starch. Forgetting to state that denaturation is irreversible and stops the reaction.
Mark scheme (4 marks)
- Amylase is an enzyme that breaks down carbohydrates (starch) in the bread into simple sugars
- The substrate (starch/carbohydrate) has a complementary shape to the active site of amylase, so it fits into the active site (lock and key hypothesis)
- At extremely high temperatures, the enzyme denatures
- Denaturation causes a permanent change in the shape of the active site, so the substrate can no longer fit and the enzyme cannot function
Key terms in this question
Related
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