Problem 114 - Objective Biology for NEET

Question

In a hot summer day, a plant cools itself due to (a) Loss of water vapours from leaf (b) Transport of water in plant (c) Loss of liquid water (d) Loss of water from entire plant

Step-by-Step Solution

Answer

The correct answer is (a) Loss of water vapours from leaf.

Step 1: Understand the Process of Transpiration

Transpiration is the process where plants lose water to the atmosphere. It primarily happens in the leaves through tiny openings known as stomata.

Step 2: Analyze the Options

While the transport of water does occur within the plant (option b), it does not directly result in the plant cooling down. Similarly, the loss of liquid water (option c) and the loss of water from the entire plant (option d) are somewhat imprecise interpretations of the transpiration process.

Step 3: Select the Correct Option

By analyzing each option in the context of the transpiration process, it becomes clear that option (a) loss of water vapours from the leaf, is the most precise and accurate way to describe how plants cool down on a hot day.

Key Concepts

Stomata

Stomata are tiny openings or pores found on the surface of leaves. They play a crucial role in the plant's ability to regulate gases and water exchange with the environment. Stomata are essential for several plant functions:

• Gas Exchange: They allow carbon dioxide to enter the leaf for photosynthesis, and release oxygen as a by-product.
• Regulating Water Loss: By opening and closing, stomata control the amount of water vapor that leaves the plant.
• Cooling Mechanism: Through the process of transpiration, stomata help in cooling the plant.

Each stoma is flanked by two guard cells that control its opening and closing, responding to environmental conditions like light, humidity, and internal plant signals.
By adjusting the stomatal aperture, plants can fine-tune water conservation and gas exchange, optimizing their resources effectively.

Water Vapour Loss

Water vapor loss from plants occurs mainly through the stomata, in a process known as transpiration. This is a critical component of a plant's water regulation strategy:

• Transpiration: The loss of water vapor from the aerial parts of the plant, mainly the leaves. It helps transport nutrients and minerals from the soil to the plant tissues.
• Evaporative Cooling: As water evaporates from the leaf’s surface, it absorbs heat, effectively lowering the plant's temperature.

Transpiration is influenced by external factors like temperature, humidity, and wind. Higher temperatures and wind speeds can increase the rate of water vapor loss, while high humidity can slow it down.
This process not only helps in cooling the plant but also drives the flow of water from the roots to the leaves, ensuring the plant remains hydrated.

Plant Cooling Mechanism

Plants have evolved sophisticated mechanisms to handle high temperatures. Transpiration plays a pivotal role in their cooling system:

• Heat Dissipation: By losing water vapor through the stomata, plants can dissipate excess heat, maintaining a stable internal temperature.
• Maintaining Optimal Photosynthesis Rates: By regulating temperature, plants maintain enzymes and processes involved in photosynthesis at steady and efficient levels.
• Preventing Overheating: Excess heat can damage plant tissues, and through transpiration, plants can prevent such heat damage.

Transpiration is akin to the sweating process in humans; it helps keep the plants from overheating by using evaporative cooling. In this way, the water loss through the stomata not only aids in nutrient transport but is also vital for thermal regulation in plants.