Introduction
Diffusion is the movement of particles from an area of higher concentration to lower concentration. The overall effect is to equalize concentration throughout the medium. Examples of diffusion include perfume filling a whole room and the movement of small molecules across a cell membrane. One of the simplest demonstrations of diffusion is adding a drop of food coloring to water.
Osmosis is the passive transport of a solvent and in the human body, the solvent is water (McLafferty, Johnstone, Hendry & Farley, 2014). Diffusion and osmosis are both types of passive transports, meaning that they do not require energy, since they are going from an area of high concentration to low concentration.
A cell’s outer layer is a plasma membrane, which is made out of a phospholipid bilayer. This plasma membrane has selective permeability, meaning it only allows certain things to pass through it. In the case of water, it is transported into a cell using facilitated diffusion, which means that a protein carries the substance into the cell. A protein that is used to facilitate water passage through the plasma membrane is called aquaporin. A protein is needed to allow the water into the cell due to the phospholipid bilayer of the plasma membrane. The outer layer of the membrane hydrophilic, or likes water, and the inner layer of the membrane is hydrophobic, or dislikes water. This keeps the water from being able to transport through the plasma membrane on its own without the facilitation of protein channels.
Osmosis is the movement of solvent particles across a semipermeable membrane from a dilute solution into a concentrated solution. The solvent moves to dilute the concentrated solution and equalize the concentration on both sides of the membrane.
Osmosis occurs in the body in order for the cell to maintain water balance. Examples of osmosis include red blood cells swelling up when exposed to fresh water and plant root hairs taking up water. To see an easy demonstration of osmosis, soak gummy candies in water. The gel of the candies acts as a semipermeable membrane.
The experiment aims to look at osmosis by determining how blood cells’ shape and size change, or do not change, in reaction to different concentrations of Sodium Chloride (NaCl). Red blood cells will be used to look at how osmosis plays a part in animals’, including humans’, bodies. In this experiment the independent variable will be treatment of the red blood cells with a solution and the dependent variable is the size and shape of the cells. The control is the treatment of sheep blood with sheep blood plasma.
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The tonicity of these solutions will determine what the change in cell shape and size will be. In hypotonic solutions there is a higher level of solute inside the cell, so water moves into the cell. In hypertonic solutions, the solute concentration is lower inside of the cell than outside so water moves outside of the cell. An isotonic solution will allow the amount of water and solute to remain the same both inside and outside of the cell. In the case of red blood cells, a 0.9% Sodium Chloride solution is considered an isotonic solution.
Objective
To determine how blood cells’ shape and size change, or do not change, in reaction to increases in concentration of Sodium Chloride (NaCl).
Hypotheses
If blood plasma is mixed with the red blood cells, then there will be no change in cell size.
If distilled water (0% NaCl) is hypotonic, then the size of the cell will increase when the solution is added.
If normal saline (0.9% NaCl) is isotonic, then there will be no change in cell size, so the cells will look the same as before the solution is added.
If 10% NaCl is hypertonic, then the cells will crenate when the solution is added.
Materials/Procedure
Procedure
A drop of sheep’s blood was treated with either one drop of distilled water, 0% NaCl; normal saline, 0.9% NaCl; or 10% NaCl. Each was mixture was mixed together using a slide cover. The slide cover was then placed on top of the solution. The slide cover was applied on the samples and the samples were viewed under a light microscope at 400X magnification to observe the shape and size differences in the sheep’s blood cells.
Results
In the control,when the sheep’s blood was treated with a solution of sheep’s blood, there was no observed change in cell shape or size when viewed under the microscope. When the treatment of distilled water (H2O with 0% NaCl) was added to the sheep’s blood, there was only one cell when viewed under the microscope. When the treatment of normal saline (H2O with 0.9% NaCl) was added to the sheep’s blood, there was no observable change in the shape or size of the sheep’s red blood cells When the treatment of H2O with 10% NaCl was added to the sheep’s blood, the blood cells appeared to crenate, which means that the cells shrunk and had scalloped edges, when viewed under the microscope
Figure 1 (below) is a table of the independent variable, solution treatments, and the dependent variable, observed cell size and change in relation to red blood cell shape and size before solution was added.
