Water Relation

Water Relation

Introduction:

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:

1) Water is absolutely essential for protoplasm because it's Hydration is essential for its proper organisation and proper functioning of its organelles

 2) Water is the carrier of various dissolved substances like gases, minerals , organic and inorganic substances

3) Water is necessary for metabolic reactions of the cell 

e.g. Photolysis of water

4) The rigidity and turgidity of cells is maintained by and large by water

5) Water forms a continuous network throughout the plant through which dissolved substances move up 

6) Water makes up the loss of water during transpiration and guttation

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.

Osmosis:

The term 'Osmosis' was given by Abbe Nollel .

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) 

• Semi permeable membrane is such type of membrane through which solutes of solution do not pass but solvent passes 

e.g. plasma membrane

Osmotic Pressure or Osmotic Potential:

The applied pressure required to stop osmosis when a solution is separated from pure water by a semi-permeable membrane is called osmotic pressure and usually

The osmotic pressure of a solution is defined as the excess hydrostatic pressure which must be applied to it in order to make its water potential equal to that of pure water

One atm.(S.I. unit of pressure)= 

1.01 bars 

Or one bar = 0.987 atm

Diffusion Pressure Deficit / Water Potential (DPD)WP):

Diffusion pressure deficit is also called suction pressure (S.P) 

It is the ability of a cell to draw water

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

Turgor pressure:

Turgor pressure ia the outward pressure exerted by the cell wall which is developed due to osmotic diffusion of water

Turgor pressure is also called pressure potential

Chemical Potential:

The free energy per mole of a chemical substance is called it's chemical potential

Endo osmosis:

The diffusion of solvent particles into a living cell or structure is called endoosmosis

Exoosmosis: The diffusion of solvent out a living cell or structure is called exoosmosis.

Role of Osmosis:

1) Plants absorb large amount of water from soil

2) Movement and distribution of water across cells is due to osmosis

3) Osmosis is responsible for turgidity of plant cells .The leaf , flower & stem tip require turgor for maintaining their form

4) Turgor of the guard cells is absolutely essential

5) High osmotic conc. increases resistance of the plants to freeezing temperature and dessication

6) It is responsible for turgor pressure in root xylem I e. Root pressure

Imbibition:

• The term imbibition was coined by Sachs . The soaking up of water by dry substances due to hydrophilic colloidsis called imbibition

• It is the first step of the absorption of water 

• The rate of imbibition increases with increase in temperature

• Imbibition pressure is also called Matric Potential

Plasmolysis:

 1) Plasmolysis is the shrinkage of protoplasm due to outward flow of water in a hypertonic solution

2) The point where plasmolysis just starts is called incipient plasmolysis.

Examples:

1)  Raisins swell in water due to imbibition and endosmosis

2) Excess of fertilizer in the soil kills the plant due to plasmolysis

3) Salted pickle or meat kills the bacteria due to plasmolysis

Solution:  is of three types:

A) Hypotonic Solution:

It means weak solution. A cell swells in Hypotonic Solution

B) Hypertonic solution:

Strong solution. A cell shrinks or become flaccid in such solution due to outward flow of water 

C) Isotonic: 

Not weak nor strong solution.A cell remains unchanged in it. Eye drops are always isotonic solution.

Agricos 

Vaishnavi Nimkar 🌾🌱