visualizing potato plasmolysis

John Hewitson 100600.70 at
Wed Jan 31 02:51:16 EST 1996

We have done a similar practical for many years, but our solution has been to
use Rhubarb petiole epidermis (some of the cells contain pigment), or more
recently, Onion bulb scales' epidermis (which being 1 cell thick, is easy tissue
in which to observe plasmolysis).

It is possible to estimate Water Potential using Chardakov's Method and Osmotic
Potential by Incipient Plasmolysis.

There are some "tricks of the trade":-  Strip the epidermis and plunge it
straight into sucrose (else it dries very quickly). Immerse the epidermis in
only a small amount of sucrose solution (to get sufficient change in the density
of the sucrose to respond to Chardakov's in only 15 mins).

What puzzled my students and me was that the Pressure Potential which we
calculated from the above gave us a figure of about 10 atmos - which seemed
incredibly high - about the pressure of a lorry tyre!! Can this be true?

It is a good experiment to do anyway - gets students thinking and juggling all
three terms and equations.

Dr. John Hewitson
(Oundle School)
Berrystead Barn
Peterborough, PE8 4DY, UK

e-mail 100600,70 at

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