Investigating Osmosis in Potato Cells
To investigate the effect of different concentrations of sucrose
solution, on potato cells
Osmosis is the passage of high water concentration through a
semi-permeable membrane to a region of low water concentration
the passage of water.
Explanation of osmosis
For osmosis to occur there must be;
semi-permeable membranes are very thin layers of material (cell
membranes are semi-permeable) which allow some things to pass through
them but prevent other things
from passing through. Cell membranes
will allow small molecules like Oxygen, water, Carbon Dioxide, etc. to
pass through. Cell membranes will not allow larger molecules like
Sucrose, etc. to pass through.
Regions of high concentrated water are either a very dilute solution
of something like sucrose or pure water. In each case there is a lot
of water, there is a high concentration of water.
Regions of low concentrated water are a concentrated solution of
something like sucrose. In this case there is much less water.
If the solution surrounding the cell has a higher water concentration
than the cell, the cell will gain water by osmosis. Water molecules
are free to pass across the cell membrane in both directions, but more
water will come into the cell than will leave. The cell is likely to
swell up and become 'turgid'.
If the solution is exactly the same water concentration as the cell
there will be no movement of water across the cell membrane. Water
crosses the cell membrane in both directions, but the amount going in
is the same as the amount going out. The cell will stay the same size.
If the solution has a lower concentration of water than the cell the
cell will lose water by osmosis. Again, water crosses the cell
membrane in both directions, but this time more water leaves the cell
than enters it. Therefore the cell will shrink and become 'flaccid'
Potato plant cells:-
Plant cells always have a strong cell wall covering them. When they
accumulate water they swell, but the cell wall prevents them from
bursting. Plant cells become 'turgid' when they are put in dilute
solutions, turgid means to be swollen and hard. The pressure inside
the cell rises and eventually no-more water can enter the cell, this
pressure works against osmosis to become turgid, being turgid is
important because this is what makes the plant stand into the sunlight
to produce more photosynthesis.
[IMAGE] When plant cells are in a concentrated sugar solution they
lose water-using osmosis, they become the opposite of turgid,
'flaccid' the contents of the potato cells
shrinks and come away from
the cell wall.
Diagram of osmosis;
I predict that the higher the concentration the solution is the most
osmosis will occur here as more water will move out of the potato to
balance, meaning that the potato piece will shrink, I think that the
middle solution with the potato will do nothing as there is equal
amounts of both sucrose and water, and I feel that the lower the
sucrose solution will make the potato piece swell, become 'turgid' in
order to balance.
The only variables in this experiment are going to be the
concentrations to test the osmosis activity, everything else should be
kept the same, i.e. the sizes and weights of the potato parts.
The precautions that have to be considered is the fairness of the test
i.e. making sure all the sizes are all the same if not this could be
dangerous, to make sure my hands are dry, clean, if the substances
that may be on my hands could get onto the potato pieces and change
the results and effect the way the osmosis occurs.
The apparatus used were:
Â· Apple Corer - to cut the pieces of potato
Â· Potatoes - may need 2, need them to show the process of osmosis
Â· 6 test tubes - to put the pieces of potato and solution in
Â· Sucrose & water solutions - to put potatoes in, need 7 different
Â· Test tube holders - to hold the test tubes whilst the process takes
Â· Pen, ruler and paper or a book - to record results
Â· Weighing scales - to weigh the potato pieces, could use electronic
ones for a more accurate reading.
An assortment of concentrated sucrose and water solutions, in selected
Sucrose => 30ml | 25ml | 20ml | 15ml | 10ml | 5ml | 0ml
Water => 0ml | 5ml | 10ml | 15ml | 20ml | 25ml | 30ml
A B C D E F G
* Prepare these solutions out in seven different test tubes making
sure that they are all in order i.e. A, B, C, D, E, F, G, and they
all are the same volume. These seven solutions were chosen to show
more of an example how much osmosis occurs between different
* Do this using a measuring cylinder for more accuracy.
* Get 2-3 reasonably sized potatoes, and an apple corer.
* Cut out seven pieces of potato using the apple corer and place
them in a horizontal line.
