5.4 Plant hormones (biology only)

Medium

Some students investigated phototropism in the coleoptiles of oat seedlings using two different setups over 48 hours:

Setup A: 5 coleoptiles pinned to a stationary board with a unilateral light source from the right side.
Setup B: 5 coleoptiles pinned to a board rotating slowly on a motor (clinostat) in front of the same unilateral light source.

The results of the angle of curvature towards the light source (measured in degrees) are shown in the table below:

Coleoptile number	Setup A (Stationary) curvature (°)	Setup B (Rotating) curvature (°)
1	41	2
2	46	1
3	13	3
4	38	0
5	44	2

Explain how the rotating board in Setup B acts as a control.

[2]

Identify the anomalous coleoptile in Setup A and suggest why including its measurement in the mean calculation reduces the validity of the results.

[2]

Calculate a more valid mean angle of curvature for the coleoptiles in Setup A by omitting the anomalous result. Give your answer to 1 decimal place.

[3]

5.4 Plant hormones (biology only) Questions