1. The discovery of enzyme phosphorylase in guard cells by Hanes (1940) greatly supports the starch-sugar interconversion theory.
2. The enzyme phosphorylase hydrolyses starch into sugar and high pH followed by endosmosis and the opening of stomata during light. The vice versa takes place during the night.

High concentration of salt in the soil leads to high osmotic potential, which may a result in wilting of plants due to following reasons.
(a) This may be due to osmotic withdrawal of water from a cell or system when it is placed in a hypertonic solution called Exosmosis.
(b) Exosmosis in a plant cell leads to plasmolysis. As a result of water loss in the cell protoplasm shrinks and the cell membrane is pulled away from the cell wall and finally the cell becomes flaccid.

Water molecules have the strong mutual force of attraction called cohesive force due to which they cannot be easily separated from one another. Further the attraction between a water molecule and the wall of the xylem element is called adhesion.

Aquaporin is a water channel protein embedded in the plasma membrane. It regulates the massive amount of water transport across the membrane. Plants contain a variety of aquaporins.

The net movement of molecules from a region of their higher concentration to a region of their lower concentration along a concentration gradient until an equilibrium is attained.

1. Apoplast
2. Symplast
3. Transmembrane route

Uses:
1. Antitranspirants reduce the enormous loss of water by transpiration in crop plants.
2. Useful for seedling transplantations in nurseries

1. The phenomenon of food transportation from the site of synthesis to the site of utilization is known as translocation of organic solutes.
2. The term solute denotes food material that moves in a solution

Deplasmolysis
1. The effect of plasmolysis can be reversed, by transferring the plasmolysed cell into water or hypotonic solution. Due to endosmosis, the cell becomes turgid again.
2. It regains its original shape and size. This phenomenon of the revival of the plasmolysed cell is called deplasmolysis. Ex: Immersion of dry raisin in water.

1. When a plant cell is kept in a hypertonic solution, water leaves the cell due to exosmosis.
2. As a result of water loss, protoplasm shrinks and the cell membrane is pulled away from the cell wall and finally, the cell becomes flaccid. This process is named as plasmolysis

Significance of imbibition:
1. During germination of seeds, imbibition increases the volume of seed enormously and leads to bursting of the seed coat.
2. It helps in the absorption of water by roots at the initial level.

1. In facilitated diffusion, molecules cross the cell membrane with the help of special membrane proteins called transport proteins, without the expenditure of ATP.
2. It is a kind of passive transport occurnng between cells

Channel protein and Carrier protein are two types of transport proteins present in cell membrane.