# A scientist is studying how plants transport substances around their bodies. Explain how the structure of phloem tissue is adapted to carry out translocation.

> OCR A-Level Biology B — Advancing Biology (H422) — 2.2 Biological molecules including biochemistry · Explain · 5 marks

> Plants have two main transport tissues: xylem and phloem. Phloem transports sucrose from the source to the sink via translocation. The phloem tissue contains sieve tubes and companion cells.

## Mark scheme (5 marks)

1. Sieve tubes have no nuclei
2. Sieve tubes are connected via their cytoplasms, allowing continuous flow of sucrose
3. Companion cells provide energy for translocation
4. Translocation moves sucrose from source (e.g. leaves) to sink (e.g. roots / growing regions)
5. The absence of a nucleus in sieve tubes leaves more space / room for the transport of sucrose

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-scientist-is-studying-how-plants-03fa34f6) · Published by Druglandscape Ltd.