How Osmosis affects Potato chips in Different Concentrations
Length: 2689 words (7.7 double-spaced pages)
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Background: Osmosis is the movement of water molecules across a
partially permeable membrane from a region high water concentration to
low water concentration. A partially permeable membrane is a membrane
with tiny holes in so small that only water molecules can pass
When you place a potato chip in a salt or sugar solution, then if the
potato has higher water potential some of the water will diffuse into
the Sal solution which will cause the chip to lose weight. However the
water amount is in the salt solution is larger then the water will be
diffused to the potato chip thus causing the chip to gain weight. If
the water amount is equal then the weight of the chip will not change.
In a high concentration of water the amount of solute (e.g. sugar) is
low. This could be called a weak or dilute solution. In a low
concentration of water the amount of solute (e.g. sucrose) is high.
This could be called a strong or concentrated solution. When two such
solutions are divided by a semi-permeable membrane the water will move
from the area of high concentration to the area of low concentration,
until both sides have reached equilibrium.
Plant cells always have a strong cell wall surrounding them. When they
take up water by osmosis they start to swell, but the cell wall
prevents them from bursting. Plant cells become "turgid" when they are
put in dilute solutions. Turgid means swollen and hard. The pressure
inside the cell rises and eventually the internal pressure of the cell
is so high that no more water can enter the cell. This liquid or
hydrostatic pressure works against osmosis. Turgidity is very
important to plants because this is what make the green parts of the
plant "stand up" into the sunlight. When plant cells are placed in
concentrated sugar solutions they lose water by osmosis and they
become "flaccid." This is the exact opposite of "turgid". The contents
of the potato cells shrink and pull away from the cell wall.
cells are said to be plasmolysed. When plant cells are placed in a
solution which has exactly the same osmotic strength as the cells they
are in a state between turgidity and flaccidity. We call this
incipient plasmolysis. "Incipient" means "about to be".
When a cell is placed in distilled water (high water concentration)
water will move across the semi-permeable membrane into the cell
(lower water concentration) by osmosis, making the cell swell. This
cell is now referred to as turgid. If done with potato cells the cells
would increase in length volume and mass because of the extra water.
If these potato cells were placed in a solution with a low water
concentration, then the opposite would happen. Water would move out of
the cell into the solution. In extreme cases the cell membrane breaks
away from the cell wall and the cell is referred to as plasmolysed.
The potato cells will have decreased in length, volume and mass.
Osmosis will occur across a semi-permeable membrane whenever there is
a difference between the water concentrations on the two sides of the
membrane, and knowing that when this happens to cells they will either
become turgid if water flows into them or if water flows out of them,
and thus change their volume.
Planning: In this experiment I will be trying to find out the osmotic
properties of a potato. To do this I will cut out several pieces of
potato to the same length and then place them in different molarities
of sugar solution. Fill some test tubes with 30ml of the selected
molarity solution. Then slice out sections of the potato. Cut these
sections in length exactly the same so that all the potato samples are
the same size and therefore should be the same weight. Then I will
take a variety of molar sugar solutions; I have selected 2%, 4%, 6%,
8%, 10% and distilled water. I will place the potatoes in the test
tubes for 24hours weigh the potato and record each samples results.
Immediately afterwards I place the sample inside the test tube I will
cover them with cling film to stop the sugar solution from evaporating
away. Then leave the test tubes in the bathing solution for about 24
hours and then retrieve each sample and roll them briefly on a piece
of tissue to get rid of the excess water. Then weigh them straight
away to stop the sample losing any more water that would produce
inaccurate results. The two variables in this experiment would be the
different molarities of the sugar solutions and the changing weight of
each potato sample.
Aim: To investigate the effect of varying concentration of a certain
sugar solution on the amount of osmotic activity between the solution
and a potato chip of a given size.
Factors and fair test: If I am going to make this a fair test, then I
will have to control these other factors like I mentioned below:
The main factors which will need to be considered whilst doing the
« Temperature of water: Doing the tests at one fixed temperature will
control the temperature of the water. For the purpose of my experiment
I am going to do all the experiments at room temperature.
« Size of chip: The size of the potato is very important. This is
because if the size of the potato varies, so will the amount of mass
it can loose or gain. I am going to try to cut all the pieces of
potatoes, to the same size. Because of the 'chipper´ I will have chips
with the same weight at 3g, but the chip will be 3cm.
« Light: The light intensity will be mostly constant as the chips will
not be moved whilst being stored.
« Mass of potato: The mass of the potato is a variable, and this means
that it will be measured throughout the experiment. I will measure the
mass in grams. The potato chip will be measured before it is put in
the solution, and after. This will allow us to see whether osmosis has
taken place, and how much osmosis has occurred.
« Volume of solution potato is: The volume of the solution that the
potato chips are kept in must be the same. The chip must be totally
covered in the solution, and the amount of solution will be kept the
same because all the chips are the same size. The amount of solution I
cover each chip in will be 30ml.
