What effect do auxins have on plant growth?

• A. They inhibit cell elongation.
• B. They promote root development.
• C. They regulate cell division in roots and stems.
• D. They promote cell elongation and apical dominance.

Answer: (D)

Auxins are a class of plant hormones that significantly influence growth and developmental processes in plants. One of their primary roles is to promote cell elongation in various plant tissues, particularly in stems. This action allows plants to grow taller and stretch toward light sources, an essential process known as phototropism.

In addition to promoting cell elongation, auxins are involved in the phenomenon of apical dominance, where the main central stem grows more significantly than the lateral branches. This dominance is crucial for directing the growth of the plant, allowing it to optimize resources and sunlight capture.

While auxins also play roles in other processes, such as promoting root development and regulating cell division, their most well-established contributions are in fostering elongation and maintaining apical dominance. Thus, the option that encompasses both the promotion of cell elongation and the concept of apical dominance aligns accurately with the fundamental effects of auxins in plant growth.