Investigating transpiration with a potometer


In this investigation students look at the rate of water uptake by a shoot, due to transpiration, using a simple but effective potometer.

There are two main types of potometer used in schools – the mass potometer, which measures transpiration through the loss of mass, and the moving-bubble potometer, which measures water uptake by the shoot.

This design of potometer allows students to combine both measurement techniques, by placing the potometer on a balance, and recording both the change in mass and the volume of water taken up. 

Students set up a potometer and then place it in different situations, changing one environmental factor at a time, such as light intensity, temperature, wind levels etc.

This activity can be done either as a practical by groups of students, or as a demonstration.

For safety reasons, we suggest that a technician sets up the potometers in advance. However, able post-16 students may be able to do some of the setting up themselves, perhaps from step 8 onwards.

You may also wish to show your students our animation on Transport in Xylem and Phloem

Thanks to members of the SAPS Teachers and Technicians Advisory Group for their input into the revision of the original resource, Prof Howard Griffiths of the Dept of Plant Sciences, Cambridge University, and the science club at Didcot Girls School for trialling the activity.

Your FAQs Answered

Q: What plant is best to use?

A: You need a stem that is strong enough to push through the rubber bung and about 4mm in diameter. Often you can find perfect examples in your local area.

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