Problem 195 - Objective Biology for NEET

Question

Assertion: Trichomes helps in preventing water loss due to transpiration. Reason: On the stem, the epidermal hairs are called trichomes.

Step-by-Step Solution

Answer

Both the assertion and reason are correct, but the reason does not fully explain the assertion.

Step 1: Verify the Assertion

First, check the validity of the assertion. Trichomes, indeed, play a role in reducing the rate of water loss from plants by transpiration.

Step 2: Verify the Reason

Then verify the reason. Trichomes are indeed epidermal hairs found on the aerial parts of the plants like stems and leaves, which corroborates the second statement.

Step 3: Link Assertion and Reason

Lastly, it has to be ascertained if the reason is the correct explanation for the assertion. The reason does provide a partial explanation about what trichomes are but it doesn’t explain how they prevent water loss due to transpiration. Trichomes prevent water loss by creating a thicker layer over the surface of plants, which reduces the rate of transpiration. Therefore, while both statements are correct, the reason does not fully explain the assertion.

Key Concepts

Transpiration

Transpiration is a natural process whereby plants lose water in the form of vapor from small pores, known as stomata, on their leaves and stems. This process is vital for plants because it helps with nutrient absorption, temperature regulation, and photosynthesis. However, excessive transpiration can lead to water loss, stressing the plant, especially in dry or hot conditions. Understanding how plants manage transpiration can provide insights into their survival strategies in different environments.

If plants lose too much water through transpiration, they can wilt and eventually die. Therefore, plants have evolved various adaptations to minimize water loss, including the presence of epidermal hairs known as trichomes. These adaptations play a crucial role in maintaining the plant's water balance and overall health.

Epidermal hairs

Epidermal hairs, or trichomes, are small hair-like structures found on the surface of plants' aerial parts such as leaves and stems. These fine projections serve several functions, including defense against herbivores and pathogens, and reducing water loss. Trichomes vary greatly in their structure and function depending on the plant species.

They act as a physical barrier against environmental factors, such as wind and heat, that can exacerbate water evaporation from plant tissues. Additionally, they can trap humidity close to the plant surface, reducing the water vapor gradient and thus slowing down the rate of transpiration. By doing so, epidermal hairs help plants conserve water, which is crucial for survival in arid environments.

Water loss prevention

Preventing water loss is essential for plant health, particularly in regions prone to drought or high temperatures. Plants employ various mechanisms to reduce water loss, ensuring their survival and growth. One such mechanism is the development of trichomes on the surfaces of leaves and stems.

​Trichomes help prevent water loss by increasing the boundary layer resistance, which refers to the thin layer of still air that lies over the plant surface. This reduces the velocity of air movement, thereby decreasing evaporation. Additionally, they reflect a portion of the sun’s radiation, lowering the surface temperature of the leaves and reducing the rate of transpiration.

• By creating a microclimate near the plant surface, trichomes help retain moisture.
• They also serve as a deterrent to herbivores, indirectly supporting water retention by reducing leaf damage.

Implementing these traits shows how plants have adapted structurally to combat environmental pressures related to water loss.