CBSE Class 9 Answered

Water moves upwards from the roots to the different plant parts mainly by two processes-

• Root pressure
• Transpirational pull

Root Pressure

• Water enters the root hair through osmosis, and mineral ions enter the root cells by active transport.
• Both water and minerals move upward from cell to cell through the cortex of the root by osmosis.
• From the cortex, water and minerals are brought to the xylem.
• The sap which contains water and dissolved minerals move upwards from the root cells through the xylem. The upward movement of sap is called the ascent of sap.
• The xylem vessels of the roots are in continuation with the xylem vessels of the stem.

Transpiration Pull

• Transpiration is the loss of water in the form of water vapour from the aerial parts of a plant.
• It occurs through openings called stomata.
• Water loss through evaporation lowers the concentration of water inside the mesophyll cells.
• Due to this, water enters mesophyll cells from neighbouring xylem vessels through osmosis.
• As water evaporates from the leaves, a suction force is created. This force helps to draw more water up through the stem which causes the roots to absorb more water from the soil.
• Higher the rate of transpiration, greater the rate of absorption of water and solutes from the soil.
• Transpiration also helps in maintaining the temperature of the plant body.