The purpose of this experiment was to find

The purpose of this experiment was
to find the osmolarity of the potato.  It
has been concluded that the osmolarity of the potato is about 0.84
osmol/L.  The osmolarity of the potato
was derived by calculating the point at which the trend line intersects the
x-axis.  When the potatoes were placed in
a solution with a glucose concentration of 0.0M, an increase in the percentage
mass of the potatoes was observed.  This
showed that the solution was hypotonic, as there was a lower solute
concentration outside the cell than inside the cell.  During the process of osmosis, molecules moved
through a semi-permeable membrane from an area of higher concentration to lower
concentration in order to balance the concentration of solvent.  Water, which acted as the solvent, moved into the
potato as it had the higher solute concentration and this balanced out the amount
of solute molecules. When the potatoes were placed in solutions of glucose
concentration ranging from 0.2M to 1.0M, the percentage mass of the potatoes
decreased.  The decrease in mass led to
the deduction of hypertonic solutions.  The
high solute concentration in the glucose solution caused water to be drawn out,
acting as the solvent, from the potato and into the glucose solution in order
to create a balance of solute molecules between the two. Water permeated into
the glucose solution from the potato, causing it to lose mass. Being a large
molecule, glucose (C6H12O6) cannot move
through the semi-permeable membrane as easily as water.

 

In order to find the osmolarity of
the potato, it required finding the point at which the solution would be
isotonic.  When the solution is isotonic,
the concentration of glucose would reach an equilibrium with that in the
potato, meaning the point when the mass change of the potato was zero needed to
be found. This was found by setting the equation of the line (y = -40.727x +
3.4246) to 0 and solving for x.  The
osmolarity of the potato was derived through this process.  It should be noted that this is an approximation
rather than the actual osmolarity of the potato.  The value
of the line of best fit, was 0.92742. 
The closer the  value is to 1, the stronger the correlation is
between the data points.  Even though
there was a strong negative correlation within the data, it should not be used
to determine exact results, but more as a guideline as to what the osmolarity
of a potato is.  The negative correlation
is consistent with the results, as the solute concentration increased, the
percent mass change decreased.  A linear
relationship best represents the data, as the 1st differences
between each average percent mass change is constant, except at the
concentration 0.6M where there is an anomaly.

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Percentage mass change was chosen
to represent the data as it shows the increases and decreases in the mass of
the potato, which is all relative to each other.  This shows the extent of the change.  To calculate percentage change in mass, you
subtract the initial mass by the final mass and divide the difference by the
initial mass.  This is a better
indicator, showing the extent that the glucose solution has changed the potato
based on the percentage mass change, when the difference is divided by the
initial mass.  The mass of all the potato
samples are different as they are uncontrolled variables within the
experiment.  With varying masses, the
rate in which water moves will be different. 
Percentage differentiates which tissue’s mass had greater or smaller
increases as it is a ratio rather than the absolute value. 

 

 

Evaluation:

 

Overall, the results of the lab
were reliable.  The method allowed for a
reliable collection of data.  The amount
of solution and the size of the potato was a sufficient amount that allowed the
two substances to interact with each other. 
There was good precision within the data as most of initial and final
masses of the trials were consistent. The standard deviation was relatively low
for all the trials, ranging from 1.09 to 9.59. 
The majority of the standard deviation from the trials were below
2.5.   At 0.0M glucose concentration
there was an anomaly in the accuracy of the data, as the percent mass change
ranged from 13.6 to -13.0.  This
especially odd at that concentration, as negative mass change is contradictive
to osmosis. The 1st differences which calculated the difference between each
average percent mass helped define the graph as having a linear
relationship.  This means that a change
in the independent variable will produce a corresponding change in the
dependent variable. The  value of 0.92742 also refers to the
correlation of the points to one another. 
The stronger the correlation, the closer to 1 the  value will be.

 

 

A source of error within the
experiment was random variation.  It was
present in the mass of the potato since different potatoes were used.  Different potatoes have different water
concentrations, leading to a variation in weight which could impact the results
for osmolarity.  This can be improved by
using sections from the same potato for each trial, which will create more
unity within the data. The errors in each percentage mass change varied
depending on the concentration of glucose used. 
The vertical error bars significantly varied in length, each with
different standard deviations. Random errors can be reduced by conducting more
trials and also be lessened if the same person conducted all the trials. There
would be unity in the way that the data is interpreted. Human errors occurred
in the collection of data.  Small groups
of 3 were assigned to do the trials for each glucose concentration which lacked
consistency as the same person conducting each trial would allow for more
certainty.  Systematic error occurred
when the initial mass of the potato was recorded.  There was a variation in the initial masses
for the potato which creates a bias in the data, as the potatoes masses do not
all start at the same point.  Some of
this error was eliminated by measuring the percent mass change rather than the
actual difference in mass.  Another way
to lessen the likelihood of this error would be to use the same scale to
measure all of the potato masses.

The uncertainty was determined to be ±0.01 since the results of
each trial were recorded up to 3 significant figures and 10% of the last figure
was determined to be a sufficient error margin.

 

Accuracy in reference to the
validity of the experiment cannot be measured as there is no standard value of
the osmolarity of potatoes to compare the conclusions and data of the
experiment to.  Without any comparisons
or a percent error value, the results from the experiment are subjective. It
only showcases one set of values which needs to be mediated by others to
diminish the extent to which random errors affect the data and ensure
accuracy.