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

How does phototropism affect the direction of plant growth?

1. It causes uniform growth in all directions

2. It optimizes light exposure for photosynthesis

3. It reduces plant height for better stability

4. It restricts root growth to certain areas

The correct answer is: It optimizes light exposure for photosynthesis

Phototropism is the growth response of plants to light direction, primarily facilitated by the hormone auxin. When a plant is exposed to light from one direction, auxin accumulates on the side of the plant that is away from the light. This unequal distribution of auxin promotes faster growth on the shaded side, causing the plant to bend towards the light source. This adaptation optimizes the plant's light exposure, enhancing photosynthesis efficiency, as plants rely on sunlight to produce their food. The other options do not accurately describe the effects of phototropism. While uniform growth in all directions would not allow for effective light absorption, reducing plant height does not directly relate to phototropic responses, which primarily influence directional growth rather than overall height. Lastly, phototropism specifically pertains to the aerial parts of the plant in response to light; it does not restrict root growth, which is influenced by gravitropism and other factors.