Question

why is air free water used in the potometer

Answer 1

A potometer is a device used for measuring the rate of water uptake of a leafy plant shoot. The main reason for water uptake by a cut shoot is transpiration (evaporation in plants) and is affected by the transpiration stream.

Answer 2

Explanation:

A potometer is also known as a ‘transpirometer’. It is an instrument used to measure the amount of water lost by a leafy shoot which is measured by the water uptake by the plant or shoot. The water is taken up by the shoot or root of the plant and from the surface of the leaf the water is lost by transpiration or used in photosynthesis.  

Air content in the water, i.e., in the ‘presence of oxygen’ in the water, this can get used up by the plant to break down carbohydrates into energy. Therefore it would not give an accurate measurement of the ‘amount of water lost’ by transpiration. Hence it is ‘essential to ensure’ that the water in photometer is air-free.