Osmosis and Iodine Lab Report 1

Osmosis and Iodine Lab Report

Introduction
 Osmosis and Iodine Lab Report 2

Osmosis has two different forms of transportation. These two forms of transportation are

passive transport and active transport. This lab focuses on passive transport, the movement of

particles move from a high concentration to a low concentration across a cell membrane that

does not require ATP or excess energy to perform this function. The dialysis tubing being used

in the lab simulates the cell membrane of a cell. The cell membrane simulated in this lab is

selectively permeable, meaning certain particles of certain substances are allowed to pass

through. This was shown the in students lab with the Iodine and starch, as one substance was

able to move through the dialysis tubing, while the other could not. Osmosis is the movement of

water going from the lower concentration to a higher concentration that helps reach equilibrium

between the concentrated solution and water (Gemma, 2014). If there is more water inside the

cell than outside, then the hypertonic environment over time will reach an isotonic environment

because the water moves in and out of the cell membrane. This same process is repeated within

hypotonic environments as well. Osmosis is very common and important when studying cells

(Yaroshchuk, 2017). There are three different osmotic environments a cell could be in. The cell

could be in a hypotonic environment, which is when the concentration of water is higher outside

the cell than inside. A cell could also be in a hypertonic environment, which is when the

concentration of water is lower outside the cell than inside. However, all cells want to reach

equilibrium, which is at the third environment. An isotonic environment is when the

concentration of water is equal outside and inside the cell. When a hypotonic cell undergoes

osmosis to reach equilibrium, it could possibly burst because of too much water rushing into the

cell. A hypertonic cell experiences a similar thing, as when it undergoes osmosis to reach

equilibrium, it could shrivel up because there is not enough water still in the cell. Osmosis

impacts people in everyday life, and knowing osmosis while a person goes bat their day could
 Osmosis and Iodine Lab Report 3

save their life possibly. If a person has too much water in their bodies, they run the risk of

having their cell burst, which could kill them because they have placed their cells in a hypotonic

environment. The purpose of doing this lab was to see how difference in concentration gradients

affect the rate of osmosis, how time affects the rate of osmosis as you reach equilibrium for the

first part of the lab, and what was permeable to the dialysis tubing. A concentration gradient is

where there is a high water concentration in an area while the other area has a low concentration

gradient (BBC, 2014). In order to set up part one of the lab, four beakers were filled with 200

milliliters of water, and each beaker had a different concentration of glucose. One beaker has

20%, another had 40%, and the last had 60%. One beaker filled with water had a bag of pure

water, and the last beaker was 80% starch and a bag with 60% starch as well as a bag of pure

water. Part two was set up by filling a bag with starch, and dropping Iodine into the water and

letting it sit for 15 minutes. The dependent variable in the first part of the lab was the dialysis

tubing’s mass, and for part two was the color change. The independent variable in part one was

the amount of glucose in the solution, or osmotic environment. The independent variable for

part two of the lab was where the starch was placed, with the starch being inside the bag and not

outside the bag. The constants for part one consisted of the 5mL of solution per dialysis tubing,

the 200mL solution amount per beaker, how the dialysis tubing was tied, the time intervals, when

all the dialysis tubings were taken out and placed back into the beakers at the same time, and

drying off the dialysis tubing before weighing in at each interval. The control group for part one

was the beaker with water and the dialysis tubing with water inside of it. The other beakers are

apart of the experimental group, with varying amount of glucose in each, some hypotonic

environments for the dialysis tubing, while others are hypertonic. The constants for the second

potion of the lab were 20 drops of Iodine, 1/2 spoon of starch solution, and rinsed off dialysis
 Osmosis and Iodine Lab Report 4

tubing before being placed into the beaker. The control group for this part of the lab was the

before stage of the beaker and dialysis tubing, with yellow water in the beaker with white starch

in dialysis tubing. The experimental group was the after stage, clearer water with a dark blackish

bluish purple color inside dialysis tubing. In part one, if you put a bag with a higher

concentration of glucose in water, then that leads to a greater change in mass. In part two, if the

iodine is dropped into the beaker of water with a bag filled with starch, then the iodine will move

into the bag and end up coloring the starch.

