Problem 128 - Objective Biology for NEET

Question

Guttation is the process of elimination of water from plants. It occurs from the pores in leaves through which water comes out in the form of droplets or a specialized multicellular structure in leaves which excretes water droplets. The pores are called (a) Stomata (b) Hydathodes (c) Lenticels (d) Wounds

Step-by-Step Solution

Answer

The correct answer is (b) Hydathodes.

Step 1: Understand the given options

Review each of the given options and determine what each term means. Stomata are small openings on the surface of leaves used for gas exchange. Hydathodes are specialized cells on leaf tips for water expulsion. Lenticels are porous tissue that allow for gas exchange in woody plants. Wounds here refer to any form of injury or cut on the plant's surface.

Step 2: Comparing the functions of the given options

Compare the functions of the given options with the process described in the problem. The question refers to the expulsion of water in the form of droplets from leaves, a process known as guttation. Guttation typically happens through specific structures designed for this purpose.

Step 3: Select the correct option

From the comparison in step 2, it can be seen that Hydathodes serve the function described in the question. Stomata are primarily for gas exchange, not water expulsion. Lenticels serve a similar purpose but are found in woody plants, not leaves. Wounds aren't specialized structures, but accidental openings. Hence, the correct choice is Hydathodes (b).

Key Concepts

Hydathodes

Hydathodes are the exit points on the leaves of many plants where guttation takes place. The process of guttation involves the release of excess water through these structures, usually found along the edges or tips of the leaves. These are not to be confused with stomata, as hydathodes are specifically adapted for the exudation of water droplets, which can be observed in the early morning as tiny beads on the leaf's edge.

• Function: The main role of hydathodes is to release water under high humidity or when roots absorb more minerals creating a pressure that pushes the water out.
• Structure: Unlike stomata, hydathodes are open permanently, allowing them to exude moisture regardless of external conditions.

Understanding hydathodes helps students grasp why plants sometimes 'weep,' which shows the intricacy and adaptability of plant physiology.

Stomata

Stomata are another type of small opening on the plant's epidermis, predominantly found on the underside of leaf surfaces. Their main function is to facilitate gas exchange between the plant and its environment. During photosynthesis, stomata open to allow carbon dioxide to enter and oxygen to exit the leaf. Additionally, they aid in regulating water loss via transpiration.

• Operation: Stomata consist of two guard cells that swell or shrink to open or close the pore, responding to environmental signals.
• Significance: The ability to open and close makes stomata crucial for maintaining water balance within the plant while allowing the necessary exchange of gases.

When discussing guttation, it's important to differentiate it from transpiration, which is controlled by the stomata and not involved in liquid water expulsion.

Lenticels

Lenticels serve as an essential component for gas exchange in woody plants. They appear as rough, cork-like spots on the bark and stem surfaces of trees and shrubs. Students can understand these structures as the breathing system for the woody parts of a plant.

• Purpose: Lenticels allow oxygen to diffuse into the plant for respiration, and carbon dioxide to diffuse out.
• Adaptations: They are adapted to open and expose more surface area in response to increased metabolic demand for oxygen.

Highlighting the ecological importance, lenticels ensure the survival of woody plants, especially where the stomata are not present or cannot adequately serve the gas exchange needs of the plant.

Plant Water Expulsion

Plant water expulsion is an interesting phenomenon wherein excess water is ejected from the plant through different mechanisms, guttation being a prime example. It is a plant's way of balancing its internal water pressure and is often mistaken as dew.

• Environmental Trigger: Typically occurs during the night or early morning when soil moisture levels are high, but transpiration is low.
• Mechanism Variety: While hydathodes are key for guttation, plants also lose water through transpiration via stomata and, to a lesser extent, through lenticels.

Understanding the diverse methods of water expulsion aids students in differentiating between the processes and their roles in overall plant health and water regulation.