« Type of potato: The type of potatoes I will use is going to be kept
the same, because different potatoes may absorb at different rates.
For this experiment I am going to use the same potato.
« Time left in solution; the time the potato chip is left in the
solution must be kept the same for each chip. This is because more or
less solution may be absorbed depending on time. I am going to keep
each potato chip in each solution for 24hours.
« Surface area of potato chip: The surface area of the potato chips
will be kept the same by having all the chips the same size. This must
be kept the same because the amount of surface area exposed to the
solution may affect the rate of osmosis. The thickness of the chip
will already be the same, so I will cut the length of each chip to 3cm
« Using the same balance to measure chip: To make the mass readings
fairer, I will take each chip, roll the chip gently on a paper towel,
to remove all excess solution, and I must not squeeze the chip. I am
also going to use the same balance to weigh my chips. This is because
the measurements may vary slightly between scales.
Hypothesis: Osmosis is defined as the net movement of water or any
other solution's molecules from a region in which they are highly
concentrated to a region in which they are less concentrated. This
movement must take place across a partially permeable membrane such as
a cell wall, which lets smaller molecules such as water through but
does not allow bigger molecules to pass through. The molecules will
continue to diffuse until the area in which the molecules are found
reaches a state of equilibrium, meaning that the molecules are
randomly distributed throughout an object, with no area having a
higher or lower concentration than any other. For this particular
investigation I think that the lower the concentration of the sugar
solution in the test tube the larger the mass of the potato will be.
This is because the water molecules pass from a high concentration,
i.e. in the water itself, to a low concentration, i.e. in the potato
Therefore, the chips in higher water concentrations will have a larger
mass than in higher sugar concentrations. I predict that the higher
the concentration of sugar in the solution, the more water will move
out of the potato chip. Therefore the distilled water solution will
has the greatest mass and the higher the concentration that the chip
is exposed to, the more water will move out of the chip; making it
flaccid so the 10% chip will become flaccid.
« Distilled Water
« 30 ml Sugar Solution at 2%, 4%, 6%, 8% and 10%
« 12 test tubes
« Cling Film
« Top Pan Balance
« Paper Towels
« Measuring Cylinder
Method: in order to do the following experiment I will be following
1. Collect all the apparatus.
2. I will carefully slice twelve bits of potatoes at the measurement
of 3cm and weigh them at 3grams on the top pan balance.
3. I will label all the test tubes so the solutions don't get mixed
4. Using a measuring cylinder I will pour all the concentrations at
30ml in the correct tubes.
5. After placing the potato in the tubes I will cover them with cling
film and leave them for 24hours.
6. 24hours later I will remove all the cling film and dry the potatoes
with a paper towel.
7. I will then measure all the potatoes and record the results in a
The experiment must be repeated twice: the experiment may look like
Preliminary Work: Prior to this experiment I did an experiment to help
with a prediction and also to help indicate a number and range for the
main experiment. The results from this experiment had many errors
occur due to humanly errors. Whilst doing the experiment we didn't dry
the top pan balance before we measured the chips and we also forgot to
dry the potato chips. This caused all are results to be inaccurate
also we decided to vary our solutions more. When we did out
preliminary experiment we only used 2%, 8%, 10% and distilled water.
This didn't give us a good range of results and caused the whole
experiment to weaken.
We also tried different masses for the potato chips and came to the
conclusion three grams would be adequate. From the preliminary
experiments we decided to vary the solutions more so we could monitor
the way osmosis works clearer. So in our real experiment we decided on
3grams for the potato chips and try the 4% and 6% solutions as well.
We also learn in the real experiment it's necessary to dry the potato
chip before measuring. The results below show the preliminary results
as you can see they are inaccurate. Doing this preliminary experiment
helped us improve our real experiment greatly.
Mass before (g)
Mass after (g)
Change in mass (g)
% change in mass
Obtaining your evidence: Whilst we were doing the experiment I was
fortunate as I was able to follow the method.
Mass before (g)
Mass after (g)
Change in mass (g)
% change in mass
Mass before (g)
Mass after (g)
Change in mass (g)
% change in mass
[IMAGE]I used the formula: change in mass
Mass before X 100[IMAGE]
Conclusion: I have decided to draw both graphs for the results and
make a decision when I see the result of both. The graph which looks
more accurate is the one I will analyse. Drawing both graphs I have
come to the conclusion that the second experiment is more accurate as
there seems to be less errors then the first experiment by far. In the
first experiment the gradient isn't steep as it should be.