Treatment
Observed Change in Cell Size and Shape
Sheeps Blood
No observable change in cell shape or size
Distilled water (H2O with 0% NaCl)
One cell observed (Hypotonic)
Normal saline (H2O with 0.9% NaCl)
No observable change in cell shape or size (Isotonic)
H2O with 10% NaCl
Cell shrinkage with scalloped edges (crenation) observed (Hypertonic)
Figure 1. Treatment and Observable Cell Changes
Discussion
The goal of this experiment was to determine how blood cells’ shape and size change, or do not change, in reaction to different concentrations of Sodium Chloride (NaCl). This was tested in the laboratory using sheep blood cells and observing how the cells changed size and shape with treatments of varying tonicity. Water, the solvent, moves to where the higher concentration of solute, NaCl, so water is what is moving in or out of the cell based on the tonicity of the solution (McLaffery et al., 2014).
The first hypothesis states that if plasma is mixed with the red blood cells, then there will be no change in cell size, so the cells will look the same. When viewed under the microscope, there was no observable change in cell size or shape. This supports that plasma will not change the shape or size of the red blood cells and supports that the blood plasma is an isotonic solution, allowing water to enter and exit the cell at the same rate.
Another hypothesis tested was that if distilled water (0% NaCl) is hypotonic, then the size of the cell will increase when the solution is added. When viewed under the microscope after the solution was put on the red blood cells, there were no cells seen. This supports the hypothesis that the distilled water is a hypotonic solution, allowing more water to enter the cell than exit the cell and eventually the cell lysed, or burst. An improvement to the experiment would be to look at the cells under microscope as solution is added to see the hypotonic solution cells lyse. Without seeing this change in the red blood cell happen, the conclusion is deducted but not observed.
The hypothesis that, if normal saline (0.9% NaCl) is isotonic, then there will be no change in cell size, so the cells will look the same as before the solution is added, was supported. When the normal saline was added to the red blood cells there was no observable difference in cell shape or size. This supports that normal saline is an isotonic solution, meaning that the concentration of water was equal both inside and outside of the cell.
The final hypothesis states that if 10% NaCl is hypertonic, then the cells will crenate when the solution is added. This hypothesis was supported when cell crenation was observed when the sheep blood cells were viewed under the microscope. The cell crenation supports that a solution of 10% NaCl is a hypertonic solution, meaning that more water exited the cell than entered, causing the cell to shrink.
Clinical significance
Cerebral edema is the swelling of the brain. It can be caused as a result of different issues such as ischemic stroke, brain tumor, intracerebral hemorrhage, meningitis, encephalitis, tuberculosis, poisoning, hyponatremia, or opioid abuse (Jha, 2003). In cerebral edema, glutamate is released, triggering the opening of Calcium and Sodium channels in the cell membrane to open, which allows the Calcium and Sodium into the cell (Jha, 2003). The amount of Sodium in the cell builds up and since water moves to the area of higher solute concentration, water then enters the cell, causing it to swell (Jha, 2003).
It has been found that using hypertonic solutions, such as Glycerol, which is a 2.5% saline solution, are helpful in treating cerebral edema because it encourages water to move from out of the brain into the blood (McLafferty et al., 2014). Mannitol, which can come in varying concentrations, is another hypertonic solution used for the treatment of cerebral edema (Jha, 2003).Mannitol has been found to have more negative side effects, such as electrolyte imbalance, and needs to be monitored closely (Jha, 2003).
References
Jha, S. (2003). Cerebral Edema and its Management. Medical Journal, Armed Forces India, 59(4), 326–331. http://doi.org/10.1016/S0377-1237(03)80147-8
McLafferty, E., Johnstone, C., Hendry, C., & Farley, A. (2014).
Sheeps Blood (Nothing Added)
(Distilled Water)
Normal saline (H2O with 0.9% NaCl)
H2O with 10% NaCl
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