CBSE Class 10 Answered

Mechanism of Transport of Water and Minerals

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.

Mechanism of Transport of Food

Food synthesised during photosynthesis is loaded into sieve tubes by utilising ATP. The presence of food inside the phloem develops the concentration gradient of water. Thus, water enters the phloem by osmosis. Osmosis develops high pressure inside the phloem which transports the food from the phloem to plant parts where the concentration of food is less. This process is called translocation. In spring, the sugar stored in the root or stem tissues is transported to the buds.