Question

The transpiration is regulated by the movements of (a) Subsidiary cells of the leaves (b) Guard cells of the stomata (c) Mesophyll tissue cells (d) Epidermal cells of the leaves

Short answer

The correct answer is (b) Guard cells of the stomata.

Step-by-step solution

Understand the Terminology

Before answering, one has to understand the terms used. Transpiration is the process where water is transferred from the roots to leaves, and evaporates into the atmosphere. Different cells named in the options have a variety of responsibilities in the plant.

Evaluate Each Option

Evaluate every option given, based on the properties and the known functions of the cells named therein. (a) Subsidiary cells - these are specialized cells found in the leaf tissues, but they do not directly regulate transpiration. (c) Mesophyll tissue cells - these are a type of ground tissue that makes up most of the interior of plant leaves and are mainly responsible for photosynthesis. They have no major role in transpiration regulation. (d) Epidermal cells of the leaf - while epidermal cells help form the protective outer layer on the leaf surface, they do not actively regulate transpiration.

Select the Correct Option

By a process of elimination, and by confirming with knowledge of plant cell functions, we see that (b) Guard cells of the stomata regulate the process of transpiration. Stoma are small openings on the leaf surface for gas exchange, and the guard cells control these openings’ size which affects transpiration rate.

Key concepts

Guard Cells

Guard cells play a vital role in the process of transpiration. They are specialized plant cells found on leaves, surrounding the small openings known as stomata. These cells are typically bean-shaped and work in pairs. Their main function is to control the opening and closing of the stomata, which are crucial for the process of transpiration.

Transpiration involves the movement of water from the plant's roots, traveling upward through the stem and reaching the leaves where it evaporates into the atmosphere. This movement also helps in nutrient transport within the plant. The guard cells regulate this by altering the stomatal size.

• When the plant has ample water, guard cells take up water and become turgid, causing the stomata to open, which increases transpiration.
• Conversely, during water scarcity, guard cells lose water and become flaccid, thereby closing the stomata and reducing water loss.

Guard cells are sensitive to environmental factors such as light, carbon dioxide levels, and humidity, adjusting their function to meet the plant's needs.

Stomata

Stomata are tiny openings or pores located primarily on the underside of plant leaves. These structures are essential for gas exchange, allowing the plant to take in carbon dioxide from the atmosphere for photosynthesis and release oxygen as a byproduct.

The stomata are pivotal in the regulation of water loss through transpiration. During this process, water vapor exits the plant through these openings. The size of the stomata can influence the rate of transpiration significantly.

• Open stomata allow for the maximum exchange of gases and release of water vapor, facilitating high rates of transpiration.
• Closed stomata limit this exchange, conservatively managing the plant's water resources during dry conditions.

By controlling the stomatal aperture, the plant can balance its need for carbon dioxide with its water retention requirements, crucial for survival in varying environmental conditions.

Plant Cell Functions

Plant cells exhibit diverse functions that contribute to the overall health and growth of the plant. Beyond the specialized guard cells and stomata, various cell types play specific roles in plant physiology.

• Subsidiary cells: These provide structural support to guard cells and contribute indirectly to stomatal function.
• Mesophyll cells: Found in the leaves, they are primarily involved in photosynthesis, converting sunlight into chemical energy.
• Epidermal cells: These form the plant's outer skin, protecting it against physical damage and pathogens while minimizing water loss.

Each cell type works synergistically to ensure the plant efficiently performs functions critical for survival and adaptation. These include photosynthesis for energy production, respiration for energy release, and homeostasis for stable internal conditions, alongside mechanisms like transpiration for nutrient and water movement.