# Explain why carbon dioxide is described as an excretory product in a flowering plant, and describe how it leaves the plant during the hours of darkness.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.12 Excretion: flowering plants · Explain · 4 marks

## Mark scheme (4 marks)

1. Carbon dioxide is a waste product of (aerobic) respiration / produced by metabolism
2. Excretion is the removal of waste products of metabolism from the body / carbon dioxide must be removed as it is a waste product that could be harmful if it accumulated
3. Carbon dioxide moves out of leaf cells / mesophyll cells by diffusion (down a concentration gradient)
4. Carbon dioxide diffuses out of the leaf through open stomata (into the surrounding air / atmosphere)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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