Mastering Growth Control Quiz Quiz

Explore key concepts in plant growth regulation for horticulture, focusing on hormones, environmental factors, and their practical applications in agriculture.

1. Role of Auxins in Plant Growth

   Which function is most commonly associated with the plant hormone auxin in horticultural crops, such as tomatoes or apples?

   1. Enhancing fruit coloration
   2. Promoting cell elongation
   3. Increasing root nodule formation
   4. Stimulating seed dormancy

   Explanation: Auxins primarily promote cell elongation, which is vital for plant growth and directional responses like phototropism. While some hormones like gibberellins influence seed dormancy and cytokinins may impact root nodules, auxins do not directly enhance fruit coloration. Thus, promoting cell elongation is the most accurate answer.

2. Ethylene and Fruit Ripening

   In controlling the timing of fruit ripening in horticulture, which plant hormone is typically applied to trigger ripening in crops like bananas or tomatoes?

   1. Gibberellin
   2. Abscisic acid
   3. Ethylene
   4. Zeatin

   Explanation: Ethylene is widely used to regulate and synchronize fruit ripening in commercial horticulture. Abscisic acid is more involved in stress responses and seed dormancy, gibberellins promote stem growth, and zeatin is a type of cytokinin linked to cell division rather than ripening.

3. Pruning and Plant Hormones

   Why does removing the shoot apex (apical bud) of a horticultural plant often lead to increased growth of lateral branches?

   1. It increases ethylene synthesis in roots
   2. It enhances abscisic acid levels in buds
   3. It reduces auxin production at the tip
   4. It limits cytokinin transport to leaves

   Explanation: The shoot apex produces auxins, which suppress lateral bud growth—a phenomenon known as apical dominance. Removing the apex reduces this auxin, allowing lateral branches to develop. Increased ethylene synthesis, altered cytokinins, or abscisic acid are less relevant to this direct effect.

4. Environmental Influence on Growth Regulators

   How can controlled environmental factors in greenhouses influence endogenous plant growth regulator activity?

   1. Light duration alters hormone production
   2. Pruning always decreases gibberellin
   3. High humidity inactivates auxins
   4. Root pruning boosts xylem flow

   Explanation: Manipulating light in greenhouses, such as changing day length or intensity, can affect activities of hormones like gibberellins and cytokinins. Root pruning affects water/nutrient uptake, not directly hormones, while pruning doesn't always reduce gibberellin, and high humidity does not inactivate auxins.

5. Use of Growth Retardants

   What is the main horticultural purpose of applying growth retardants, such as paclobutrazol, to ornamental plants?

   1. To produce more compact plants
   2. To induce early fruit drop
   3. To improve seed germination
   4. To accelerate flowering

   Explanation: Growth retardants slow stem elongation, resulting in compact, manageable ornamental plants. They do not accelerate flowering, cause early fruit drop, or directly improve seed germination, making compact growth the correct application.