Question

In the process of apical dominance, lateral buds are unable to grow in the presence of apical bud. This is due to (a) less amount of auxin in apical bud (b) more amount of auxin in apical bud (c) less amount of cytokinins in lateral buds (d) more amount of cytokinins in lateral buds.

Short answer

The correct answer is (b) more amount of auxin in apical bud.

Step-by-step solution

Understanding Apical Dominance

Apical dominance is a phenomenon where the apical bud of a plant inhibits the growth of lateral (side) buds. This helps the plant grow taller rather than wider. The hormone auxin plays a crucial role in this process.

Effect of Auxin

Auxin is produced in the apical bud and is known to inhibit the growth of the lateral buds. A high concentration of auxin in the apical bud suppresses the growth of lateral buds.

Identifying the Correct Option

Based on the understanding that a high amount of auxin in the apical bud is responsible for inhibiting the growth of lateral buds, we can determine that the correct answer is that the presence of more auxin in the apical bud leads to apical dominance.

Key concepts

Auxin

Understanding auxin is crucial for grasping the concept of apical dominance. Auxin is a plant hormone that plays a pivotal role in the growth and development of plants. Produced at the tips of shoots in the apical bud, auxin promotes cell elongation. However, it also has the unique ability to suppress the growth of lateral buds, which are the small shoots found along the stem of the plant.

Auxin diffuses down from the apical bud through the stem, and its higher concentration near the top prevents the lateral buds from sprouting. This mechanism ensures that the plant uses its resources efficiently to extend upwards, seeking sunlight and maximizing its exposure for photosynthesis. It's the delicate balance of auxin concentration which dictates the direction of a plant's growth, making it a central hormone in the plant's response to its environment.

Exercise Improvement Advice

It is essential to highlight the role of auxin concentration in apical dominance, because students often overlook the importance of the hormone's distribution within the plant. Encouraging experiments where auxin is applied to different parts of the plant can also be an effective way to visually demonstrate its effects on plant growth patterns.

Lateral Bud Growth

The process of lateral bud growth is another key aspect of understanding how plants develop their shape and structure. Lateral buds are located at nodes on the plant stem where leaves attach, and they have the potential to grow into branches or flowers. However, in the presence of a dominant apical bud, these lateral buds often remain dormant.

Lateral buds are directly influenced by the levels of plant hormones, such as auxin and cytokinins. When auxin levels are high, lateral bud growth is inhibited; conversely, when cytokinin levels are increased, they can overcome the inhibitory effects of auxin and promote the growth of lateral buds. Thus, the balance between these hormones is vital for the lateral buds to break dormancy and start growing.

Interaction with Environment

Environmental factors such as light, water, and damage to the plant can shift the hormonal balance and therefore impact lateral bud growth. For example, if the apical bud is removed, auxin levels decline, and the lateral buds may be activated, leading to a bushier plant. Students should recognize the significance of environmental interactions in pruning practices and natural damage repair mechanisms in plants.

Plant Hormones

Delving into the world of plant hormones offers insights into how plants coordinate their growth and responses to environmental stimuli. Plant hormones, or phytohormones, are chemical messengers produced in small quantities that have profound effects on plant growth, development, and behavior.

Aside from auxin, plants produce several other hormones such as cytokinins, gibberellins, abscisic acid, and ethylene, each serving unique functions. Cytokinins, for example, promote cell division and are instrumental in the growth of lateral buds. Gibberellins promote stem elongation, seed germination, and flowering, while abscisic acid is crucial for stress responses and dormancy. Ethylene is known for its role in fruit ripening and response to mechanical stress.

Hormonal Harmony

The interplay between these hormones dictates the way a plant will grow and interact with its surroundings. By understanding the specific roles and balance of plant hormones, students can predict how changes in hormone levels can lead to changes in plant appearance and behavior. This understanding is fundamental for agricultural practices, plant breeding, and managing plant health.