Investigating the Effects of Sucrose Concentration on the Mass of Potato Chips
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The aim of my experiment is to investigate the effect of varying the
concentration of sucrose on a potato chip. I aim to observe the change
in mass, and I hope to view what happens to the chips as the
concentration increases, and I hope to see the effect that osmosis has
on the chip.
The experiment that I am conducting uses the process of osmosis.
Osmosis is the movement of water molecules across a partially
permeable membrane from a region of high water concentration to a
region of low water concentration. Partially-permeable membranesare
very thin layers of material which allow some substances to pass
through them but prevent other substances from passing through. For
example, a partially permeable membrane may allow water molecules to
pass through it, but may not allow larger molecules such as Glucose to
pass through. An example of a partially permeable membrane is visking
tubing, which is also known as 'dialysis tubing.' Visking tubing is a
partially permeable membrane with tiny pores, which allows small
molecules such as water to pass through but does not allow larger
molecules such as sugar. If solutions of different concentration are
on either side of the visking membrane, water molecules will pass
through and tend to dilute the more concentrated solution, hence the
idea of osmosis. Below is an example of osmosis. There is one section
of a beaker containing a solution of water and glucose molecules. The
other side of the beaker contains just water molecules. In between
both liquids is a partially permeable mebrane separating the two.
Partially permeable membrane.
THE NET MOVEMENT OF WATER MOLECULES
Cell membranes are exactly the same as partially permeable membranes.
Cell membranes will allow small molecules like Oxygen, Water, Carbon
Dioxide, Ammonia, Glucose, amino acids, etc. to pass through. Cell
membranes will not allow larger molecules such as Sucrose, Starch,
protein, etc. to pass through.
If you place a plant cell, or even an animal cell in a medium,
different things could happen to it depending on its situation. If the
water concentration of the cells cytoplasm is lower than the
concentration of the medium surrounding the cell, which is a hypotonic
solution, then osmosis will result in the cell gaining water. As this
carries on, it could result in swelling up the cell or even bursting
it. This is because the water in the cell comes in faster by osmosis,
than it leaves the cell by diffusion. If the water concentration
inside the cell is the same as that of the surrounding medium, which
is now an isotonic solution, a dynamic equilibrium will occur between
the number of molecules of water entering and leaving the cell. This
basically means the rate of osmosis is even on both sides of the
partially permeable membrane. By doing this, the size of the cell will
remain the same. If the concentration of water inside the cell is
higher than that of the medium, which is now hypertonic, then the
number of water molecules diffusing out will be more than that
entering, and therefore the cell will shrink and shrivel due to
Plant cells have a strong cell wall surrounding them in comparison to
animal cells. When they consume water by osmosis they start to swell.
The cell cannot burst as it is protected by a cell wall which
regulates the concentration inside the cell. If the concentration is
high, then the cell wall will release substances. If it is too low,
then the cell wall will allow substances to enter. Plant cells become
turgid when they are put in dilute solutions. The pressure inside the
cell increases, and eventually the internal pressure of the cell are
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 arouse into the sunlight.
When plant cells are placed in concentrated sugar solutions, such as
sucrose, which I am studying, then they lose water by osmosis and they
become flaccid, which is the total opposite of turgid. After placing
the plant cell in sugar solution, the cells become plasmolysed. This
is the process of plasmolysis. This basically means that the contents
of the cell have shrunk, and moved away from the cell wall. The
vacuole shrinks due to loss of water, and the cytoplasm peels away
from the cell wall.
But these cells only become turgid and flaccid in those conditions.
When plant cells are placed in a solution which has exactly the same
osmotic strength as the cells, they are in a position between
turgidity and flaccidity. This is called incipient plasmolysis.
"Incipient" basically means that they are about to be something.
When putting a potato chip in a medium, either one of two things could
happen. The potato chip could either loose mass or gain mass. It will
loose mass if the concentration of water is higher in the potato chip,
than it is in the medium. So therefore, I think that if the
concentration of sucrose is less that means that there is a higher
concentration of water in the liquid, meaning the net movement of
water molecules will be from the solution, to inside the potato chip,
which will lead to a gain in mass of the potato chip. If the sucrose
solution has a higher concentration of sucrose, than this means that
the concentration of water will be less, meaning that the water
molecules from inside the potato chip will diffuse by osmosis out of
the chip, therefore the net movement will be from the chip to the
solution, resulting in a loss of mass.
