Plant Hormones — Set 5
Biology · पादप हार्मोन · Questions 41–50 of 50
Which hormone is primarily responsible for the expansion of cells in the stem?
Correct Answer: A. Auxin
Auxins increase the plasticity of the cell wall, allowing the cell to take in more water and expand. This process is fundamental to the overall growth in height of the plant. It works through the activation of proton pumps in the cell membrane.
Which of the following hormones is associated with the 'opening' of stomata?
Correct Answer: B. Cytokinin
Cytokinins generally promote the opening of stomata and can counteract the effects of abscisic acid. They help maintain the turgidity of guard cells under normal conditions. This balance regulates the exchange of gases for photosynthesis.
Which plant hormone is often associated with the 'malting' of barley in the beer industry?
Correct Answer: B. Gibberellin
Gibberellins are applied to barley seeds to trigger the production of enzymes that convert starch into sugar. This process is essential for providing the fermentable sugars needed for brewing. It ensures a high-quality and consistent product.
Which hormone is primarily responsible for the growth of 'lateral' buds in a plant?
Correct Answer: A. Cytokinin
Cytokinins promote the growth of lateral branches by overcoming the inhibitory effect of auxins from the tip. If the shoot tip is removed, cytokinin levels in the lateral buds rise, making the plant bushy. This is the physiological basis of pruning.
Which hormone is used to thin out excess flowers and fruits in commercial orchards?
Correct Answer: B. Ethylene
Applying ethylene can cause some flowers or small fruits to drop, leaving more resources for the remaining ones. This results in larger and higher-quality fruits at the time of harvest. It prevents the tree from becoming overloaded and breaking branches.
Which plant hormone is chemically an adenine derivative?
Correct Answer: D. Cytokinin
Cytokinins are structurally similar to the nitrogenous base adenine found in DNA and RNA. This chemical similarity is related to their role in stimulating cell division. Both natural and synthetic cytokinins share this basic structure.
Which hormone is responsible for 'senescence' or the biological aging of plant parts?
Correct Answer: B. Ethylene
Ethylene promotes the aging of leaves and flowers by triggering the breakdown of proteins and pigments. This is a natural part of the plant's life cycle as it prepares for dormancy or reproduction. Cytokinins act as the primary antagonist to this process.
Which hormone is synthesized in the 'root cap' to perceive gravity?
Correct Answer: A. Auxin
The root cap contains specialized cells that detect gravity and redistribute auxin accordingly. This ensures that the root always grows downward into the soil. This response is known as positive geotropism.
Which hormone is responsible for the 'shaking' or falling off of citrus fruits during harvest?
Correct Answer: A. Ethylene
Ethylene promotes the weakening of the fruit stalk, making it easier to harvest fruits like oranges and lemons mechanically. It is often sprayed on trees just before the harvest date. This reduces the manual labor required and speeds up the collection process.
Which hormone is primarily involved in the differentiation of vascular tissues (xylem and phloem)?
Correct Answer: C. Auxin
Auxin is a key regulator in the development of the plant's plumbing system. It directs the formation of new xylem and phloem cells as the plant grows. This ensures that the plant can transport water and nutrients effectively to all parts.