The graph shows what was obtained when the concentration of the
solution is plotted against the percentage change in mass. At point D
the graph tells the viewer that no osmosis has occurred, suggesting
that the concentration of water inside the cell is equal to the
solution outside. At point A and B (high water concentration), there
is indication that the cell is increasing further in size. This is
because the cell is fully turgid and no more water can enter. At point
E and F (high water concentrations), there is indication that the cell
is decreasing further in size. This is because the cell is going
However, there is a pattern on my graph, and this is as the
concentration of the solution increases, the percentage change in mass
decreases. The graph shows that the percentage gains and loss in
inversely proportional to the concentration. The gradient does change
in my graph. It gets less steep as X axis gets bigger. This is because
the potato chip is becoming as flaccid as it possibly can, and so the
change in mass of each molar concentration is becoming closer and
It shows that the potato cells increase in mass in solutions with a
high water concentration and decrease in mass in solutions with a low
water concentration. When the concentration reaches above 10%, there
appears to be no further water loss, suggesting that the cell is fully
plasmolysed. From the graph an estimate to the concentration of the
potato cell can be made at 6% as this is the point where the potato is
not increasing or decreasing in mass, this is known as the isotonic
point. This is where no osmosis is taking place; both the potato and
the solution have an identical molar concentration. The next point E
looses approximately 0.333%. This shows that the water potential of
the sugar solution in the beaker is weaker than that of the potato
chip. The next, 10%, looses approximately 0.33% in mass. This shows
that the sugar solution has a weak water potential and that osmosis
took place. This is why the potato lost even more mass, and it shows
that the water potential in the beaker is less than that of the potato
chip. This pattern carries would carry on through the graph if there
was more range of Molars, and even more mass is lost, as more water
moves out of the potato into the solution.
This graph of the change in mass helps prove the point of complete
plasmolysis, whereby the potato cannot expand and take in any more
water. As you can see as the molar concentration increases the change
in mass decreases. From right to left the first two points on the
graph are very spread out indicating that there was a large change in
the mass. This decreases throughout the increasing molar concentration
until the change is minuscule.
This graph shows a clear indication that there was an overall increase
in mass during the experiment. At point D the percentage increase and
decrease is separated.
My results also match with my initial predictions.
Evaluation: There were not many out of the ordinary results in the
second experiment, but some were not as close to the line as others.
There was anomaly which was circled in the graph and didn't fit in
with the pattern. This may have been caused by human errors. When the
potato chips were removed from the test tubes and dried I may well
have dried some potatoes more thoroughly than others and so some would
have more excess water, which would add to the mass. If the experiment
was repeated I could find another way to dry the potatoes that would
ensure that all were dried in the same way for the same time. However
with all this said I think that the experiment was successful and I
was very pleased with the complete comparison of my results with my
However I do believe the first experiment went awfully wrong as the
results were all inaccurate as they didn't follow the pattern of
osmosis. This could have been to a number of factors such as the
surface area also there may have been an error with the molar
The cutting of the potatoes was the most difficult part of the
experiment as although I was recording my results by mass, it could
well have affected the surface area and so the overall rate of
osmosis. If I were to repeat the experiment I would have possibly
found a machine to cut the potato as it would ensure that all potatoes
would be the same in weight and dimensions. As well as the potato I
could have found a more accurate way to measure out the solutions and
to determine the molar concentrations. Perhaps I could have used a
burette. This would ensure that I have an accurate amount of fluid in
each test tube. I could also weigh each chip on a more accurate scale,
e.g. not to 0.00g but to 0.0000g.
The accuracy of the experiment was accurate to suit our purpose to
make it more accurate several steps could have been taken.
1: Human error: Human error could have been reduced by taken more
accurate measurements to a uniform result. This could be attempted by
using a tool which could be set to a set length to cut the potato.
2: If the potatoes did not rest against the sides then they would all
have the same amount of surface area. This is the same for the potato
samples that float therefore exposing them to air and the samples that
sink stopping osmosis occurring on the areas that are touching the
bottom of the test tube.
Reliability: The results were reliable to take a reasonably accurate
result. However the steps above (1, and 2) would produce an even more
Further work: To extend this experiment it could be repeated exactly
as before. However this time results at the morality levels. This
would produce much more accurate results.
Other variables in the experiment could be changed for example instead
of changing the weight of the potato the species of the potato could
be changed. For example new potatoes, King Edwards etc could be used.
Also the shape and size could be changed. However this would not
affect the results much. This is because the variable would only
change the rate of osmosis because of a different weight and size.
Temperature could also be changed for example the samples could be
placed in different water baths and brought up to different
temperatures to see if temperature played its part in the osmosis of
potatoes. 5 sets of 5 potatoes could be placed in water baths at 10oC,
20oC, 30 oC, 50oC and 60 oC. Then leave them for 24 hours making sure
all the variables in the first experiment still apply however just
using one molar solution. Then after 24 hours re-weigh the samples and
record the result. I would expect that at high temperatures the potato
samples would osmosise the most. This is because at high temperatures
the solutions water molecules would move faster and therefore equal
the concentration faster. A preliminary experiment could be set up
beforehand to find out how long the experiment should be kept going
because if the concentration of the potatoes equalises then the weight
of the potatoes will be almost exactly the same.
I could extend my coursework by testing the same brand of chip using a
different substance. By this I mean using a different thing instead of
sugar, i.e. salt or coffee or even vimto. Then I could find out
whether osmosis occurs differently with different things diluted in
the water. I could even use different vegetables.