Ans.On the basis of the available amount of water and salts, plants are divided into three
groups Figure 11.1
.
Hydrophytes are the plants which live completely or partially submerged in freshwater. Such plants do not face the problem of water shortage.
Osmotic Adjustment
They have developed mechanisms for the removal of extra water from their cells. Hydrophytes have broad leaves with a large number of stomata on their upper surfaces. This characteristic helps them to remove the extra amount of water.
Example
The most common example of such plants is water lily.
Xerophytes live in dry environments.
Osmotic Adjustment
i) They possess thick, waxy cuticle over their epidermis to reduce water loss from internal tissues.
ii) They have less number of stomata to reduce the rate of transpiration.
iii) They have deep roots to absort maximum water from soil.
iv) Some xerophytes have special parenchyma cells in stems or roots in which they store large quantities of water. This makes their stems or roots wet and juicy
Examples. • ,
Cacti (Singular: Cactus) are the common examples of such plants.
Halophytes live in sea waters and are adapted to salty environments.
Osmotic Adjustment
Salts enter in the bodies of such plants due to their higher concentration in sea water. On the other hand, water tends to move out of their cells into hypertonic sea water. When salts enter into cells, plants carry out active transport to move and hold large amount of salts in vacuoles. Salts are not allowed move out .through the semi-permeable membranes of vacuoles. So the sap of remains even more hypertonic than sea water.in this way, water does not move out of cells.
Examples
Many sea grasses are included in this group of plants