Osmosis is defined as the movement of water from its higher chemical potential to its lower chemical potential through semipermeable membrane. The chemical potential of water is also called water potential.
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Osmosis is a special type of diffusion that occurs through a semipermeable membrane.
Osmosis is of two types:- a) Exosmosis b) Endosmosis
a) Exosmosis:- It is the outward movement of water from a cell when it is placed in a solution of higher concentration .
b) Endosmosis:- Osmotic inflow of water into a cell when it is placed in a dilute solution having the solute concentration lesser than that of a cell.
Osmotic pressure:- It is the pressure which develops in a osmotically active solution when it is separated from its pure solvent by a semipermeable membrane. Osmotic pressure is also defined as the pressure required to completely stop the entry of water into an osmotically active solution across a semipermeable membrane. It is measured in atomspheres, bars or pascals. The instrument used to measure osmotic pressure is called osmometer.
Significance of osmosis:- i) Osmosis helps in the absorption of water and minerals by roots.
ii) Cell to cell movement of water occur by osmosis.
iii) Opening and closing of stomata are due to osmotic changes in guard cells.
iv) It provides turgidity to guard cells and therefor plant organ.
v) The plant movement like nyctinasty etc. occur due to changes in osmotic pressure.
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