# Explain how the structure of phloem tissue is adapted to allow the transport of sucrose throughout a plant.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 2.4 Plant structure and function · Explain · 5 marks

> Plants produce sucrose by photosynthesis in their leaves. This sucrose must be transported to all living cells in the plant, including the roots.

## Mark scheme (5 marks)

1. Phloem contains sieve tube elements / sieve cells that are living cells (with no nucleus at maturity) allowing cytoplasm to be continuous between cells
2. Sieve plates / perforated end walls between sieve tube elements allow sucrose solution to flow through
3. Companion cells provide the energy (ATP) needed to actively load sucrose into the phloem / sieve tube elements
4. Sucrose is transported by translocation from a source (leaves) to a sink (roots / growing regions / storage organs)
5. Phloem can transport sucrose in both directions / up and down the plant, allowing it to reach all living cells

## Key terms

- [phloem](https://www.gradenine.co.uk/glossary/phloem)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-how-the-structure-of-phloem-f879e8ca) · Published by Druglandscape Ltd.