Investigate the Water Potential of Potato Cells
In my investigation, I hope to determine the water potential of potato
cells. The plant material I will use in my investigation will be
potato chips, which I will cut myself prior to the investigation.
I hope to find the concentration of a solution where the chip stays
the same mass and length, which will tell me that the water potential
inside the cells is the same as the water potential outside the cells.
Osmosis is defined as the movement of water through a semi-permeable
membrane. Semi - permeable membranes are permeable to water but
impermeable to certain dissolved substances. In the case of this
experiment, the sucrose molecules cannot diffuse through the cell
membrane because the sucrose molecules are much bigger than water
The water potential of a solution is a measure how dilute the solution
is, and therefore of how readily water will diffuse from this
solution, through a semi-permeable membrane, into another solution.
Pure distilled water has a water potential of zero: the water
potential becomes more negative as more substances are dissolved in
it. When two solutions are separated by a semi-permeable membrane,
water moves from the side with high water potential to the side with
low water potential:
If we dissolve substances in water we lower the water potential of the
High water potential Some water potential Low Water Potential
Chip grows Chip stays the same Chip shrinks
o Mass of the chip - I think that the larger the mass of the chip then
the bigger the difference in results will be, therefore I think that
to make experiment more easy it would be best to use a large chip.
o Dimensions (length, cross-sectional area) - I believe that changing
the dimensions of the chip would have a similar effect to changing the
mass of the chip. I will measure the length and cross-sectional area
for each chip.
o Time the chip is left in the solution - I think that if I were to
leave the chips in the solution for only a small amount of time there
might not be sufficient time for the osmosis to occur, so that the
chips would not differ in size enough for conclusive results.
Therefore, I will need to give a good amount of time for the osmosis
o Temperature - I believe that all reactions happen quicker when there
is a higher temperature, so diffusion across the membrane may be
faster at higher temperature.
o Concentration of sucrose solution - I think that the lower the
concentration of the external sucrose solution, the more the chip will
expand (because the cells become turgid).
o Total Volume of sucrose solution - I think that changing the volume
of sucrose solution may affect the results of my investigation.
Variable I will change:-
I will change the concentration of sucrose solution in my experiment,
because I believe...