Problem 132 - Objective Biology for NEET

Question

Select from the following (in numbers) the correct function which are performed by transpiration. (1) Creates transpiration pull for absorption and transport of water in plant. (2) Transport minerals from the soil to all parts of the plant. (3) Cools the leaf surface (sometime \(10-15^{\circ} \mathrm{C}\) ). (4) Supplies water for photosynthesis. (5) Maintains the shape and structure of plants by keeping the cells turgid. (a) 1 (b) 3 (c) 4 (d) 5

Step-by-Step Solution

Answer

All the options (a, b, c, d) which represent functions 1, 3, 4 and 5 are correct as they all are functions performed by transpiration in plants.

Step 1: Understand Transpiration

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. This process has multiple functions in a plant.

Step 2: Evaluate Each Statement

(1) One of the primary functions of transpiration is to create a pull (Capillary action) that helps in the absorption and transport of water from the roots to different parts of the plant. (2) Transpiration also assists in transporting minerals from the soil to all parts of the plant dissolved in the water. (3) The evaporation of water from plant surfaces causes a cooling effect, reducing leaf temperature. (4) Water supplied through transpiration is a vital component in the process of photosynthesis. (5) Keeping cells turgid and maintaining the structure of plants is another significant function of transpiration.

Step 3: Select Correct Options

By evaluating the statements, all five functions (1, 2, 3, 4, 5) are performed by transpiration in plants. Thus, all the provided options (a, b, c, d) are correct.

Key Concepts

Transpiration Pull

Transpiration pull is a remarkable phenomenon in the plant kingdom, serving as an essential vehicle for water transport in plants. Think of it as a natural pump, powered by the evaporation of water from the leaves and other aerial parts of a plant. As water molecules are lost to the atmosphere, a negative pressure is created within the plant’s xylem—the long tubes transporting water from the roots to the leaves. This negative pressure or 'pull' draws water upward from the roots, defying gravity in an impressive display of natural physics.

Understanding this invisible force requires an appreciation of cohesion and adhesion—two key properties of water. Cohesion keeps water molecules attracted to each other, facilitating the movement of water in a continuous column through the xylem. Adhesion, on the other hand, helps the water column adhere to the sides of the xylem vessels, crucial for maintaining the flow during transpiration pull.

Think of transpiration pull as the driver behind a plant's internal water elevator, essential for life and growth.

Water Transport in Plants

Water movement within plants operates on a sophisticated transportation plan. Beyond transpiration pull, plants employ a network of cells and vessels to ensure that hydration reaches from root to leaf tip. The xylem, mentioned earlier, functions like highways for water transport, channeling H2O and nutrients picked up from the soil.

Pathways of Water

Water in plants follows two main pathways: the apoplast and symplast routes. In the apoplast route, water moves outside the cell membranes, slipping through spaces between cells, while in the symplast route, it travels within the continuity of cytoplasm of cells interconnected by plasmodesmata. These routes work simultaneously to maintain a steady flow, reflecting the plant’s sophisticated water management system.

Understanding the process fully helps us grasp not only how plants nourish themselves but also their role in maintaining ecological water cycles.

Plant Cooling Mechanism

The cooling effect that transpiration brings to plants is akin to human sweating—a built-in air conditioning system during hot temperatures. As water evaporates from the surface of leaves, it consumes heat energy from the surrounding environment to change from liquid to vapor. This process leads to a significant cooling effect, with leaf temperatures sometimes dropping as much as 10-15°C below the ambient temperature.

The delicate ballet of opening and closing stomata—pores on the leaf surface—regulates this cooling process. When temperatures soar, stomata generally open wider to release more water vapor, thus enhancing the cooling effect. This biological thermostat helps to protect the plant from overheating and keeps cellular activities operating efficiently despite external heat stress.

Photosynthesis Water Supply

Water becomes the lifeblood of photosynthesis—the process that plants use to convert light energy into chemical energy. It’s involved at the very core of the photosynthetic equation where light, carbon dioxide, and water join forces to create glucose and oxygen. Transpiration's task is ensuring a constant supply of water to meet the relentless demands of photosynthesis.

Vital Ingredients

In the grand recipe of photosynthesis, water is split within the chloroplasts, releasing oxygen as a byproduct. This step, called photolysis, is vital to sustaining life on earth, not just for the plant but also for the oxygen-dependent creatures. Hence, transpiration is critical for keeping the photosynthetic machinery well-oiled and functioning smoothly.

Turgidity in Plant Cells

Turgidity refers to the firmness of plant cells that is chiefly maintained by water pressure inside the cell walls, known as turgor pressure. When cells are fully plumped up with water, they become turgid, providing structural support to the plant. This is akin to blowing air into a balloon; the turgor pressure gives plants their upright stance and helps maintain their shape.

Transpiration not only aids in water transport and cooling but also plays a guardian role in sustaining cell turgidity. As plants lose water through transpiration, uptake from the roots typically compensates for this loss. A delicate balance must be upheld—if too much water escapes and isn't replaced, the cells become flaccid and the plant wilts, illustrating the critical role of transpiration in maintaining plant health and vitality.