Mechanism of water absorption

Water is absorbed by higher plants through root hairs that come into contact with soil water and form a root hair zone a little behind the root tips. Root hairs are tubular hair-like prolongations of the cells of the epidermal layer of the roots (when the epidermis bears root hairs, it is also known as the piliferous layer). 

The walls of root hairs that are permeable and the made up of pectic substances and the cellulose, both of which are highly hydrophilic (love water). Vacuoles filled with cell sap can be found in root hairs.

When roots grow longer, older hairs die and new root hairs emerge, allowing them to be in contact with fresh water supplies in the soil.

Mechanism of water absorption in plants

Water absorption in plants is a biological process in which plants transport capillary water from the soil to the root xylem via root hairs during various plant processes such as respiration, transpiration, and osmosis. Water supply is an important factor that influences all plant activities such as photosynthesis, internal water balance, and so on.

Water loss in plants can cause leaf wilting, stomatal closure, a reduction in photosynthetic activity, and protoplasm disorganisation. In plants, absorbed water usually exists in two phases: apoplastic water and symplastic water. Apoplastic water is found in the cell wall and xylem, whereas symplastic water is found in the cell protoplast.

Types of water absorption in plants

Plants typically absorb water in one of two ways:

• Active absorption of water
• Passive absorption of water

Active absorption of water

This type of water absorption necessitates the use of metabolic energy by root cells to perform metabolic activities such as respiration. Water absorption occurs in two ways in plants: osmotic absorption and non-osmotic absorption.

1. Osmotic active absorption of water: This type of water absorption occurs via osmosis, with water moving into the root xylem across the concentration gradient of the root cell. Because of the high concentration of solute in the cell sap and the low concentration of the surrounding soil, osmotic movement occurs.
2. Non-osmotic active absorption of water: Water absorption occurs here when water enters the cell from the soil against the cell’s concentration gradient. This necessitates the use of metabolic energy via the respiration process. As a result, as the rate of respiration increases, so will the rate of water absorption. Auxin is a growth hormone that increases the rate of respiration in plants, which increases the rate of water absorption.

Passive absorption of water

The use of metabolic energy is not required for this type of water absorption. Absorption occurs as a result of metabolic activity such as transpiration. Passive absorption is the type of water absorption that occurs as a result of transpiration pull. This creates tension or force, which aids in the upward movement of water into the xylem sap. The higher the transpiration rate, the greater the water absorption.

Role of Root Hairs in Water Absorption

Root hairs are tubular, hair-like, unicellular structures found in roots. The region of the root system from which the root hairs protrude is known as the Root hair zone. The only region that participates in water absorption activity is the root hair zone. The water-permeable zone is the root hair zone. Root hairs are outgrowths from the epidermal layer known as the piliferous layer.

The cell wall of root hair is made up of two layers of membrane. The outer layer of the cell wall contains pectin, while the inner layer contains cellulose. A selectively permeable cytoplasmic membrane exists beneath the cell wall. Specific substances will be allowed to pass through the cell or cytoplasmic membrane across the cell concentration gradient.

Inside the cytoplasmic membrane are root cells, nucleus, and vacuole or cell sap. Soil aggregates contain small droplets of water that are carried away by the root hairs into the root xylem via various mechanisms, the most common of which is osmosis.

Factors Affecting of Water absorption

There are two types of factors that influence the activity of water absorption, either directly or indirectly.

• Extrinsic factors include: It includes external or environmental factors such as:
• Soil water: The soil contains five different types of water, one of which is capillary water, which is essential for the plant’s biological activity.
• The soil solution concentration: The soil solution concentration must be less. When there is a high concentration of soil, it is referred to as physiologically dry soil. Water absorption is hampered by highly concentrated or dry soil.
• Soil air: For proper air supply, there should be space between soil particles. If the amount of oxygen is reduced, the amount of carbon dioxide increases, resulting in anaerobic respiration.
• Temperature of the soil: The ideal temperature is between 20 and 35 degrees Celsius.
• Intrinsic factors: Intrinsic factors include metabolic activities such as respiration, transcription, and the number of root hairs, which all have a direct impact on the rate of water absorption.

Conclusion

Water absorption in plants is a biological process in which plants transport capillary water from the soil to the root xylem via root hairs during various plant processes such as respiration, transpiration, and osmosis. Active absorption of water necessitates the use of metabolic energy by root cells to perform metabolic activities such as respiration Active absorption of water  occurs via osmosis, with water moving into the root xylem across the concentration gradient of the root cell. Because of the high concentration of solute in the cell sap and the low concentration of the surrounding soil, osmotic movement occurs. Auxin is a growth hormone that increases the rate of respiration in plants, which increases the rate of water absorption.