1. Biology teacher support material
Investigation 1
Water Potential of Potato and Sweet Potato; the Weighting Method.
Research Question: How will the weight vary between the sweet potatoes and potatoes when
placing each sample in different concentration solutions?
Hypothesis: When placing samples in hypertonic solutions they will loose weight. And on the other
hand when they are going to be placed in hypo tonic they will gain weight. But the difference in
weight will vary in potato and sweet potato since the sweet potato tastes sweeter and it has a higher
sugar solution.
Variables: Dependent: - Percentage % (difference in weight)
Independent: - Initial Weight of Potato (grams)
- Final Weight of Potato (grams)
Controlled: - Molarity (0,0; 0,25; 0,50; 0,75; 1.0)
Volume of the solution to submerge the potato
Potato cylinder size
Room temperature (19°C.)
Materials:
Big Potato
Cork Borer
Solutions of water and sugar (Molarities: 0,0; 0,25; 0,50; 0,75; l,0)
Blotting Paper
Electronic Balance
Test Tubes
Test Tube Racks
Procedure:
l) Five test tubes were labelled, each one with the different molarity of the
solutions: (0,0; 0,25; 0,50; 0,75; 1,0)
2) The tubes were filled with the different concentration solutions, according to what was
previously marked, up to three quarters of the tube.
3) With a cork borer five potato cylinders were cut and placed over five different 'blotting
papers that were labelled with the 5 different concentration solutions randomly.
4) The potato cylinders were dry up and weighed on an electronic balance and then
placed in the test tube with the solution according to the concentration describes at the
blotting paper.
5) All the initial data was recorded on a previously prepared table.
6) The samples were left for a day in the test tube racks so the process took place.
7) The next day the potato cylinders were taken from the test tubes and placed on blotting
paper labelled with its respective molarity.
8) The cylinders were weighed and the final data was recorded on the table.
9) The steps were repeated but instead of using potato, this was replaced by sweet potato.
10) Calculations and graphs were prepared.
11) Conclusions were drawn to prove the hypothesis.
© International Baccalaureate Organization 2007 1

2. Biology teacher support material
Investigation 1
Data collection:
Potato in different concentration solutions.
Molarity Initial weight (grams) Final weight (grams) Difference in weight Percentage %
±0,1g ±0,1g (grams) ±0,1g (difference in
weight)
0 0,9 1,3 0,4 44
0,25 0,9 1,2 0,3 33
0,50 1,0 0,7 -0,3 -30
0,75 1,0 0,8 -0,2 -20
1,00 1,1 0,6 -0,6 -54
Sweet potato in different concentration solutions
Molarity Initial weight (grams) Final weight (grams) Difference in weight Percentage %
±0,1g ±0,1g (grams) ±0,1g (difference in
weight)
0 0,8 1,2 0,4 50
0,25 0,8 1,1 0,3 37
0,50 0,9 1,4 0,5 55
0,75 1,0 1,1 0,1 10
1,00 1,1 0,9 -0,2 -18
Graph:
Potato and Sweet Potato Solute Potential
80
60
Percentage (%) of difference in weight
40
20 0,1M = -3,0kpa
0
0 0.2 0.4 0.6 0.8 1 Sweet 1.2
-20 potato
0,45M =
-40 -1,3kpa
Potato
-60
-80
Molarity
"
2 © International Baccalaureate Organization 2007

3. Biology teacher support material
Investigation 1
-3-
Conclusion:
After doing the work and collecting relevant data to know if my hypothesis was right or wrong, I can
state that in my case, by determining my observations my hypothesis was correct because when
placing samples in hyper tonic solutions they loosed weight, and on the other hand when placing them
in hypo tonic ones they gained weight respecting the potato solute potential which is -1.3 kPa and the
sweet potato -3.0 kPa. As I predicted there was a difference in the resulted weights between the potato
and the sweet potato, potato gained more weight since the line is moved to the left of the graph. This
occurred because of the sucrose that the sweet potato contains it will obviously gain more weight in
hyper tonic solutions than potato and gain loose weight in hypotonic solutions. This process basically
occurs by osmosis, that is when substances move from a place of low concentration to a place of a
higher concentration through a semi permeable membrane. The differences in results between potato
and sweet potato are because of the sucrose that sweet potatoes contain.
Although the experiment resulted successful there are several problems that appeared along the work
that could certainly be improved so that the results become more accurate. One of the observations
that was clearly pointed out was the exact measurement of potatoes, although we used an electronic
balance the weight isn't exact and that may cause marginal errors. A possible improvement for this
could be to try and be as precise as possible to be exact with measurements, but obviously we don't
have the possibility of getting more exact balances. Other problem that surged along the experiment
was the lack of samples, of course that doesn't depend on us that's just because we don't have enough
time to dedicate to each experiment, so that more samples are used. Other important factor that could
have influenced in our work is the way we dry up the samples after extracting them from the solutions,
although we've tried to do this as equal as possible with each sample its quite difficult that the samples
result dried up all the same. A possible solution for this problem may be not to dry the samples up and
used them just as they are taken from the solution.
But besides of the observations that I made and the errors that we made, we could finish the work and
obtain reasonable and relevant data to determine how diffusion occurs at hyper and hypotonic
solutions according to the sample placed in each.
© International Baccalaureate Organization 2007