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Potometer and Rates affecting Transpiration
Transcript of Potometer and Rates affecting Transpiration
Write out all the factors affecting the rate of transpiration, from page 13, and write the correct explanation next to it.
Explain why water loss from the leaves of a plant is unavoidable?
Give three benefits of transpiration to plants.
Describe the cohesion-tension theory.
What is the term used to describe the attraction of water to the surface of the xylem vessels?
How could you compare the results from two separate experiments?
Set up in same
per unit area of leaf
Run for the same
length of time
the plants at the same time, etc
TRANSPORT IN PLANTS
Potometer and factors affecting the rate of transpiration
To describe how to measure transpiration using a potometer, and to explain what factors affect the rate of transpiration.
Do the past paper questions.
Measuring transpiration in a lab
is used to measure transpiration
BUT really measures uptake of
by the plant.
It is assumed that water uptake is directly related to water loss from the leaves as 99% of water taken up is lost in transpiration.
Use these words to fill in the blanks.
Air / Water
cut shoot water
Factors affecting the rate of transpiration
These can either be to do with the plant or its environment.
Anything that increase the water vapour potential gradient between the inside and outside of the leaf will increase water loss.
Match the factors with its explanation, on
Use numbers to match.
Feature that affects
the rate of water loss.
How it affects water loss.
Number of leaves
More leaves larger surface area over which vapour can be lost
Number size, position
Many large stomata, water vapour lost more quickly. Stomata on lower surface, water vapour loss is slower
Presence of cuticle
Waxy cuticle reduces evaporation from leaf surface
Stomata open to allow gaseous exchange for photosynthesis
Higher temperature will increase rate of water loss:
Increase rate of evaporation from cell surface so water vapour potential in leaf rises
Increase rate of diffusion through stomata as water molecules have more kinetic energy
Decrease relative water vapour potential in the air, allowing more rapid diffusion of molecules out of leaf
Higher relative humidity in air will decrease rate of water loss – smaller water vapour potential gradient between air spaces in leaf and outside.
Air movement or wind
Air moving outside of leaf will carry away water vapour that just diffused out of leaf. This will maintain a high water vapour potential gradient.
If there is little water in the soil, then plant can not replace the water that is lost. Water loss in plants is reduced when stomata are closed or when the plants shed leaves in winter.
insert into apparatus under water
full of water/no extra bubbles/no
cut shoot at a
ensure tight joints
air / water
allow time to
keep condition(s)/named condition(s)
introduce an bubble
measure moved per unit time
shut screw clip
ref. to ; e.g. note where bubble
is at start