transpiration 2.3.2

• transpiration is the loss of water vapour by diffusion from the leaves of plants through the stomata when they are opened to allow gas exchange for photosynthesis
• the transpiration stream is the movement of water through a plant from the roots to the leaves as a result of the loss of water by evaporation from the surface of leaves
• 1-water is absorbed in the roots by osmosis into the root hair cell
• 2- water moves from the root hair cell to the xylem by osmosis
• 3- water moves up the xylem driven by the evaporation of water from the surface of the leaves
• 4 - water moves into the leaves from the xylem
• 5- water evaporates from the spongy mesophyll cells water lost from spongy cells is replaced by more water from the xylem
• 6v -air spaces in the leaf become full of water vapour
• 7 - water vapour diffuses through the stomata to the outside air
• higher light intensity and higher CO2 concentration means that more stomata open for photosynthesis to occur, so more water can be evaporated
• higher temperature means that particles have greater kinetic energy so more water evaporates
• dry conditions means a steeper diffusion gradient, so the water vapour diffuses out of leaves faster
• windy conditions removes the evaporated water, maintaining the concentration gradient
• more leaves means there is more surface area for photosynthesis so more CO2 can be absorbed and more water evaporated
• lower light intensity/CO2 concentration means less stomata open which means less water is evaporated
• lower temperature means that particles have less kinetic energy and so less water evaporates
• wet conditions means the concentration gradient is decreased
• less wind means the water vapour is not removed, which reduces the diffusion gradient
• fewer leaves means there is less surface area
• a potometer is used to show the water uptake of a plant under different conditions
• rate of transpiration = distance / time
• the waxy cuticle prevents uncontrolled water loss, as it is waterproof
• stomata are located on the underside of leaves so they are protected from the direct light and energy from the sun
• guard cells close the stomata so no water is lost through them
• wilting is a protection mechanism against future water loss, the leaves collapse and hang down which greatly reduces the surface area available for water loss. stomata close to stop photosynthesis