OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What role do auxins play in plants?

1. They regulate photosynthesis

2. They control growth at the tips of shoots and roots

3. They facilitate water absorption

4. They protect against pests

The correct answer is: They control growth at the tips of shoots and roots

Auxins are a class of plant hormones that primarily play a crucial role in the regulation of growth at the tips of shoots and roots. They influence various growth processes, including cell elongation, which allows plants to grow towards light sources (a response known as phototropism) and to explore their environment through root growth. The ability of auxins to affect the direction and rate of growth makes them essential for the overall development of plants. For instance, when a plant is exposed to light from one side, auxins accumulate on the shaded side, promoting cell elongation in that area. This causes the plant to bend towards the light, optimizing its ability to perform photosynthesis. Additionally, auxins also play a part in the formation of lateral roots and the regulation of fruit development and ripening. While the other options may touch upon important functions in plant physiology, they do not align with the primary role of auxins. For example, photosynthesis regulation involves other biochemical processes, water absorption is influenced by root structure and other hormones, and pest protection mechanisms often relate to other plant defenses, not auxins directly. Hence, the role of auxins is specifically associated with controlling growth at the tips of shoots and roots.