Question

Guttation is mainly due to
(a)Root pressure
(b)Osmosis
(c)Transpiration
(d)Imbibition

Answer 1

Hint: The exudation of water with the minerals and salt through hydathodes is known as Guttation. Guttation usually occurs at night and early hours of the morning.

Complete answer:
Guttation is mainly due to the ‘Root pressure’. As various mineral ions from the soil are actively transported into the vascular tissue of the roots, water follows and increases the pressure inside the xylem. This positive pressure is termed as root pressure. The effect of root pressure is observable during the early morning and at night, when transpiration is low. It decreases as the day advances. Therefore, root pressure is too weak a force to command for movement of water to the top of tall trees, instead it usually provides a gentle push in the overall process of water transport.

Additional information:
In many herbaceous plants, root pressure has one more effect. When root pressure is high and transpiration is low, herbaceous plants may lose small quantities of excess water in the form of drops from the margins of the tip of leaves. This loss of water in the form of liquid droplets occurs through special openings of veins near the tip of grass blades i.e., hydathodes. A Hydathode comprises a pore in the epidermis accompanied by large intercellular spaces and roughly arranged parenchyma called epithem and blindly ending xylem elements. The process of exudation of liquid drops from the margin of the leaves is called guttation. Such lost water contains several dissolved organic and inorganic substances. This happens due to the development of positive pressure in the xylem present at the vein endings, which forces the liquid to come out through these special openings i.e., hydathodes.

So, the correct answer is ‘Root pressure’.

Note:
Root pressure can only provide a modest push in the overall process of water transport. They do not play a major role in water movement up tall trees. Its major contribution is to re-establish the continuous chains of water molecules present in the xylem which sometimes break under the huge tensions created by the transpiration.