Diffusion and Osmosis of Starch and Simple Sugar Macromolecules:
Determining the affect size has on diffusion rate in a period.
Principles of Biology 2107
February 2019
Abstract
The experiments discussed in this report were completed to determine the ability of macromolecules to
diffuse through a semi-permeable membrane and the affect that time and rate in relation to size has on
diffusion as well as osmosis. The experiments dealt with two specific molecules simple sugar and starch.
The end results of the experiments were inconclusive, did not confirm nor negate the hypothesis, and
therefore require further experimental trials with other macromolecules.
Introduction
Diffusion is a simple process in which molecules, ions, atoms, and other microscopic particles in the
body move between a semi-permeable membrane from an area of high concentration to and area of
lower concentration to obtain a state of equilibrium within and outside the membrane. There are
different kinds of diffusion such as osmosis, facilitated diffusion, and passive diffusion. Osmosis focuses
on water molecules and diffusion that takes place in water; once again moving from an area of high
concentration to an area of low concentration with the end goal of reaching equilibrium. facilitated
diffusion and passive diffusion focus on moving other molecules with some minor difference. Molecules
and/or ions undergoing facilitated diffusion move across the semi-permeable membrane with the help
of integral protein channels, like a train moving between stations via a tunnel, where as in passive
diffusion molecules move across this membrane with no assistance. Cells use diffusion and osmosis to
transport enzymes, proteins, charged molecules and other nutrients to specific areas of the body.
The kidneys, for example, use diffusion and osmosis to filter the liquids you’ve taken in, keeping the
good and secreting the bad in the form of urine. If you ‘ve ever consumed high amounts of alcohol,
coffee, sugary beverages, energy drinks, or electrolyte replacement drinks, you’ll notice that your body
will crave more and more water. This is because most of the drinks have a diuretic preventing key
hormones from functioning and allowing the kidneys to become dehydrated. Your craving comes from
signals with in the kidney to the brain alerting it to the dehydrated state of your kidneys. As you drink
more water your kidneys use those water molecules and osmosis to filter out the waste products in the
other drinks, resulting your needing to urinate often. The kidneys do this to maintain equilibrium of
molecules in the blood.
Digestion also requires diffusion. As your food moves through the large and small intestine various
enzymes and acids break it down. Like the kidneys it filters the waste from the beneficial. All beneficial
nutrients are absorbed into the blood stream and all waste is defecated. All organs diffuse nutrients
into the blood to be transported throughout the body, however, blood also uses diffusion to maintain its
own PH balance. Blood is slightly acidic and must maintain PH. Many seemingly small issues in the body
are the result of imbalance in the blood. Alkalosis and acidosis are the most common issue regarding
irregular blood PH. Too much of certain acids or bases in the body can slow gas exchange. Carbonic acid,
often used when giving a person anesthesia, will cause the blood’s PH to decrease becoming more acidic
halting O2 production allowing for more carbon dioxide to be produce than oxygen is. However, your
lungs rely on carbonic acid to deliver CO2 from the bloodstream to be then exhaled. If CO2 increases in
the bloodstream the blood will then become to acidic leading to Acidosis, a disorder that affects all vital
organs casing to fail. Diffusion is a major part of the body’s everyday functions and this experiment takes
a closer look at diffusion and what factors affect the rate or ability of molecules to diffuse through a
semi-permeable membrane.
Methods
Hypothesis: If a macromolecule is able to pass through the semi-permeable membrane then the size of
the macromolecule and rate of diffusion can be determined.
Two diffusion experiments were completed simultaneously; the first to observe the diffusion of starch,
and simple sugar and the second to determine the rate of diffusion for starch depending on the weight.
For the first experiment, a 6 centimeter portion of dialysis tube with one tied off end was presoaked in
water prior to beginning the experiment. After the tube was fully soaked it was removed from the
water. After clipping one side 2 millimeters of the starch test solution was put inside the bag. The open
end of the bag was then secured with a second clip. The dialysis bag was placed into a 400 millimeter
(mL) beaker with just enough water for the bag to be fully submerged. The dialysis bag or tube was set
aside to soak for 45 minutes. While the dialysis bag was soaking, the second experiment was started.
After 45 minutes the dialysis tubing was removed from the 400mL beaker. Using a pipette, roughly 10mL
of the remaining solution within the 400mL beaker was transferred to two test-tubes labeled for the
macromolecule test solution, starch or simple sugar. The solution within the test tubes was then tested
using the chemical reagent KMnO4 for starch and Iodine for simple sugar. The sample solution was test
with potassium permanganate KMnO4 reagent by adding 2 drops of KMnO4 to the test tube and heating
the test tube for 5 minutes in a beaker of boiling water.
The second experiment focused on Starch. A new dialysis bag was filled with 2mL starch test solution
and then weighed. The bag was then submerged in water in a 300mL beaker and left to soak for 15
minutes. After the timer went off the bag was removed from the 300mL water beaker and gently patted
dry and weighed again. Using a new pipette, a sample of the solution in the beaker was transferred to
one test tube and tested using the chemical reagent for KMnO4. The dialysis bag was then place back
into the 300mL beaker. These steps were completed again twice more at the 30 minute mark and 45
minute mark recording the weight and the test results.
Results
In the first experiment, the Iodine chemical reagent test for starch was negative for diffusion. The
sample solution with in the test tube was a light golden amber indicating there were no traces of starch.
These findings were on similar with the negative deionized water control. The potassium permanganate
chemical reagent test for simple sugar was negative for diffusion. The sample solution with in the test
tube remained a vibrant magenta color with no precipitate present. The same results were found in the
negative control using deionized water. In the second experiment, the start weight of the 2mL of test
solution within the dialysis tube was 8.6grams and tested negative for starch using the Iodine chemical
reagent. After the first 15 minutes of soaking the dialysis tube maintained a weight of 8.6 grams and
continued to test negative for starch. The second 15 minute test or 30 minute mark test the dialysis bag
gained 8.7 grams but still remained negative for starch. The last 15 minute test results were the same as
the 30 minute mark test weighing 8.7 grams and testing negative for starch.
Discussion
From the results of the second experiment at the 30 and 45 minute mark it can be concluded that the
dialysis bag underwent osmosis instead of the macromolecules diffusing out. These results were
unexpected. From continued research on the sizes of macromolecules, starch is approximately 200kDa
(kilo Daltons) much larger than sugar at 55kDa. It could be deduced that the starch macromolecule was
too large to diffuse in the given 45 minute time frame, however since sugar is a significantly smaller
macromolecule, the test for the first experiment should have reflected some change. Being that there
were no significant changes in the test solutions results are inconclusive and the hypothesis are
inconclusive and cannot be confirmed until further experimental trials at longer time intervals can be
completed.
Sources
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Markings, Samuel(2018 April 25) Examples of Diffusion in Organs
https://sciencing.com/examples-diffusion-organs-22941.html.
Rice University OpenStax. Anatomy and Physiology Chapter 22.4 Gas Exchange
https://opentextbc.ca/anatomyandphysiology/chapter/22-4-gas-exchange/