the rate of transpiration & measuring transpiration Flashcards
name four things which affect the transpiration rate
light intensity
temperature
air flow
humidity
how does light intensity affect the rate of transpiration?
increasing the light intensity increases the rate
how does wind speed affect the rate of transpiration?
increasing wind speed/air flow increases the rate
how does temperature affect the rate of transpiration?
increasing the temperature increases the rate
how does humidity affect the rate of transpiration?
increasing humidity decreases the rate
why does temperature affect the rate of transpiration?
when it is warmer, the water particles have more energy to evaporate and diffuse out of the stomata
what happens if the air flow is poor around a leaf?
The water vapour just surrounds the leaf and doesn’t move away. This means there’s a high concentration of water particles outside the leaf, as well as inside it so diffusion doesn’t happen as quickly.
what happens if the air flow is good around a leaf?
The water vapour is swept away maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of high concentration to an area of lower concentration.
why does diffusion happen slower if the air is humid around a leaf?
Diffusion happens fastest if there’s a really high concentration in one place, and really low concentration in another. There is a lot of water in the air already so there isn’t much of a difference between the inside and outside of the leaf, decreasing the concentration gradient meaning diffusion happens slower as there isn’t a huge difference.
why does the transpiration rate decrease at night?
Stomata begin to close as it gets darker, to reduce water loss. Photosynthesis can’t happen in the dark, so the stomata close as they don’t need to be open to let carbon dioxide in. When the stomata are closed, very little water can escape, therefore it reduces transpiration.
how can you use a potometer to estimate transpiration rate?
Set up the potometer and record the starting position of the air bubble. Start a stopwatch and record the distance moved by the bubble per unit time. The further the bubble moves, the greater the transpiration rate as water uptake is directly related to water loss.
why does a higher light intensity increase the rate?
rate of photosynthesis increases so more stomata open allowing the rate of evaporation to increase
