Question

A plant is transpiring rapidly. Will it show root pressure also?

Answer 1

Hint: Water is absorbed by the root system of the plants and the roots are the important organs of absorption. The movement of water upward to reach the leaves requires a pull and pressure system. Root pressure is an osmotic pressure existing within the root cells. This phenomenon takes place in the xylem vessels at the root of a plant. It causes sap or fluids to rise upwards through the stem to the leaves of the plant.

Complete answer:
Root pressure is a transverse osmotic pressure existing in the root system of plants. Osmotic pressure plays a vital role in the biological processes in plants. The osmotic pressure in the peripheral cells of the root is related to supplying sap to the xylem vessels. The conditions that control the movement of water from the soil through the root to the xylem vessels are termed as root pressure.

Root pressure can be observed in the xylem of some vascular plants when the moisture level of the soil is high. It occurs either at night or when the transpiration rate is low during the day. At night it is observed in some plants in which the root pressure causes guttation or exudation of drops of xylem sap. It occurs due to the active distribution of mineral ions into the xylem vessels of the root. Without transpiration, when the ions are carried, they tend to make coagulation in the xylem of the root and the water potential comes down. Then water is absorbed through the process osmosis into the root from the soil. Root pressure is caused due to this coagulation of water and ions in the xylem. It applies to the required force to push the water up to the stem.

Root pressure can be noticed when the shoot of a plant is cut near the soil level and it causes the xylem sap to drop from the cut portion for several hours or days which is due to root pressure.

Root pressure can be noticed only when the transpiration is low or zero. When there is no transpiration root pressure helps to supply the sap but if the plant transpires rapidly then the root pressure won't be generated.

Note: Water is transported through xylem vessels. Under some conditions such as low transpiration, the xylem sap gets more dilute than the soil solution which creates the root pressure. But if the transpiration in a plant goes rapidly then the water and ions solute will be taken up the stems and, in such case, there will be no root pressure. Hence. It can be said that if a plant transpires rapidly it will not show the root pressure.