This document describes an experiment on osmosis. Dialysis bags containing different concentrations of sucrose solution (20%, 40%, 60%) and water were placed in beakers of water or 40% sucrose solution. The bags were weighed every 10 minutes over 80 minutes. Results showed the rate of osmosis was greater when the concentration difference between the bag and beaker was higher. The 60% sucrose bag gained the most weight due to the largest concentration gradient. Improving the measurement of bag and clamp weight could increase the experiment's accuracy.

1. Osmosis 1
OSMOSIS
By: Shelby Lazorka
Lab Partners: Laurel Miner and Kristi Raible
Biology 120-949
Professor Aguayo
October 31, 2012

2. Osmosis 2
OSMOSIS
INTRODUCTION:
By definition, osmosis is the diffusion, or dispersion, of water through a selectively
permeable membrane from a higher concentration to a lower concentration (Campbell, pg.132).
There are many different factors that can affect the rate of osmosis such as temperature, particle
size, and the size of the concentration gradient. A higher temperature can cause osmosis to occur
at a much faster rate because the molecules are more likely to pass through the selectively
permeable membrane quicker than they would at a lower temperature due to the molecules’
higher energy. In addition, the size of the particles can affect the rate of diffusion through the
membrane. Without this diffusion, osmosis cannot take place. In the experiment, the sucrose
molecules are too large to pass through the dialysis bags while the water molecules are easily
able to move freely in and out due to their small size. Lastly, the magnitude of concentration
gradient can greatly affect the rate of osmosis due to the fact that the more hypotonic or
hypertonic a solution is, the faster the movement of water molecules and other particles. With
more of the solute in the dialysis bag, the amount of water molecules in the bag as compared
with the amount in water molecules in the beaker of just water is much lower. Water molecules
move from areas of a higher concentration to a lower concentration to move down their
concentration gradient. Because of this, the water molecules will move at a faster rate during
osmosis and diffusion. The magnitude of the concentration gradient will play the biggest role in
this experiment.
A permeable membrane is a type of membrane that only allows certain molecules to pass
through it. The selectively permeable membrane in this experiment was the dialysis bags.

3. Osmosis 3
However, as stated by Hawthorn, a semi-permeable membrane is not absolutely necessary for the
demonstration of osmosis. The concentration within a cell can change merely by the splitting of
larger molecules into smaller ones, or the reverse. (1930) Two objectives in this experiment were
to show the effects of osmosis and to show how one variable can affect the rate at which osmosis
takes place.
METHOD AND MATERIALS:
In this experiment, five dialysis bags were used. My lab partners and I placed clamps on
both ends of each of the tubes to keep the solutions in their bags and in their rightful place. Two
of the dialysis bags contained tap water. The other three solutions inside the bags were 20%
sucrose (at least 10mL), 40% sucrose (at least 10mL), and 60% sucrose (at least 10mL). To
perform this lab, we prepared each of the five bags with their designated sucrose solution. In this
experiment, the dialysis tubing acted as the selectively permeable membrane. The dialysis
tubing allowed the passage of water molecules only because the sucrose molecules are too large
to pass through the membrane. We then placed the bags into five separate beakers. Four of these
beakers contained only tap water and the fifth contained a solution of 40% sucrose.
We filled the first dialysis bag with 10 mL of tap water. Next, we filled the second bag
with 10 mL of the 20% sucrose solution. The third bag was filled with 10 mL of 40% sucrose
solution while the fourth bag was filled with 10mL of 60% sucrose solution. The final bag was
also filled with 10 mL of tap water. We made sure that when filling these bags that we removed
as much air as possible before clamping off the end of each of the bags. In addition, we made
sure that all of the bags were soft and floppy instead of firm to insure that experiment would
work properly. Next, we placed the dialysis bags one through four in there own separate beakers

4. Osmosis 4
filled with tap water. But, our fifth bag full of tap water was placed in a beaker filled with just
enough of the 40% sucrose solution to cover the bag. All of the bags remained in their designated
solutions for 90 minutes. However, all of the bags were quickly removed every ten minutes to
weigh and record each of their masses with the same scale every time. Before weighing the bags
after they were removed from the respective solutions, we had to blot them dry to minimize
error. After all the data was collected, we had to use a corrected cumulative change in weight
equation to fix any variations in our data. For this equation, every time a weight was recorded,
we had to subtract it from the weight of the bag prior to the one being measured.
RESULTS:
The rate of osmosis was greater when there was more of the hypotonic solution in the
bag. On the contrary, the more hypertonic the bag in a sucrose solution, the more the mass of the
bag decreases. The graph shows the differences in the corrected cumulative change in weight in
grams of the four bags over the 80 minutes of time given because our group could not obtain data
for the last 10 minutes of the experiment. The bag containing the 20% sucrose solution gained
the least amount of weight because it had a lower concentration of sucrose. The water diffused
into the bag at the slowest rate. The 40% filled sucrose bag gained more weight than the 20%
sucrose bag because the concentration of sucrose was larger and thus, contained less water then
in its beaker. The water diffused into the bag at a quicker rate than the 20% sucrose solution.
The bag that contained the most weight was the 60% sucrose bag due to the fact that it had the
largest difference in concentration of sucrose to water and the water diffused the quickest across
the membrane.

5. Osmosis 5
DISCUSSION:
Our graph showed that the 20% sucrose bag gained 3.2g of water over the course of our
80-minute experiment. Also, the graph showed that the 40% sucrose bag gained 5.7g of water
over 80 minutes. The 60% sucrose bag gained 9.1g of water and the bag of water in the 40%
sucrose solution lost 4.3g of water. In this experiment, the magnitude of concentration of the
sucrose solution increased as well as the average weight gain of the bag of sucrose concentration.
One change that could be made to make the experiment more accurate and precise would
be to record the mass of the clips and the dialysis bags at the same time. This way, the mass
could be truly precise instead of somewhat correct. The weight of the clamps and the bags could
be subtracted from the total overall weight with the amount of water that travels in and out of
each of the bags, making the measurement of the water more accurate and precise.

6. Osmosis 6
References
Campbell, Reece, Urry, Cain, Wasserman, Minorsky, & Jackson (2008). AP Edition
Biology (8th ed.). San Francisco, CA: Pearson Benjamin Cummings.
Hawthorne. Diffusion, Osmosis and Osmotic Pressure. The Scientific Monthly. (1930) 31.6.
535-542.

7. Osmosis 6
References
Campbell, Reece, Urry, Cain, Wasserman, Minorsky, & Jackson (2008). AP Edition
Biology (8th ed.). San Francisco, CA: Pearson Benjamin Cummings.
Hawthorne. Diffusion, Osmosis and Osmotic Pressure. The Scientific Monthly. (1930) 31.6.
535-542.