Materials

- 6 beakers

- 7 dialysis tubing bags

- 20 drops of Iodine

- Scale

- Paper towels

- Starch solution, 20%, 40%, 60%, and 80%

- Water

- Stopwatch

- Graduated cylinder

- 6 pipettes

- 14 pieces of string

Procedure

Part 1
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1. Take 6 dialysis tubing bags from their bin where they are being soaked, and fold the one end

in 1 centimeter. Then tie a string around the end securely. Finally cut off loose remaining string.

2. Fill the bags with different percentages of starch. Bag 1 gets 1/2 filled with tap water. Bag 2

gets 1/2 filled with 20% starch. Bag 3 gets 1/2 filled with 40% starch. Bag 4 gets 1/2 filled with

60% starch. Bag 5 gets 1/2 filled with tap water. Bag 6 gets 1/2 filled with 80% starch.

3. After filling the bags, tie the other end of the bag by folding it 1 centimeter and wrapping

string around it. Then cut the remaining string. In order to remember which bag is which, put a

number on each paper towel, one paper towel per bag.

4. Obtain a glass weighing dish, and separately weigh the bags. Record the mass on a chart.

5. Place the bags in the appropriate beakers.

6. At 3 minutes, 6 minutes, and 9 minutes, take the bags out of the beakers at the same time to

dry them off so they can be weighed to the nearest gram with care. Record the new mass in the

appropriate column and row at each interval. Place the bags back in at the same time, and do not

mix up the bags.

7. Record data from bag 1 into Table 1. For bags 2-6, take the average weights of each and put

those into Table 1.

Part 2

1. Take the dialysis tubing and fold it 1 centimeter and then tie the bag with string. Cut the string

2 centimeters and make additional knots with the remaining string.

2. Take the dialysis tubing and fill 1/2 with starch.

3. Add roughly 1 teaspoon of starch to the dialysis tube. Fold the second end 1 centimeter and

tie it, then cut the string.

4. Take the bags and rinse them cautiously with water to rinse of any starch from the sides of the

bag that could obstruct with the data. Dry the bag by patting it lightly and set it to the side.

5. Fill the beaker halfway with tap water and add 20 drops of Iodine. Place the cell into the

water with the iodine drops. Fill out the chart with the starting color in the cell and color of the

iodine water.

6. After 15 minutes remove the cell and pat dry.

7. Take note of color changes within the beaker. Fill out the changes in the chart about the color

change.

All Procedure information found in Diffusion Through Cell Membrane packet.

Results

Table 1

Mass Changes of Simulated Cells versus Time

Time Water in 20 % in 40% in 60% in Water in 80% in 60%

0 0 0 0 0 0 0

3 0.208 0.317 0.408 0.567 -0.15 0.241

6 0.291 0.534 0.8 1.009 -0.533 0.316

9 0.249 0.701 1.108 1.409 -0.783 0.399

Description: The data describes the mass change at each interval. The mass change at zero
minutes is 0. The chart shows that the higher percent of starch means the change in mass is
larger than the bags with the lower percent of starch. The 20% bag increased steadily to 0.701g
after 9 minutes. The 40% bag increased steadily to 1.108g after 9 minutes. The 60% bag
increased steadily to 1.409g after 9 minutes. The Water bag in 60% starch decreased steadily
over 9 minutes to -0.783g. The 80% bag in 60% starch steadily increased to 0.399g after 9
minutes. The bags that gained mass at each interval are placed into a hypotonic environment,
and the bag that loses mass is in a hypertonic environment. The water in water already is in an
isotonic environment.

