# Explain why carbon dioxide produced during respiration in the leaf's palisade mesophyll cells can be used directly for photosynthesis during daylight, without the gas needing to leave the leaf.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.8 Gas exchange: flowering plants · Explain · 4 marks

> During the day, a flowering plant carries out both photosynthesis and respiration simultaneously. The palisade mesophyll and spongy mesophyll are the two main photosynthetic tissues of the leaf.

## Mark scheme (4 marks)

1. Respiration produces carbon dioxide (as a waste gas) inside the palisade mesophyll cells / leaf cells
2. Carbon dioxide can diffuse directly from the respiring cells to the chloroplasts / site of photosynthesis within the same leaf / short diffusion distance
3. Photosynthesis uses / consumes carbon dioxide, maintaining a concentration gradient so carbon dioxide moves from the respiring cells towards the chloroplasts
4. This means the rate of carbon dioxide loss through stomata is reduced / less carbon dioxide needs to be taken in from the atmosphere / the plant is more efficient

## Key terms

- [palisade mesophyll](https://www.gradenine.co.uk/glossary/palisade-mesophyll)
- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-carbon-dioxide-produced-during-168b2490) · Published by Druglandscape Ltd.