Investigating osmosis: measuring the water potential of a potato cell

Understanding the osmotic potential of plant cells is a key part of understanding cellular processes. Here we present two methods of determining osmotic potential of plant tissues using potatoes.

Method one, the standard protocol for measuring weight change of tissues in varying osmotic solutions, is reliable but does not demonstrate the changing solute potentials.

The second method, the Chardakov method, is slightly more challenging, but far more visual. Here students can observer changing solute potentials, by observing the resulting density change in sugar solutions in which potato tissue has been immersed. A coloured extract of the bathing solution can be seen to fall, rise or disperse when added to a known molar sugar solution.

This could be attempted as an individual investigation, or could be presented to the class as a demonstration with flex/webcams on the whiteboard.