Problem 19 - Biology E/M

Question

Questions \(17-23\) Choose from the terms below. (A) Auxins (B) Gibberellins (C) Abscisic acid (D) Ethylene (E) Cytokinins Enhances apical dominance

Step-by-Step Solution

Answer

(A) Auxins

Step 1: Understanding the Concept of Apical Dominance

Apical dominance is the phenomenon where the main, central stem of the plant is dominant over other side stems. It is primarily controlled by plant hormones.

Step 2: Identifying Plant Hormones Related to Apical Dominance

Among the plant hormones, auxins are known to be responsible for apical dominance. They are produced in the shoot tip and help maintain the dominance of the main stem by inhibiting the growth of lateral buds.

Step 3: Matching the Hormone to the Answer Choices

From the provided options, check which one is related to auxins. The option for auxins is (A) Auxins.

Key Concepts

Auxins

Auxins are a class of plant hormones that play a crucial role in various growth processes within plants. They are primarily synthesized in the shoot tips and can move to other parts of the plant to exert their influence. Here are some key functions of auxins:

• Promotion of cell elongation: Auxins cause cells located in the stem to elongate, which contributes to the plant's vertical growth.
• Root initiation: They are involved in the development of roots from stem cuttings.
• Tropisms: Auxins help plants respond to environmental stimuli such as light (phototropism) and gravity (gravitropism), facilitating the plant's ability to grow towards light sources and maintain balance.

Through chemical signals, auxins regulate and coordinate plant growth and anatomical development. Understanding their role is essential for any discussion relating to plant physiology.

Apical Dominance

Apical dominance is the phenomenon where the main, central stem of the plant inhibits the growth of lateral stems or branches. This process ensures that the plant grows taller and not bushier. Auxins are primarily responsible for this control over plant architecture. They are produced at the tips of the main stem and suppress the growth of lateral buds by maintaining a higher concentration in the apex compared to the sides.

Apical dominance has several advantages for a plant:

• Enhanced access to light: By growing taller, the main stem can reach more sunlight.
• Efficient resource allocation: Energy is directed towards vertical growth, which is beneficial in dense plant communities.
• Adaptability: Plants can alter apical dominance based on environmental conditions, such as when the apical bud is removed or when the plant needs to branch out for survival.

Understanding apical dominance helps in horticulture practices, where manipulating this process can result in desired plant shapes and sizes.

Plant Growth

Plant growth is a complex process influenced by various factors including genetics, environmental conditions, and plant hormones like auxins. Growth occurs primarily through cell division and cell elongation.

The factors affecting plant growth include:

• Light: Plants require light for photosynthesis, which is crucial for producing the energy needed for growth.
• Temperature: Optimal temperature ranges vary for different species, affecting enzymatic activities and metabolism.
• Water: It is essential for maintaining turgor pressure within cells and is a medium for nutrient transport.
• Nutrients: Elements like nitrogen, phosphorus, and potassium are vital for cellular functions and overall plant health.

Hormones such as auxins are key in regulating these aspects by promoting cell elongation and other growth effects, allowing plants to adapt and thrive in varying conditions.