# A student leaves a piece of bread in a warm, moist cupboard. After two weeks, the bread is covered in mould and has significantly decreased in mass. Explain why the bread decreases in mass over the two weeks.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.5 Decomposition and decay · Explain · 5 marks

> Decomposers, including fungi and bacteria, break down organic material through a series of biological processes. The rate of decomposition is affected by temperature, moisture and oxygen availability.

## Mark scheme (5 marks)

1. The mould (fungi) / bacteria are decomposers that feed on / break down the bread
2. Decomposers release enzymes onto / into the bread (extracellular digestion) to break down complex organic molecules
3. The soluble products / simple molecules are absorbed into the decomposer for use in respiration / growth
4. Carbon dioxide and water are released as waste products of (aerobic) respiration
5. Loss of carbon (as CO₂) / loss of organic material to the decomposers means the mass of the bread decreases

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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