Fig. 3.1 shows four seedlings W, X, Y and Z that have been set up to investigate their response to unidirectional light. W is untreated; X has its tip cut off; Y has its tip covered by an aluminium foil cap; Z has the region below the tip covered with aluminium foil.

1. aDescribe briefly a set up that could be used to ensure that seedlings receive light from one direction. [1]
2. bPredict the appearance of each shoot (W, X, Y, Z) after several days in unidirectional light. [4]
3. cWhich part of the seedling is sensitive to light? [1]
4. dWhat name is given to the growth response to light? [1]
5. eExplain how this growth response is caused. [4]

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