Name one plant tropism other than phototropism and gravitropism. State the specific stimulus that the plant responds to in this tropism.

Plan an investigation to determine the effect of unilateral light on the direction of growth of germinating plant shoots.

Include details of any control groups and controlled variables needed to ensure a valid investigation.

You may suggest using standard laboratory equipment, such as cress seedlings, Petri dishes, damp filter paper, scissors, cardboard boxes with a small window on one side, and aluminum foil.

Explain how positive phototropism in a plant shoot helps the plant to survive.