Underneath my method you will find a list of apparatus which I used to
conduct this experiment/investigation.
I will start by collecting all my apparatus which can be found on the
following list. I am going to use three test tubes for each
concentration of sucrose so that I can get an average, and therefore
it will be a fair test. I will fill my test tubes to the 20ml point
with the given amount of sucrose concentration, which is either, 0%,
10%, 20%, 30% or 40%. The reason for these different amounts is so
that we have a fair test, and so that we can see the affect of
increasing concentration. I will then label them to prevent confusion.
The volume of solution will stay the same at all times, at 20ml, so
that the concentration gradient is the same. I will then cut out
cylinders from my potato chips using a cork borer. At this point the
potatoes will be on the white tile. I will cut them into equal lengths
of 50mm using a ruler and a scalpel. The reason why they have to be
equal lengths is to keep a fair test. I will weigh my potato chip on
the top pan balance before I do anything and record it. I will then
place the potato chip in the medium and leave them for 24 hours. I
will weigh the potato chip once again using the top pan balance, the
following day, and record it. Before I do that though, I will blot of
the excess water from the chips to prevent an extra mass. After
obtaining all my results, I will use the following formulae to work
out the percentage change in mass:
In my experiment, I will keep these the same:
· The surface area of the potato chips, therefore the same lengths.
This can be done using a ruler.
· 20ml of solution in the beaker for each experiment.
· The same person timing, and conducting the experiment.
· The same beaker, (washed after each experiment.)
These are the variables:
· The concentration of sucrose in the solution:
0%, 10%, 20%, 30%, and 40%
· Wear a lab coat at al times during the experiment to protect
clothing and skin.
· Be careful with sharp instruments such as the cork borer. Hold them
by the handle, and keep away from eyes, and other people.
· Bags and coats under the tables to prevent people falling over, and
· Be careful when pouring the hot water from the kettle.
[IMAGE]List of apparatus:
· 15 x test tubes (With Lids)
· Test tube rack
· Sucrose solution
· Stop watch
· Cork Borer
· [IMAGE] [IMAGE]White Tile
· Electronic Top Pan Balance
These are the results I gained during the experiment. I have shown
them in a results table and a scatter graph.
Sucrose Concentration (%)
Initial Mass of Potato Chip
Final Mass of Potato Chip
% Change in mass
(Scatter Graph on next page)
My results have come out as expected in the prediction. I stated that
as the concentration of sucrose increased, the rate of osmosis from
the potato to the sucrose solution would increase. As you can see this
is true. The first sucrose solution of 0% is mostly known as water. So
therefore, this is the only situation where the net movement of water
molecules is from the sucrose solution to the potato. Despite this
concentration, the other concentrations worked out fine. In the 10%
sucrose solution test, the mass of the potato decreased by 3%. As the
concentration got higher, the mass of the potato dropped more rapidly.
This is simply because of particles. If the concentration is low (10%)
then there is a fair amount of water particles and sucrose particles.
At this point, the water particles inside the potato are at a higher
concentration than there is in the solution, therefore osmosis takes
place from the potato to the solution. If the sucrose concentration is
even higher (40%) then the concentration of water particles is even
higher in the potato, meaning the rate of osmosis is faster.
My test could have been improved by using different apparatus. For
example, we could have used a lot more hi-tech equipment, such as data
logging equipment or scientific computers to conduct the experiment. I
could have also repeated my test a dozen times to be sure and also to
create a fair test. The reason that these ideas were not approached
was because it is time consuming to repeat the experiment so many
times, and it is too expensive to buy such hi-tech equipment.
I think that I could have improved in one or two areas; such as wiping
of the excess water from the potatoes using a towel. The towels could
have either wiped off and absorbed a bit of water or just pushed the
water into the potato. If this did happen, then it would change the
mass of the potato. Another way of improving the results would have
been to leave the experiment running longer, this would have enabled
me to find the saturation point (when the potato can no longer take in
any more water) and dehydration point (when the potato cannot lose any
more water)and therefore get a more accurate result.
Basically, my test was a success, as the results and graph shows. I
did not get any anomalies, and I did not make any mistakes.