Osmosis is the movement of solvent molecules from a
dilute solution to a concentrated solution (or from a pure
solvent into its solution) across a semi-permeable membrane.
Imbibition is the phenomenon by which living or dead cells
absorb water by surface attraction.
Example: Wooden Doors get swollen during
the rainy season.
Dry seeds swell up when placed in a can of water.
Diffusion is movement of molecules of liquids and gases
from their region of higher concentration to their region
of lower concentration until it is same throughout the given
space.
Example: When perfume is spilt in one corner
of a room its fragnance spreads all over the room.
Osmotic Pressure is the pressure exerted by the liquid
column that just prevents the entry of solvent particles
into the solution across a perfectly semi-permeable membrane.
Osmotic Potential of a solution is the tendency of water
molecules to diffuse out of it.It is a measure of the difference
in the concentration of the solution with water.
Isotonic Solutions : Two solutions having the same osmotic
pressure(same concentrations) at the same temperature are
said to be isotonic.
Hypertonic Solution : The solution having the higher concentration
of solute molecules (higher osmotic pressure) when compared
to another solution is said to be hypertonic.
Hypotonic Solution : The solution having the lower concentration
of solute molecules (lower osmotic pressure) when compared
to another solution is said to be hypotonic.
Endosmosis : The inward movement of solvent molecules through
the semi permeable membrane by the process of osmosis is
called endosmosis.
Exosmosis : The outward movement of solvent molecules through
the semi permeable membrane by the process of osmosis is
called exosmosis.
Turgidity : A cell charged with water with its wall in
a state of tension is said to be turgid and the condtion
is described as turgidity.
Flaccidity : A cell no longer charged with water is said
to be flaccid and the condition is described as flaccidity.
Turgor Pressure : The outward pressure exerted by the liquid
contents of the cell on the cell wall under fully turgid
condition.
Wall Pressure : The inward pressure exerted by the cell
wall on the liquid contents of the cell under fully turgid
condition.
Suction Pressure : It is a measure of the water absorbing
power of a cell. It is the difference between the Osmotic
Pressure and the Turgor Pressure.
Plasmolysis : The shrinkage of the protoplasmic contents
away form the cell wall when the cell is placed in a hypertonic
solution.
Deplasmolysis : The return of a plasmolysed cell to its
normal condition when placed in a hypotonic solution.
Ascent of Sap : The upward movement of water and dissolved
minerals from the root to the top of tall trees through
the xylem vessels.
Root Pressure : It is the pressure exerted by the cortical
cells of the root upon their fluid contents under fully
turgid condition ; forcing a quantity of them into the xylem
vessels and upwards into the stem.
Capillarity : It is the phenomenon by which liquids rise
to the greatest height in tubes having the narrowest bore(diameter).
Significance Of Osmosis
In Plants :
1.Absorbption of water from the soil.
2.Opening and closing of stomata.
In Animals :
1.Fresh water animals have to maintain their osmotic
pressure with the external environment. Thus they are either
having a contractile vacuole (as in amoeba)
which discharges the waste materials or kidneys
(like in fish and frog).
2.In land animals kidneys regulate the osmotic pressure
of the blood.
Marine fishes being in a hypertonic medium tend to accumulate
salts in their body .Thus when they are placed in tap water
their cells 'burst' due to absorbing excess water.
Differences between Osmosis and Diffusion
Osmosis
1.It involves flow of solvent molecules
in one direction.
2.It requires semi permeable membrane.
3.It is a slow process .
4.Occurs only in liquids.
5.The movement is over a short
distance.
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Diffusion
1.Flow of either solute or solvent molecules
is in both directions.
2.No such membrane is required.
3.It is a fast process.
4.Occurs in liquids as well as gases.
5.Movements are over large distances. |
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