Question

Phenyl mercuric acetate (PMA) results in

• A. reduced photosynthesis
• B. reduced transpiration
• C. reduced respiration
• D. killing of plants.

Answer 1

The Correct Option is B

To solve this question, we need to understand the role and effect of phenyl mercuric acetate (PMA) on plant processes. PMA is a chemical compound often used as a fungicide, bactericide, and herbicide in agriculture.

The options provided are various physiological processes that occur in plants:

• Photosynthesis: The process by which green plants use sunlight to synthesize foods from carbon dioxide and water.
• Transpiration: The process of water movement through a plant and its evaporation from aerial parts like leaves.
• Respiration: The process of converting glucose and oxygen into water, carbon dioxide, and energy.
• Killing of plants: This represents the complete destruction of plant tissues.

PMA is known for its effect of blocking stomatal pores. Stomatal pores are essential for gas exchange and transpiration in plants. By blocking these pores, PMA effectively reduces transpiration.

Explanation:

Transpiration primarily occurs through stomata, which are small openings on the underside of leaves. If a substance like PMA blocks or partially closes these stomata, the transpiration rate reduces as water vapor cannot easily escape.

Here's the reasoning for ruling out other options:

• Reduced photosynthesis: While closing stomata can indirectly impact photosynthesis due to less CO₂ intake, PMA's primary effect is on transpiration.
• Reduced respiration: Stomatal closure primarily affects gas exchange and not directly the cellular respiration rate within plant cells.
• Killing of plants: PMA does not kill plants outright; it primarily affects the transpiration process.

Thus, the correct answer is reduced transpiration.