A potometer is a piece of apparatus designed to measure water uptake in a leafy shoot.
There are 2 types of potometer – the bubble potometer and the weight potometer.
As water is transpired from the leaves, the shoot absorbs water from the potometer.
The distance the air bubble moves in a certain period of time can be used to calculate the rate of water uptake.
The apparatus and plant is weighed and then left for a period of time.
When reweighed the amount of water lost by the plant can be calculated.
A top pan balance that measures to two decimal points provides great accuracy.
A potometer can measure the amount of water taken up by a leafy shoot but cannot provide an accurate value for the amount of water transpired, because some water will be used in photosynthesis and to provide turgor.