Water as a Plant Component

1. Water as a plant component The active physiological state in an individual cell and all cells in a plant depends on several relatively constant conditions, one of which is water balance. Once upon a time, during its development, a plant lacks a water supply, then the water content in the plant decreases and the rate of development, which is determined by the rate of all vital functions, also decreases. Prolonged drought conditions can kill plants. Diffusion is a physical process, which can occur every day in nature and in plant life or other organisms. Diffusion occurs as a response to differences in concentration. A difference occurs when there is a change in concentration from one state to another. Apart from differences in concentration, there are differences in properties can also cause diffusion. The process of gas exchange in plants that occurs in leaves is an example of a diffusion process. In this process CO gas2from the atmosphere into the intercellular cavities in the leaf mesophyll, which are then used for the process of photosynthesis. Osmosis is diffusion through a membrane, which generally restricts the movement of dissolved elements more than solvent molecules. Cell membranes allow osmosis to occur, living cells can be considered an osmotic system. Osmosis is largely determined by the chemical potential of water or water potential which describes the ability of water molecules to carry out diffusion. The potential of pure water is expressed as zero (which is a convention), the units of which can be in the form of pressure units (atm., bar) or energy units. The water potential will be negative if the water potential in the system is lower than pure water and will be positive if the water potential in the system is greater than the pure water potential. Water will move from higher potential to lower potential. So diffusion, including osmosis, occurs as a result of a gradient in the free energy of the diffusing particles. The absolute value of water potential is not easy to measure, but the difference can be measured. As a guide or basis, the potential of pure water is taken. So water potential is the difference in free energy or chemical potential per unit molal volume between pure water at atmospheric pressure is zero, and the potential of water in cells and solutions is less than zero or negative. Water potential is a statement of the free energy status of water, a measure of the force that causes water to move within a system, such as plant tissue, soil or atmosphere, or from one part to another in a system. Water potential is perhaps the most useful parameter to measure in relation to soil, plant and atmospheric systems. Osmotic potential is the potential caused by dissolved substances. The sign is always negative. Pressure potential is the potential caused by the hydrostatic pressure of cell contents on the cell wall. The value is always marked with a positive number, zero or can also be negative. Adding pressure (forming turgor pressure) results in a more positive pressure potential. The matrix potential is caused by water binding to the protoplasm colloid and the surface (cell wall). The matrix potential has a negative sign, but in general in vacuolated cells, the value is negligible. Water potential can provide an idea of the water status in a plant or part plant or a system. The water potential of a system is the capacity of an equal number of pure water molecules, at the same atmospheric pressure and temperature. The osmotic potential of the solution is negative because the solvent does less work than pure water. What is meant by work is the movement of pure water into solution. Work is measured in energy units: kJKg-1 or Jmol-1.