Texas FFA Nursery Landscape Practice Exam

What is the role of auxins in plant growth?

1. A. They promote lateral bud growth

2. B. They stimulate root formation

3. C. They inhibit leaf drop

4. D. They promote apical growth and inhibit lateral growth

The correct answer is: D. They promote apical growth and inhibit lateral growth

Auxins are a class of plant hormones that play a crucial role in regulating growth and development. They are primarily produced in the apical meristem, which is located at the tips of shoots and roots. One of their key functions is to promote apical growth, which means they encourage the elongation of the main shoot, allowing the plant to grow taller and reach towards light sources. In addition to promoting upward growth, auxins have an inhibitory effect on lateral (side) growth. This phenomenon is known as apical dominance, whereby the presence of auxins from the main shoot suppresses the growth of lateral buds, ensuring that the plant prioritizes height and light access over the development of side shoots. This helps the plant allocate resources effectively, enabling it to optimize its growth conditions. The other options, while relevant to plant growth, do not encapsulate the primary function of auxins as accurately. Lateral bud growth typically occurs when auxins decrease in concentration, which does not align with the role of auxins in promoting apical growth. Similarly, while auxins can influence root formation and the regulation of leaf drop, their most defining role is the promotion of apical growth along with the inhibition of lateral growth.