* Cut each potato piece, so they are all the same length, around
* Make sure the potato pieces are in the same order as the solutions
which are going to be used, i.e. potato piece one goes with
solution A etcâ€¦
* One by one weigh each piece, still keeping sure that they don't
get mixed up, this process can be done using Weighing scales, or
for better accuracy in weight electronic scales can be used.
* Draw a table to record the results.
The table could look like this:-
Sucrose solution Sucrose/Water
Weight Before (g)
Weight After (g)
Change in mass(g)
Size change (cm)
Â· Once all the measurements and weights have been taken on each potato
piece. Then take a recording of the time and place all seven pieces of
potato in its corresponding test-tube.
Â· Now, leave the Osmosis to take place for around 15-20 minutes, we
leave the experiment for 15-20 minutes because, 1. It gives more
chance for osmosis to happen, 2.Better and more accurate results can
Â· To gain an average do this test a couple of times.
The experiment was kept fair by ensuring that all Potato pieces got
the same time in the solutions, i.e. approx 20 minutes, they were then
cleaned using a paper towel so that any sucrose solution would change
or interfere with the weight results. Each time the experiment was
done the things that were kept the same were;-
i. Volume of solution used in each test (30ml)
ii. Time during the experiment (20 minutes)
iii. Sizes of each potato piece (Length & Width)
Safety was not so as important in this experiment as it would be with
other i.e. using acid etc. as we were only using a sucrose solution
"sugar solution", the only danger factor with this was that if it was
spilt it is quite a slippery substance, so it would need to be cleaned
Accuracy and Rangeof Readings:
To make this experiment as accurate as possible we needed to make sure
that the lengths of the potato pieces and the solutions were the same
volume every time, so we checked that the volumes were 30ml, and sizes
were around 2cm, Also we tried to keep the pieces in the solutions for
at least 20 mins to get a good reading. Two sets of results will be
obtained for an average to be calculated.
Sucrose solution Sucrose/Water
Size Before (cm)
Size After (cm)
Weight Before (g)
Weight After (g)
From my investigation I have found out that using my results and in
the graphs that were made from the results, the graph for Average
length change overall there is an increase in length but when looking
further into the size for the before and after graph, I noticed that
there are some anomalies within this such as in concentration numbers
2 and 5 as the decreased in size which was not expected, the perfect
results for this graph would be for the line for the size after to
have an increase whilst going down in concentration, overall the
average length graph is quite accurate, the start, middle and end
results turned out as expected which was good.
To improve on this, the anomalous points could be done again to see if
the results still turned out the way they did before, or different, I
would think they would come out different when looking over my
hypothesis and research.
The results and graph produced for the change in weight were not as
expected when the experiment in this experiment, I got some strange
results ones which were not very accurate, the only accurate ones were
the middle (concentration #G) as it was researched and predicted to
turn out that way. I feel that the lowest concentration was not right,
or it did not agree with my prediction as I thought that as it would
become turgid it would get heavier, this could be done again to see if
it is right, in this weight graph there are a couple of anomalous
points such as concentration #C, it should not have lost so much
weight according to my research (see preliminary work). As I said
previously to improve on this I think that the test could be done
again for the weight to see if the results occur to be the same
I feel that the overall procedure went according to plan, using the
method made in the preliminary work, which we further used in the
experiment worked well, we got all the main points needed to do the
experiment and most of the results agreed with my hypothesis. If a
trend line were to be added to the average size change graph it would
be a straight diagonal line which is what should happen. Out of the
graphs produced the length one was the most accurate with it showing
with it showing that the potato does get smaller and become flaccid,
and the opposite way round, i.e. becoming turgid in different
concentrations. This was a good experiment to do, most results were
accurate and it showed in presenting them. The reason some of my
results were not anomalous was because that as osmosis occurs, water
and sugar cross the cell membrane to level out, so the ones with no
sucrose solution present became more turgid because there were no
sucrose to replace some of the water, more water moved into the
To carry this experiment on further, the tests could be done more
times to see if the results are the same, leave the potato pieces in
for a longer period of time too see if this get better results,
possibly use a higher concentration of sucrose or use larger potato