Plants are capable of absorbing substances. Plants require water in order to grow and thrive, just as humans do in order to feel and function at their best.
Plants take up water from their surroundings, particularly the soil in which they are rooted, and use it to grow. They achieve this through the use of two different types of absorption: active absorption and passive absorption.
Water Absorption Mechanism
Water is absorbed by higher plants through root hairs that come into contact with soil water and form a root hair zone a short distance 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, the epidermis is also referred to as the piliferous layer). The walls of root hairs are permeable and composed primarily of pectic substances and cellulose, both of which are highly hydrophilic (love water) in their natural environment. Vacuoles filled with cell sap can be found in the root hairs. With elongation of the roots, the older hairs die and new root hairs are produced, allowing the roots to come into contact with fresh water supplies in the soil.
Passive Absorption
The first type of water absorption is passive absorption, which occurs when the rate of transpiration is typically higher than normal. Rapid evaporation of water from the leaves during transpiration causes a buildup of water in the xylem of the leaves, which results in a buildup of pressure. When the water in the xylem of roots is stressed, it rises upward to reach the transpiring surfaces.
As a result, soil water enters the cortical cells through the root hairs and travels to the xylem of the roots, where it helps to maintain the supply of water in the plant. The force necessary for this water entry is generated in the leaves as a result of rapid transpiration, and as a result, the root cells remain passive throughout this process.
It is possible that the flow of water from the epidermis to the endodermis will occur through three different pathways during root absorption of water:
i) Pathway of the apoplastic neoplasm (cell walls and intercellular spaces),
(ii) The transmembrane pathway (which involves crossing the plasma membranes)
iii) Pathway of the Symplast (through plasmodesmata).
In fact, the mechanism of water absorption described earlier falls into the second category of mechanisms. The relative importance of these three pathways in water absorption by roots has not been clearly established in scientific literature. For the transport of water across the root system, a combination of these three pathways is responsible.
Minerals are absorbed in their Passive Forms
Passive absorption is the term used to describe the movement of minerals into cells or tissues without the expenditure of energy. This is a physical phenomenon that has occurred. The following are the methods by which passive absorption occurs:
1. Diffusion
The concentration of ions within the root cells is several times higher than the concentration of ions in the surrounding soil solution. Second, the mineral must pass through a number of barriers before it can enter (the cells of the root). The mineral ions cannot therefore be transported directly from the soil solution into the cells of plant roots through simple diffusion. They can only pass through by diffusion if they are coming from an open area.
The cell wall is the first line of defence. Ions can pass through the cell wall because it is permeable. As a result, they are able to freely pass through it through simple diffusion. After passing through the cell wall, the ions are free to move around. They come across the ectoplast, which is a type of cell membrane. It prevents the movement of ions in the future due to diffusion. It implies that ions can freely move from the soil solution up to this barrier in the soil. When referring to the part of a plant cell or tissue where ions can freely move around by diffusion, the term “free space” is used. It is referred to as apparent free space in some circles (AFS). The ectoplast is the structure that defines the inner boundary of free space. ions enter free space at a very fast rate and do so through a process called diffusion. Ions are also easily dissipated by diffusion.
As a result, ions can diffuse through a free space area, allowing them to pass. This process prevents ions from passing through the ectoplast barrier and entering the protoplasm.
2. Mass Flow (Constant Output)
The movement of ions in conjunction with a large volume of water is referred to as mass flow of ions. Transpiration increases as a result of the increased transpiration, which also increases the absorption of ions from the soil. The role of transpiration in the movement of large amounts of water is explained by the cohesion tension theory. In addition to the mass flow of water, it is believed that mineral ions are also transported into the root system. The effect of transpiration on mineral absorption, according to some physiologists, is an indirect relationship. As a result of transpiration, minerals are removed from the root xylem along with the transpiration stream. As a result, the concentration of the compound in the root cells decreases. A greater amount of minerals are absorbed by the root as a result.
3. Mechanism of Ionic Exchange
An ion exchange reaction is characterised by the exchange of anions or cations from cells with ions of the same and equivalent charge from the surrounding solution. Ion exchange does not necessitate the expenditure of metabolic energy. As a result, it is a passive physical process. As a result, it is not influenced by the rate of aerobic respiration. Have two theories explaining the mechanism of ion exchange have been proposed. The contact exchange theory and the carbonic acid exchange theory are two types of exchange theories.
Conclusion
Water is absorbed by higher plants through root hairs that come into contact with soil water and form a root hair zone a short distance 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, the epidermis is also referred to as the piliferous layer). Passive absorption, which occurs when the rate of transpiration is typically higher than normal. The concentration of ions within the root cells is several times higher than the concentration of ions in the surrounding soil solution.An ion exchange reaction is characterised by the exchange of anions or cations from cells with ions of the same and equivalent charge from the surrounding solution.