How do you work out the rate of uptake from a potometer?
Reveal answer
Distance bubble moves ÷ time (× tube area for volume).
Key words: distance · time
3(h) TRANSPORT · RECALL
3.8B Environmental factors and transpiration
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In a potometer experiment, why is a heat shield used with the lamp?
Reveal answer
To keep temperature constant while light intensity changes.
Key words: temperature
Why let the shoot adjust after changing conditions?
Reveal answer
Rate needs time to change → wait until steady → valid reading.
Key words: steady
What is meant by the term potometer?
Reveal answer
Apparatus measuring water uptake by a cut shoot.
Key words: potometer
What is meant by the term proxy?
Reveal answer
Indirect measure used to estimate another quantity.
Key words: proxy
What is meant by the term capillary tube?
Reveal answer
Very narrow tube in which small volume changes are visible.
Key words: capillary tube
What is meant by the term acclimation?
Reveal answer
Time allowed for a plant to adjust to new conditions before measurement.
Key words: acclimation
Variables in a wind-speed investigation, Independent. Example? How managed?
Reveal answer
Example: Fan speed or distance. How managed: Set measured levels.
Key words: Independent
Variables in a wind-speed investigation, Dependent. Example? How managed?
Reveal answer
Example: Bubble distance per minute. How managed: Use the same capillary scale and timer.
Key words: Dependent
Variables in a wind-speed investigation, Control variable (Leaf area). How managed?
Reveal answer
Use the same shoot throughout or normalise by area.
Key words: Control variable
Variables in a wind-speed investigation, Control variable (Temperature/light/humidity). How managed?
Reveal answer
Monitor and keep constant.
Key words: Control variable
Variables in a wind-speed investigation, Reliability. Example? How managed?
Reveal answer
Example: Repeated readings. How managed: Reset bubble and calculate a mean.
Key words: Reliability
True or false, and why? “A potometer directly measures transpiration.”
Reveal answer
False. It measures water uptake; this is an approximation to water loss.
True or false, and why? “A faster bubble means air is entering the plant.”
Reveal answer
False. The bubble marks water displacement in the capillary.
True or false, and why? “Moving a lamp changes only light intensity.”
Reveal answer
False. It may change leaf temperature too, so temperature must be monitored or controlled.