Q.3 Describe osmotic adjustments in plants. OR On the basis of the available amount of water and salts,
plants can be divided in how many groups? Explain.
Answer:
On the basis of the available amount of water and salts, plants are divided into three groups.
1. Hydrophytes 2. Xerophytes 3. Halophytes
1. Hydrophytes
Definition
Hydrophytes are the plants which live completely or partially submerged in freshwater. Such plants do not face the problem of water shortage.
Adaptations
They have developed mechanisms for the removal of extra water from their cells.
Large number of Stomata
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.
Examples
The most common example of such plants is water lilly.
2. Xerophytes
Definition
These plants live in dry environments.
Adaptations
i. Cuticle
They possess thick, waxy cuticle over their epidermis to reduce water loss from internal tissues.
ii. Less Stomata
They have less number of stomata to reduce the rate of transpiration.
iii. Deep roots
Such plants have deep roots to absorb maximum water from soil.
iv. Special Parenchyma cells
Some xerophytes have special parenchyma cells in stem or roots in which they store large quantities of water. This makes their stems or roots wet and juicy, called succulent organs.
Examples
Cacti (singular cactus) are common
examples.
3. Halophytes
Definition
These plants live in sea water and are adapted to salty environments. 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 the hypertonic sea water.
Adaptations Holding of large amount of Salts
When salts enter into cells, plants carry out active transport to move and hold large amount of salts in vacuoles. Salts are not allowed to move out through the semi-permeable membranes of vacuoles. So the sap of vacuoles 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 plant.