# Explain why water vapour is considered a waste product of metabolism in a flowering plant and describe how it is removed from the plant.

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

## Mark scheme (4 marks)

1. Water is produced as a waste product during aerobic respiration (in the mitochondria) / water is a by-product of metabolic reactions
2. Excess water (vapour) must be removed / it is excreted because it cannot be stored / it would be harmful if it accumulated
3. Water vapour diffuses out through the stomata (in the leaves) / moves down a concentration gradient from inside the leaf to the atmosphere
4. Water vapour can also be lost through the lenticel(s) in stems / through the cuticle (though the waxy cuticle reduces this loss)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
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