Osmosis Laboratory Report
Jonathan Paul Loomis
September 27, 1998
09.100.02 Great Experiments in Biology
TA: Heather Emmitte
Introduction
Overview
Our second laboratory project involved a study of the osmosis process. The osmosis process is especially important to us as students of Biology because of its tremendously important role in the workings of the cell. Almost all cellular functions are supported by osmosis.
Purpose
The purpose of this laboratory project was to further our understanding of the osmosis process and how that said process affects the workings of cells, especially in regards to hypertonic and hypotonic solutions.
Hypothesis
My predictions were that the sheep red blood cells (called RBC's hereafter) would swell and appear round like balloons when placed in the NaCl solution because it was a hypotonic solution and the salt from the water would flow into the cells. When placed in the H2O I predicted that the cells would shrink and wither because the chemicals within the cells would flow out into the water that was pure and free of such materials.
I predicted that the solutions with the lowest NaCl content would appear the most clear when mixed in the centrifuge with the RBC. I chose this hypothesis because I believed that the NaCl would cause the hemoglobin from the RBC's would to flow out of the cells and discolor the solution. Therefore, the higher the concentration, the darker the solution would be.
Procedure
The following is a list of materials used in this lab:
The procedures used in this lab are identical to those laid out in the Osmosis Lab Procedure handout given to us on the day of the lab, with the following exceptions: A.5, we did not keep this slide; B.1, we placed the H2O directly onto the slide instead of having seep in from the side; C.2, we allowed the 2% NaCl to permeate in from the side of the cover slip; D.1, not all of out test tubes contained exactly 1 ml of solution; D.9, we drew our graphs with the X and Y axis reversed from what is listed in the handout.
Results
View of sheep's RBC's magnified 400 times
The cells were seen to be light gray and spotted (1). There were also regions of the cells that appeared as a darker gray than the rest of the cell (2).
View of sheep's RBC's in hypotonic solution (distilled H2O) magnified 400 times
These cells appeared as many small dots moving slowly. They were mostly blue due to the dye that was added, but some appeared as aqua or light green in varying shades. Their shape was generally rounded, but not bloated.
View of sheep RBC's in hypertonic solution (2% NaCl) magnified 400 times
These cells appeared light lime color, or pale green. They appeared crumpled (1), however some were still well formed (2).
Color and size of each pellet in the centrifuge tubes
|
Solution |
Color of solution |
Drawing |
Description of pellet |
|
H2O |
Light pink |
|
Large and dark red |
|
0.3% NaCl |
Light pink |
|
Almost none |
|
0.5% NaCl |
Light pink |
|
Very small and light colored |
|
0.6% NaCl |
Lighter pink |
|
Light red |
|
0.7% NaCl |
Clear |
|
Dark red |
|
0.8% NaCl |
Clear |
|
Dark red and large |
|
0.9% NaCl |
Clear |
|
Dark red and fairly large |
|
Unknown % NaCl |
Light pink or peach |
|
Semi-dark red and medium sized |
Individual Absorbance Readings
|
NaCl Concentration |
Absorbance |
|
0.0% (H2O) |
1.4 |
|
0.3% |
1.25 |
|
0.5% |
1.5 |
|
0.6% |
0.8 |
|
0.7% |
0.038 |
|
0.8% |
0.030 |
|
0.9% |
0.005 |
|
Unknown Z |
0.75 |
Group Absorbance Averages
|
NaCl Concentration |
Absorbance |
|
0.0% (H2O) |
1.42 |
|
0.3% |
1.18 |
|
0.5% |
0.93 |
|
0.6% |
0.54 |
|
0.7% |
0.10 |
|
0.8% |
0.06 |
|
0.9% |
0.03 |
|
Unknown Z |
0.56 |
|
Unknown X |
0.07 |
|
Unknown Y |
1.20 |
Discussion
This lab demonstrated clearly to me that my initial hypothesis was incorrect. The effect the hyper and hypotonic solutions had on the RBC's was the exact opposite from what I had initially predicted. Whereas I had predicted that the H2O would shrink the cells, it instead enlarged them, as the water molecules moved into the cells by osmosis filling the area inside the cell membranes that did not have any water in them. In like form, whereas I had predicted that the cells would take on the NaCl solution, they did the opposite and expelled their hemoglobin and collapsed, leaving crumpled shells behind. While the results do not support my predictions, I also question whether or not they are in themselves correct. I would like to do further experiments to determine if the hemoglobin escaped from the cells due to the fact that there was no hemoglobin outside the cells and it therefore moved by osmosis to counteract this imbalance or if the NaCl moved into the cells due to an imbalance of NaCl and the cells exploded, thus releasing the hemoglobin.
Because the experiment demonstrated that more hemoglobin was released into the solution that surrounded the cells when the percent NaCl was lowest, this leads me to believe that there may be some correlation between the percent NaCl content of the solution, and the percent NaCl that the cells themselves contain. I do not feel as though I have enough evidence to draw any definite conclusions at this point concerning the osmosis process.
The conclusions I can draw are that the Unknown solution Z was most likely 0.6% NaCl, Unknown X was most likely 0.8% NaCl, and Unknown Y was most likely 0.3% NaCl.
There are many possible things that could have gone wrong with this experiment that might have altered my results. In section A, I believe I read a large group of cells to be a single cell with individual parts due to poor focusing of the light microscope. In section D, my partner and I did not zero out the absorbance meter for some of our measurements which might have thrown them off, and it is possible that imperfections in pouring the solutions from the centrifuge tubes into the test tube may have altered the solution makeup. It is further possible that the test tubes were not cleaned fully before being placed into the spectrophotometer and therefore would not be read correctly.