Figure 1
 Osmosis and Iodine Lab Report 7

Mass of the Bags (in grams) vs Time

1.8

1.2
Water in Water
Mass of bags 0.6 20% in Water
40% in Water
(in grams) 60% in Water
0 Water in 60%
80% in 60%
-0.6

-1.2
0 minutes 3 minutes 6 minutes 9 minutes

Description: The data in the graph shows the different concentration gradients of starch in the
water. At each time interval, the new mass change is recorded. The hypertonic environment
series decreases in mass at each interval. All the hypotonic environment series increase at each
interval. The water in water series goes up, and then down slightly.

Description: In part 2 of the lab, the water went from a yellow, from the iodine drops, to a clearer
color. The starch in the bag went from a white substance to a blackish blue color.

Discussion

As the data shows, the dialysis tubing in hypotonic environments all gained mass as time

progressed. This is because as time goes on, osmosis occurs to reach equilibrium and make the

bag into an isotonic environment. This leads to water entering the bag, which means an increase

in weight. The bags that have more starch solution need more water to reach equilibrium. That is

why the graphs show a steeper line for the higher concentration gradient. The water in water bag

goes up and down, as water at the time intervals could have more or less with water constantly

moving between the bag and the beaker. The hypertonic bag constantly goes down because the

water in the 60% starch beaker is leaving the bag, as the environment inside the bag has to much

water to keep it from equilibrium. In order to become isotonic, the dialysis tubing needs to lose

water, leading to a decrease in mass. As time progresses, the closer the simulated cell gets to
 Osmosis and Iodine Lab Report 8

equilibrium, the change in mass begins to slow down, until it reaches equilibrium. From that

point on the chart will show a steady increase and decrease. This was not able to be shown in

this lab because the times were shortened. Shortening the times was a source of error because

this lead to not showing the progression of data to visualize the rate of osmosis. Another source

of error came from the 80% bag in 60% starch not matching up similarly with 20% in water.

The difference between the two is 20%, so the data should have been roughly the same, not

nearly 0.4g different. This could be because the second water bag shared the beaker with the

80% bag. The bags could have reacted differently, as the water from one bag could have entered

the other bag, trying to speed up the osmosis process of one more than the other. In part 2 of the

lab, the reason the bag changed color is because the bag is permeable to iodine, allowing iodine

to move from the water into the bag and changing the color of the starch. If the iodine was

placed in the bag and the beaker was starch, the iodine would move out of the bag, as starch

cannot pass through the dialysis tubing. A third source of error could have been a mix up with

the weight. While preparing the lab, it is easy to have forgotten to set the scale before the lab

began, which would have offset the data by a set amount. One change that would be made to the

lab would be to increase the interval time to show the data more accurately. Shortening the

intervals not only affected the results, but also led to error. Feeling rushed, the amount of water

in the beakers and/or the bags may have not been at 5 milliliters. The bags may also have not

completely wiped water off the bags, as focusing on getting the data was prioritized over the

quality of the data.

Conclusion

The hypothesis for part 1 was supported because the concentration gradient affects the

change in mass. The hypothesis for part 2 was supported because the bag is only permeable to
 Osmosis and Iodine Lab Report 9

iodine and not starch.The lab about different concentration gradients and showing the semi-

permeable cell membrane simulated through the dialysis tubing all represent what osmosis is and

how fascinating and vital it is to understanding cells. Without the knowledge of osmosis, daily

life would be changed and the study of cells would miss very important information on how they

operate.

Works Cited Page

BBC News (2014). Standard Grade Bitesize Biology - Cells and diffusion : Revision. Retrieved

from http://www.bbc.co.uk/bitesize/standard/biology/investigating_cells/

cells_and_diffusion/revision/1/.

Gemma, Will (2014). 7 Examples of Osmosis in Everyday Life. Udemy Inc.

Yaroshchuk, A. (2017, March 23). "Breakthrough" osmosis and unusually high power densities

in Pressure-Retarded Osmosis in non-ideally semi-permeable supported membranes.

Retrieved from https://www.nature.com/articles/srep45168