Transpiration Flashcards
Transpiration
Evaporation of water from leaves
Effect of Temperature
Increasing temperature increases rate of transpiration as water molecules have more kinetic energy and so evaporate more quickly
Effect of Wind/Air Movement
Increasing air movement increases the rate of transpiration as the wind moves moist air away from the leaf. This increases the water potential gradient so water is lost more quickly.
Effect of Humidity
Increasing humidity decreases the rate of transpiration. This is because the moist air outside the leaf increases the water potential but decreases the water potential gradient. Water is therefore lost less quickly.
Effect of Light Intensity
Increasing light intensity increases transpiration rate. This is be a cute there is more photosynthesis which means the stomata need to be open to facilitate gaseous exchange. This means water is lost more quickly by transpiration.
Calculate rate of transpiration using potometer
- need to measure the distance the bubble moved and time taken
- need the radius of the tube (so can calculate the volume) to measure in cm^3/mm^3 per min
Precautions of photometer and why (9)
- seal joints/ ensure airtight/ ensure watertight so no air bubbles
- cut shoot at a slant to increase surface area
- cut shoot under water
- dry off leaves to increase water potential gradient
- insert into apparatus under water
- ensure no air bubbles are present
- shut tap
- note where bubble is at start/ move air bubble to start so can calculate the rate
- reset bubble to start using reservoir (control)
Potometer actually measures …
Potometers actually measure the rate at which water is up-taken rather than the rate of transpiration. This is because somer water is used during photosynthesis and some water is lost/ gained in hydrolysis/ condensation reactions.
