Problem 108 - Objective Biology for NEET

Question

The chief role of transpiration in plants is to cause (a) Loss of surplus water (b) Cooling of the plant (c) Rapid ascent of sap (d) Rapid rise of minerals

Step-by-Step Solution

Answer

The chief role of transpiration in plants is to cause the rapid ascent of sap.

Step 1: Understanding Transpiration

Transpiration is defined as the process in which water is absorbed by the plant roots from the soil, is transported as a liquid to the leaves via xylem vessels, and is then changed to vapor and evaporated into the atmosphere. This majorly occurs from the leaf surface.

Step 2: Analyzing Options

To solve this, analyze each option against what you've learned about transpiration. A) Loss of surplus water: while plants do lose water through transpiration, this isn’t the primary purpose. B) Cooling of the plant: The evaporation of water cools down the plant, similar to how sweat cools the human body, but isn't their primary purpose. D) Rapid rise of minerals: While water brings minerals from the soil up to the plant, its primary role is still not considered the rise of minerals.

Step 3: Choice Selection

After understanding and analyzing each option, we reach option C) Rapid ascent of sap: The previously ridden water molecules create a pulling force due to cohesion and adhesion properties which assist in the rise of water as sap through the plant - from roots to leaves. This 'pull' or transpiration pull, is the main driver of water movement in plants. Thus, the chief role of transpiration in plants is to cause the rapid ascent of sap.

Key Concepts

Process of water movement in plants

Water movement in plants is a complex yet fascinating process. It starts with the absorption of water from the soil through the plant's roots. This initial step is crucial as the roots act like a sponge, pulling water into the plant structure.
This water is then transported throughout the plant via xylem vessels, acting as tiny pipelines connecting roots to leaves. These vessels ensure that water reaches every part of the plant, providing necessary hydration and nutrients. Water moves upwards through the plant due to various forces. One important force is known as "capillary action," which results from the adhesion and cohesion properties of water molecules. But a significant force driving water movement is the transpiration pull. Understanding this journey of water is key to grasping how plants remain healthy and vibrant.

Functions of xylem vessels

Xylem vessels are essential components in plants, primarily responsible for water and nutrient transport. Composed of long, hollow tubes, they facilitate a streamlined transportation route from the roots to the leaves and other parts of the plant. These vessels serve multiple purposes:

• Transporting water, which is necessary not only for photosynthesis but for maintaining cell structure and function throughout the plant.
• Carrying dissolved minerals from the soil, which are vital for plant growth and development.
• Providing structural support, as xylem vessels are rigid, helping the plant to remain upright.

The structure and durability of xylem vessels ensure they can handle the pressure of the upward pull of water, which makes them indispensable to a plant's survival.

Transpiration pull mechanism

The transpiration pull mechanism is a critical process that facilitates the movement of water from the roots to the leaves of plants. This process capitalizes on water's natural tendency to adhere to the surfaces and cohere to each other. Here's how the transpiration pull works:

• Water evaporates from the leaf surface into the atmosphere in a process known as transpiration. This creates a deficit of water in the leaf's air spaces.
• The loss of water molecules generates a negative pressure gradient within the xylem vessels, known as "transpiration pull."
• This pull helps suck water upward through the plant, similarly to sipping through a straw.

Transpiration pull is an efficient way to move water and essential nutrients against gravity, ensuring that every leaf gets sufficient water to maintain its physiological processes, like photosynthesis and respiration.