Aqa A-Level Biology: Transpiration Study Guide Graded A+

What provides energy to maintain flow of water in plants? {Ans: The Sun provides solar energy > energy is needed for evaporation during transpiration.}Why can you measure water uptake from a plant/leafy shoot for rate of transpiration? {Ans: About 99% of water in plants is used for transpiration.}How does humidity control the rate of evaporation and hence rate of transpiration? {Ans: 1. Humidity of ATMOSPHERE is LOWER than the AIR SPACES next to stomata (inside leaf). 2. Water potential gradient > water vapour diffuses out of open stomata into air. 3. Water lost in this way is replaced by water evaporatinf from cell walls of mesophyll cells into air spaces.}How does TEMPERATURE affect transpiration? {Ans: Increasing temperature increase rate of transpiration - molecules have more KE and rate of evaporation increases.}How can you measure the rate of transpiration with a potometer? {Ans: 1. Leafy shoot with cut stem placed in potometer under WATER - to prevent air entering xylem. 2. All joints are WATERTIGHT; else bubble in capillary tube would move in direction of leak. 3. Air bubble introduced into capillary tube. 4. Rate of water uptake in potometer = rate of transpiration (assuming water