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

What effect does auxin have on the growth of roots?

1. Stimulates growth

2. Inhibits growth

3. No effect on length

4. Only affects lateral roots

The correct answer is: Inhibits growth

Auxin is a plant hormone that plays a crucial role in the growth and development of plants, particularly in regulating plant response to gravity and light. In the case of root growth, auxin behaves differently compared to its effect on shoots. Auxin concentrations are typically higher on the side of the root that is exposed to lower light or gravity, which leads to asymmetrical growth. This differential growth results in the inhibition of growth on the side with higher auxin concentration, causing the root to bend and grow towards gravity (positive geotropism). Thus, auxin inhibits the growth of roots primarily by slowing down cell elongation on the side where it is more concentrated. This action is essential for the plant to maintain proper orientation and to ensure stability, as well as optimal nutrient and water uptake from the soil. Therefore, the understanding of auxin's role as an inhibitor of root growth is vital in the context of plant biology.