Problem 120 - Objective Biology for NEET

Question

The transpiration in plants will be the lowest (a) When there is high humidity in the atmosphere (b) High wind velocity (c) There is excess of water in the cell (d) Environmental conditions are very dry

Step-by-Step Solution

Answer

Therefore, the rate of transpiration would be lowest when there is high humidity in the atmosphere, option (a).

Step 1: Evaluate the Options

Understanding how each of these factors impact the process of transpiration is crucial to identify in which condition transpiration would be the lowest.

Step 2: Impact of Humidity

A high level of humidity in the atmosphere increases the water potential outside of the plant. This reduces the amount of water that evaporates from the plant, thus reducing the rate of transpiration.

Step 3: Impact of Wind Velocity

High wind speeds can remove water vapor, causing more water to evaporate from the plant. This would typically increase the rate of transpiration.

Step 4: Impact of Water level in the Cell

An excess of water in the cell also means there is less of a gradient between the inside of the cell and outside, somewhat reducing transpiration, but not to the extent high humidity can.

Step 5: Impact of Dry Environmental Conditions

In very dry environmental conditions, the gradient between the water potential inside the plant and the dry air outside would be large. This would drive transpiration and increase the rate.

Key Concepts

Plant Physiology and Transpiration

Understanding the fundamentals of plant physiology is essential when examining transpiration, the process by which water moves through plants and evaporates from aerial parts such as leaves, stems, and flowers. Within the plant, water is absorbed by the roots from the soil and transported upward through specialized conducting tissues called xylem vessels. This water is crucial for various physiological processes, including photosynthesis, nutrient transport, and temperature regulation.

During photosynthesis, for example, plants use sunlight to convert carbon dioxide and water into glucose and oxygen. A byproduct of this process is the release of water vapor into the atmosphere through tiny pores on the leaf surface known as stomata. Not only is transpiration essential for delivering water to leaf surfaces for photosynthesis, but it also helps to cool the plant on hot days, similar to how sweating cools the human body.

Water Cycle in Plants

The water cycle in plants plays a critical role in their survival and involves multiple processes: absorption, transport, transpiration, and sometimes storage. When studying transpiration, it's important to recognize its place in the plant water cycle. After absorption by the roots, water travels through the plant and eventually reaches the leaves, where transpiration occurs. Here, water vapor exits the leaf through stomata into the external environment.

This movement of water is not solely a passive process; it is closely regulated by the plant. The opening and closing of the stomata are controlled in response to environmental signals. For instance, in low light or high CO2 conditions inside the leaf, stomata tend to close to conserve water. On the other hand, they open wider to maximize gas exchange during optimal light conditions. The transpired water is continually replaced by more water from the soil, maintaining the plant's internal water balance and overall health.

Environmental Factors Affecting Transpiration

Several environmental factors influence the rate of transpiration in plants. Humidity, for instance, plays a significant role. High atmospheric humidity decreases the gradient of water potential between the inside and outside of the leaf, leading to reduced transpiration. Conversely, low humidity increases this gradient, hence boosting water loss through transpiration.

Wind and Transpiration

Wind velocity also affects transpiration. Gentle breezes can remove the humid air around the leaf surface enabling more water to evaporate. However, high wind conditions destabilize this process, as too much wind can close stomata and reduce transpiration rates to prevent excessive water loss.

Water Availability and Transpiration

Water availability within the plant itself is also a factor. Cells saturated with water will have a smaller gradient between their water potential and that of the outside air, which may lower transpiration rates. However, this is less effective than the influence of external humidity. Dry environmental conditions lead to higher transpiration rates due to the steep gradient between the water vapor inside the plant and the dry air outside.