Question

Water is absorbed by root hairs when?

Answer 1

To yield ATP (Adenosine Triphosphate), the root hair in the plant undergoes respiration. In plants, the process of cellular respiration occurs when the glucose breaks down into ATP. Active absorption is the process of movement of water in a plant, following its evaporation from aerial parts like leaf etc.

Complete answer:
Root hairs are a tubular outgrowth of a trichoblast. In other words of epidermal cells of root, they are the lateral extension. They don’t have chloroplasts (they don’t perform photosynthesis) and cuticles (as they hinder water absorption). They have large vacuoles with which they absorb the water quickly and transfer it to the next cell and the salt that is present inside their vacuole speeds up the process of the water absorption. Soil particles trap water between them. The total surface of area for absorption of water increases because the root hairs have extended structure. Between the soil particles by active absorption and passive absorption, from the spaces the root hair being permeable and hydrophilic absorbs the water. Active absorption, the metabolic energy, that in, Adenosine Triphosphate, resulting from respiration is used for absorption of water. In low transpiring and well water plants, the type of absorption occurs can be of two types- Osmotic and Non- osmotic. Atkins in 1916 and Priestley in 1923 given the theory for active osmotic absorption. According to this theory, where the water is absorbed by the xylem present in the root in the presence of concentration gradient, the root cells behave as a typical osmotic pressure system. Thimann in 1951 and Kramer in 1959, gave the theory for non- osmotic active absorption. According to them, the water from the soil absorbed by the xylem present in the root against the concentration gradient. The absorption from the soil to roots occurs in the absence of metabolic energy in passive absorption. It occurs in plants that respire rapidly. Due to transpiration passive absorption occurs.

Note:
The walls of root hair are thin and permeable to water which mix them hydrophilic and their large vacuole helps them to store the absorbed water. The cell wall of the root hair is thinly permeable with a semi-permeable plasma membrane. The minerals like chlorides, nitrides and many more are transferred through root hairs.