Answer:
Explanation:In this article we will discuss about the water relation in plants.
Plant physiology is the study of vital or functional activities of plants. And water is essential for these functional activities.
What for water is needed:
i. Water is absolutely essential for protoplasm because its hydration is essential for its proper organisation and proper functioning of its organelles.
ii. Water is the carrier of various dissolved substances like gases, minerals, organic and inorganic substances etc.
iii. Water is necessary for metabolic reactions of the cell e.g., photolysis of water.
iv. The rigidity and turgidity of cells is maintained by and large by water.
v. Water forms a continuous network throughout the plant through which dissolved substances move up.
vi. Water makes up the loss of water during transpiration and guttation.
Thus almost all the functional activities of plants depend on the water relation.
Under water relation we study the following points:
a) How does water enter into the plant – This functional activity is studied under the heading ‘Osmosis’.
b) How does water move up inside the plant – It is studied under ‘Ascent of sap’ or ‘Translocation of sap’.
c) How is water lost from the plant – It is studied under ‘Loss of water’ or ‘Transpiration’.
Diffusion:
The movement of the molecules of gases, liquids or solutes from the regions of higher concentration to the regions of lower conc., until the molecules are evenly distributed throughout the available space is known as Diffusion.
Diffusion Pressure Deficit/Water Potential (DPD/WP):
Diffusion pressure deficit (DPD) is also called suction Pressure (S.P). It is the ability of a cell to draw water. It is the force per unit area (i.e., pressure) by which water enters into a cell. A pure solvent is supposed to have maximum diffusion pressure.
When certain solute particles are added to the pure solvent, the diffusion pressure of the resulting solution is lowered. The amount by which the diffusion pressure of a solution is lowered than that of its solvent at the same temperature and atmospheric pressure, is called DPD. The term DPD was introduced by Meyer in 1938.
But according to the recent trend, diffusion of water is explained in terms of Water Potential. DPD is the positive value whereas water potential is the negative value.
Turgor Pressure (T.P.):
T.P is the outward pressure exerted by the cell solution on the cell wall which is developed due to osmotic diffusion of water. In equilibrium inward pressure is also given by the cell wall on the cell solution in an equal amount, which is called wall pressure or Hydrostatic Pressure.
Turgor Pressure is also called Pressure Potential (PP) which has positive value.
Chemical Potential:
The free energy per mole of a chemical substance is called its chemical potential. Chemical potential of water in a solution is reduced by the addition of solutes.
Osmosis:
i. Osmosis is essentially a special type of diffusion of liquids.
ii. The term ‘Osmosis’ was given by Abbe Nollel.
iii. Osmosis Means:
a) Movement of solvent.
b) From a region of lower concentration of solution.
c) To a region of higher conc. of solution.
d) Through semi-permeable membrane (SPM).
iv. Plasma or cell membrane is a semi-permeable membrane. At higher temperature plasma membrane becomes permeable.
Illustration:
Answer:
Example of osmosis.
Explanation:
Osmosis is the spontaneous net movement or diffusion of solvent molecules through a selectively permeable membrane from a region of high water potential to a region of low water potential, in the direction that tends to equalize the solute concentrations on the two sides.
Diffusion is the net passive movement of molecules or particles from regions of higher to regions of lower concentration.
The answer cannot be diffusion, and thus, is osmosis.
