Transpiration

• Water is drawn into the roots of plants from the soil. Water moves into the root hairs by osmosis. Mineral ions move from the soil into the root hairs by active transport
• Water flows from the roots through xylem in its stems to its leaves. Xylem tissue is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream from the roots to the leaves.
• Water evaporates in the leaves and the water vapour escapes through tiny holes in the surface of leaves called stomata. The stomata can open or close as conditions change because the guard cells can gain or lose water by osmosis.
• The rate of transpiration varies with: • light intensity, which affects the opening of stomata • air movements, which affect the concentration of water vapour in the air around leaves • temperature, which affects the rate at which water evaporates