What is Osmosis?
Movement of water molecules from the region of higher concentration to the region of lower concentration of molecules through semi-permeable membrane until equilibrium is attained is called osmosis.
Explain the mechanism of opening and closing of stomata.
The opening and closing if stomata depends upon turgidity of guard cells.Each guard cell has a thicker wall on the sode facing stoma and a thin wall on the opposite side.Guard cells contain chloroplast.
According to K+ transport Theory, turgidity of guard cell is depending upon the entrance of K+ ions,into the guard cells.ATP helps to intake K+ ions .As the K+ ions enter into the cell, the turgidity of guard cell increases and stomata are opened.
During light malic acid is formed in the guard cells. It dissociates into malate and H+ ions .H+ ions produced in this way are exchanged with K+ ions acid influx of K+ ions takes place in the cell . Potassium malate is formed in the cell and it migrates into the vacuole.This makes the cell osmotically active endosmosis of water takes place into the guard cells.This increases the turgor pressure of guard cells and stomata are open during light, reverse process takes place during night.