Problem 127 - Objective Biology for NEET

Question

Guttation usually occurs when the plant is put in a (a) More saturated atmosphere (b) More humid soil (c) Dry condition (d) Desert

Step-by-Step Solution

Answer

The correct answer is (a) More saturated atmosphere.

Step 1: Understanding Guttation

Guttation often occurs in plants when the atmosphere is more saturated. This process of water droplets being excreted often takes places during the night or early morning, largely because during these times, the process of transpiration is minimal due to the stomata being closed, while the root pressure is high. Subsequently, excess water is forced out from the hydathodes in the form of liquid droplets.

Step 2: Assess relevance to options

Now, let's examine the answer choices. Guttation does not occur when the plant is in dry condition or desert, as these conditions invoke other physiological responses in the plant like closing of stomata to prevent water loss. Guttation is also not primarily related to the humidity in the soil, but rather to the atmospheric conditions and root pressure.

Step 3: Selecting the correct answer

With the knowledge derived above about guttation and its conditions and after assessing the relevance with the provided options, it is clear that the correct answer is when the plant is placed in a more saturated atmosphere.

Key Concepts

Transpiration

Transpiration is a process vital to plant life, fundamental in understanding guttation. It involves the movement of water within a plant and the subsequent evaporation from aerial parts like the leaves, stems, and flowers. Water is absorbed by plants primarily through their roots and is carried upward through the xylem to various parts of the plant.

During the day, when the stomata (tiny openings on the leaf surface) are open, transpiration rates are high, as the plant releases water vapor into the atmosphere. This release creates a negative pressure within the leaves, aiding in the transport of water and nutrients from the roots. Transpiration serves several functions: it cools the plant, enables upward water and nutrient transport, and maintains a flow of minerals and water from the root to shoot.

Importance of Environmental Conditions

Environmental conditions like temperature, humidity, and wind strongly affect the transpiration rate. In high humidity or cooler temperatures, transpiration decreases because the air already has a high water vapor content or because the temperature differential between the plant and the air is reduced. Thus, understanding the interplay between these environmental variables is crucial for comprehending the transpiration process.

Root Pressure

Root pressure is another central concept in the study of plant water relations, particularly in understanding the phenomenon of guttation. It refers to the osmotic pressure gradient that causes sap to rise through a plant stem to the leaves. This pressure is created when water flows into the roots from the soil, generating a force that helps to drive fluids upward.

The main contributors to root pressure are the active absorption of ions into the root cells from the soil and the osmotic intake of water following those ions. This upward drive is crucial at night when transpiration is minimal because water is not being evaporated from the leaves.

Root Pressure and Plant Health

Significant root pressure generally indicates a healthy root system and sufficient water supply in the soil. However, a lack of transpiration can cause an accumulation of water in the plant, leading to guttation, especially when the surrounding atmosphere is saturated, and evaporation is low. Root pressure can be thought of as a foundational force for the plant's water circulation, complementing transpiration during daylight hours.

Hydathodes

Hydathodes are small structures on the tips or edges of leaves, which play a vital role in the guttation process. They can be thought of as pressure relief valves that release excess water when internal plant pressure gets too high, most notably at night when transpiration is not sufficient to release all the water absorbed by the roots.

These structures are typically located along the leaf margins and appear as tiny pores or openings. Unlike stomata, which can open and close, hydathodes are generally open and are primarily responsible for the release of water rather than gas exchange.

Guttation vs. Dew

It is essential to distinguish between guttation and dew; guttation is an active process caused by root pressure resulting in the exudation of liquid from hydathodes, while dew is condensation of moisture from the air onto the plant surface. Hydathodes are integral to understanding how guttation occurs, especially under conditions of high soil moisture and high atmospheric humidity when other methods of water release like transpiration are less effective.