# A group of students investigated how auxin controls the growth of plant shoots. They took identical young shoots and treated them as follows: shoot A had auxin applied evenly to both sides of the tip; shoot B had auxin applied only to the right-hand side of the tip; shoot C had its tip removed entirely and no auxin was applied. Explain the pattern of growth you would expect to observe in each of the three shoots after several days.

> Pearson Edexcel A-Level Biology A (9BI0) — 4.7 Plant responses · Explain · 5 marks

> Auxin is a plant hormone produced at the shoot tip. It moves down the shoot and promotes cell elongation. When light strikes a shoot from one side, auxin is redistributed to the shaded side.

## Mark scheme (5 marks)

1. Shoot A grows straight upwards because auxin is distributed equally on both sides, so both sides elongate at the same rate.
2. In shoot B, the side with auxin applied (right-hand side) has more auxin, so cells on that side elongate more / faster.
3. Shoot B therefore bends / curves to the left (away from the side with more auxin / towards the side with less auxin).
4. Shoot C does not produce auxin (because the tip, where auxin is made, has been removed), so little or no cell elongation occurs.
5. Shoot C therefore shows little or no growth and remains upright / does not bend in any direction.

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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/a-group-of-students-investigated-how-f8d866e6) · Published by Druglandscape Ltd.