Question

What is root pressure? How is it useful to plants?

Answer 1

Hint: Root pressure is the force that drives the fluid into the conducting vessels (xylem) of plants from the soil against the gravity. Along with the root pressure transpirational pull also plays an important role in the upward movement of water.

Complete answer: The plant absorbs water from the soil and moves it into the vascular tissue through the apoplast and symplast pathway. Water has to move up the stem and leaves against gravity. The positive pressure in the root which is responsible for pushing up water is known as the root pressure. The root pressure and the transpiration pull plays an important role in an upward movement of water. The pressure present inside the xylem channel of roots i.e. root pressure is also referred to as positive hydrostatic 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 to account for the movement of water to tall trees, it provides a gentle push in the overall process of water transport. In small bushes and plants, root pressure is enough for transport. When the 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 and tips of leaves.

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 greatest contribution may be to restabilize the continuous chains of water molecules in xylem which often breaks under the enormous tension created by transpiration pull.
- Root pressure does not account for the majority of water transport as most plants meet their demand by transpiration pull.