Biological termModerate0.5 marks
6(b)
Give appropriate biological / technical terms for the following:
An apparatus that measures the rate of water uptake in a cut shoot due to transpiration.
Topic: Potometer
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Answer
Exam answer
POTOMETER (Ganong’s potometer).
Explanation
A potometer measures the rate at which a cut shoot TAKES UP water, and that is used as a measure of the rate of TRANSPIRATION.
NOTE THE LIMITATION, which is itself an examination question: the two are NOT identical. Not all the water absorbed is transpired — some is used in photosynthesis and retained in the tissues — so the reading is only an approximation.
A second limitation: it is difficult to keep the apparatus airtight and to insert the shoot without an air bubble entering the xylem, which would block the water column altogether.
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