IGCSE Biology glossary
Potometer
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Definition
A piece of apparatus used to measure the rate of water uptake by a cut shoot, which is used as an estimate of the rate of transpiration. It works by tracking the movement of an air bubble along a graduated capillary tube as the shoot takes up water.
What to include in an exam answer
A potometer measures water uptake, not transpiration directly. Some water taken up is used in photosynthesis or for cell expansion, so water uptake is slightly greater than water lost by transpiration.
Example in context
Explain why a potometer does not measure transpiration precisely (2 marks): A potometer measures water uptake by the shoot, not water loss from the leaves. Some of the water absorbed is used for photosynthesis or to maintain turgor, so water uptake is slightly greater than transpiration.
Related syllabus topic
Transport in plants