Water Potential, Solute potential, Pressure Potential - needed in trasportation in plant

 

• The parts of plants that are found under the soil are referred to as  root system.

• The root system includes root and their root hair. Plants absorb water from soil through the root system.

• Plant cells  have a covering followed by the cell wall. This covering is selectively permeable and allows the solvent without any obstacle. This covering is called plasma membrane. 

• The term protoplast is collectively used for the plasma membrane and protoplasm. The protoplasm of one cell is connected to the other cell by plasmodesmata.

• The water is the most essential solvent that passes through the plasma membrane  for the conduction of vital functioning of the plants.

• The small portion of water is retained in plant cells whereas most portions are passed from the aerial part of the plant  by a process of transpiration. To summarised the plants relation with water,some term are essential. These terms are as follows- 

Water potential [ψw]

• The energy of water by which water has the property of buoyancy  is termed as water potential.

• Due to water potential, water moves from one cell to another cell  or from one part of the plant to other parts of plants.

• Water always flows from a region of higher water potential to the region of lower water potential.

• Osmotic movement of water involves the particular work done.

• The major driving factor behind this movement is the difference between the water potential.

• The water potential  is determined by the symbol [ψw] and  Water potential is measured by the Pascal [Pa].

👌👌Remember -The water potential of pure water is zero at atmospheric pressure therefore  all the solutions at atmospheric pressure have lower water potential than water. All the solutions have a negative value of water potential or if we add solute in fresh water then water potential of water is decreased.

• Since the water potential of pure water is zero but its value is positive. As solute is added its value goes into negative value.

• Hence, the movement of water occurs from a region of higher water potential or positive water potential   to a region of lower water potential or Negative water potential.  

• Water potential of any solution is determined by the solute dissolved in solution. [ψs], Pressure potential [ψp] and Gravity [ψg]. This can be represented by the equation-

ψw = ψw + ψp + ψg

• In case of plant cell, only [ψs] and [ψp] are essential and represented by the equation-

 ψw = ψp + ψp

Solute potential [ψs] & Pressure potential [ψp]

• Both these are components of water potential. The solute potential determines the water potential.

• The potential that  exists due to the presence of solute molecules is termed solution potential. It always has a negative value.

• As solutes dissolve in water, the  water potential is decreased. When the concentration of solute increases in the cell, the solute potential  is decreased. As a result, water potential is also decreased.

• When water  is moved into the cell from outside then water exerts pressure on the wall of cells. As a result the cell becomes turgid.

• This turgidity of the cell is due to the pressure potential. Term hydrostatic pressure is also used for the pressure potential. Pressure potential increases the water potential.

• Water due to its  water potential, can move  from outside to inside the cell. The water can move out of the cell if an external pressure is applied on the cell.

• The external pressure increases the water potential of the cell and  the water will expel out.

• The two basic factors that affect the water potential are the amount of solute and external pressure.