Answer:
The absorption of water and mineral salts from the soil by root hairs involves several physiological processes. Here are the main steps involved:
Osmosis: Root hairs create a concentration gradient by actively transporting mineral salts into their cells from the soil. This increases the solute concentration inside the root hairs. As a result, water moves into the root hairs by osmosis from an area of lower solute concentration (soil) to an area of higher solute concentration (root hairs).
Active transport: Root hairs actively transport mineral salts from the soil into their cells against the concentration gradient. This process requires energy in the form of ATP. Active transport mechanisms, such as proton pumps, help in the uptake of specific mineral ions, such as potassium, calcium, and nitrate.
Diffusion: After mineral salts are absorbed into the root hairs, they move through the root cortex by diffusion. Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. Mineral salts diffuse across cell membranes and move toward the xylem vessels present in the center of the root.
Capillary action and cohesion-tension theory: Once the water and mineral salts reach the xylem vessels in the root, they are transported upwards through the plant by capillary action and cohesion-tension theory. Water molecules form a continuous column due to their cohesive properties, and as water evaporates from the leaves through transpiration, a negative pressure or tension is created, which pulls the water column upwards.
These physiological processes, including osmosis, active transport, diffusion, capillary action, and cohesion-tension theory, work together to facilitate the absorption of water and mineral salts from the soil by root hairs and their subsequent transport throughout the plant via the xylem vessels.