transpiration

• transpiration is the loss of water from the plant by evaporation from the leaves
• this evaperation causes a slight shortage of water in the leaf, so more water is drawn up through the xylem vessel to replace it
• this means more water is drawn up from the roots and there is a constant transpiration stream of water through the plant
• transpiration is a side-effect of the way leaves are adapted for photosynthesis as there is more water inside the plant than outside in the air, the water escapes from the leaves from the stomata via diffusion
• the rate of transpiration depends on factors such as temperature, light intensity, humidity and wind speed
• increasing temperature increases the rate of transpiration because warmer air can hold more moisture - this creates a greater concentration gradient between the inside and outside of the leaf which drives faster diffusion outwards
• light intensity affects the rate of transpiration because when plants are exposed to bright sunlight they open their stomata wider to allow more CO2 into the leaf for photosynthesis but this also allows more water vapour to escape
• light intensity affects the rate of transpiration because when plants are exposed to bright sunlight they open their stomata wider to allow more CO2 into the leaf for photosynthesis but this also allows more water vapour to escape
• humidity affects the rate of transpiration because if the air around the leaf is already saturated with water then less will be lost by diffusion across the surface of the leaf
• increasing temperature increases the rate of transpiration because warmer air can hold more moisture which makes the difference between the concentration of water vapor inside and outside the leaf greater
• light intensity affects the rate of transpiration because when plants are exposed to bright sunlight they open their stomata wider to allow more carbon dioxide into the leaf for photosynthesis but this also allows more water out of the leaf