N0. 06 The effect on potato tissue of the sugar
concentration of the surrounding liquid
Introduction
Plant cell walls are freely permeable to water and dissolved substances, but the cell
membrane is only partially permeable. Small molecules like water can pass through
freely but larger molecules like dissolved sugars cannot.
By putting potato tissue into solution of different concentrations, it is possible to
change the amounts of water inside the vacuoles of the cells. If the water leaves the
cell, this should reduce the mass of the tissue. If water enters the cell, the mass of the
tissue will increase. The potato tissue can be weighed and its length measured before
and after the experiment to see how much water has been lost or gained in each
solution.
Planned Procedure
Fifteen tubes are labelled : 3-- distilled water, 3--10% Sucrose, 3--20% Sucrose
3--30% Sucrose
3--40% Sucrose
( 3 of each are used to obtain a more
accurate average result)
Next 20-30ml of distilled water or correct concentration of sucrose is put into the
tubes. To make the test fair place the same amount of liquid in each tube. The liquid
should be high enough to allow for expansion of the tissue with out it becoming
uncovered.
A cork borers will be pushed into a potato using a cutting tile to cut onto. Then push
the potato tissue out using smaller borer or mounted needle. Using a ruler+ scalpel
cut 15 piece ( cylinders of potato) accurately into the same length (70mm or as long as
possible) and record.
Measure the mass of each piece using scales provided, then place in boiling tube,
record weight on the label.
Leave for 24 hours. All tubes in the same conditions to ensure the test is fair.
The only varied factor is the solution sugar concentrations
Mean while make a chart to record original weight, final weight and change in weight
of each sample. 3 samples at each of the five concentrations. Do the same for
length.
After 24 hours weigh and measure the length of each piece. Recording its original
weight, final weight and length in the chart. ( Before weighing dry each piece with a
paper towel.)
Calculate the mean (average) change at each concentration. Then plot two graphs.
One the different concentration of the surrounding fluid. Against the change in mass
The other different concentration of the surrounding fluid against the change in
length.