Osmosis and Diffusion
The basic principles of Osmosis and Diffusion were tested and examined in this lab. We examined the percent increase of mass and molarity of different concentrations of sucrose in the dialysis bag emerged in distilled water and the potato cores emerged in concentrations of sucrose. The data reinforces the principles of Osmosis and Diffusion, and in a biological context, we can simulate how water and particles move in and out of our own cells. Introduction
1. Investigate the process of osmosis and diffusion in a model of a membrane system.
2. Investigate the effect of solute concentration on water potential as it relates to living plant tissue. Background Information:
Molecules are in constant motion; they tend to move from areas of high concentration, to areas of low concentration. This broad principle is divided into two categories: diffusion and osmosis. Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. This is considered a passive form of transportation because it does not require any additional energy to transport the molecules. In the body, carbon dioxide and oxygen can diffuse across cell membranes.
Osmosis is a special type of diffusion where water moves through a selectively permeable membrane from a region of higher water potential to a region of lower water potential. In our body, water diffuses across cell membranes through osmosis. Water potential is the measure of free energy of water in a solution and is shown with the use of the symbol Ψ. Water potential is affected by two factors: osmotic potential (Ψπ) and pressure potential (Ψp). Osmotic potential is dependent on the solute concentration, and pressure potential which is the energy that forms from exertion of pressure either positive or negative on a solution. The equation to find the sum of water potential is: Water Potential = Pressure Potential + Osmotic Potential
Ψw = Ψp + Ψπ
The purpose of this lab is to observe the physical effects of osmosis and diffusion and to determine if it actually takes place. We hypothesize that, because molecules diffuse down a concentration gradient, the mass of the dialysis tubes will increase, and we believe that as the molarity increases, the percent of change in mass will also increase. Hypothesis:
Diffusion and osmosis will occur until dynamic equilibrium is reached. As the sucrose concentration of the solution increases so will the mass. Materials
1. 6 strips of dialysis tubing
2. Distilled water 15-20ml
3. 0.4 M sucrose 15-20ml
4. 0.8 M sucrose 15-20ml
5. 0.2 M sucrose 15-20ml
6. 0.6 M sucrose 15-20ml
7. 1.0 M sucrose 15-20ml
8. 6 Beakers
1. 100ml of distilled water
2. 100ml of 0.4 M sucrose
3. 100ml of 0.8 M sucrose
4. 100ml of 0.2 M sucrose
5. 100ml of 0.6 M sucrose
6. 100ml of 1.0 M sucrose
7. 6 Beakers
8. Potato slices (4 for each solution)
10. Plastic wrap
1. Obtain 6 strips of dialysis tubing and tie a knot in one end of each. 2.
Pour approximately 15-20ml of each of the following solutions into separate bags. 3. Remove most of the air from the bag and tie the baggie.
4. Rinse the baggie carefully in distilled water to remove any sucrose that may have spilled and carefully blot.
5. Record the mass of each baggie and record.
6. Fill six 250ml beakers 2/3 full with distilled water and place a bag in each of them. Make sure that you record which baggie is which.
7. Let the bag sit for 20-30 minutes.
8. After 20-30 minutes, remove baggies from the water, and carefully blot dry.
9. Measure the mass of each baggie and record.
1. Pour 100ml of your assigned solution into a beaker. Slice a potato into 4 equal lengths about the shape of French fries or tubes. 2. Determine the mass of the 4 potato cylinders together and record. 3. Place the cylinders into the beaker with your assigned solutions and cover with plastic wrap. Leave overnight. 4. Remove the cylinders from the beakers and carefully dry them. Record the room temperature in Celsius. 5. Determine the mass of the 4 potato cylinders together and record.
From these results, it can be concluded that the hypothesis is justified and correct. The data shows that the mass increased as the concentration of the sucrose solution increased. Osmosis is clearly being replicated in the physical form. Analysis
Change in mass depends on the concentration of sucrose within the dialysis bags. If the concentration of sucrose is greater inside the bag than outside, then water will move into the bag. If the concentration of sucrose is lower inside the bag than outside, then water will move out of the bag. These two things are directly proportional. As the mass increases, so does the molarity. These are inversely proportional because whenever the sucrose molarity inside the bag is more concentrated, it will become more dilute and vise versa. The solutions will reach equilibrium somewhere between the two concentrations.
The hypothesis is accepted based on the data that was obtained because as the sucrose concentration increased so did the final mass of the solutions. One possible source of error could be the tightness of the string that tied off the dialysis tubing. If there was a leak or a break in the dialysis tubing, all of the data would be off. Another possible source of error could be that the students did not pat dry the potato sample well enough causing drops to be left on the electronic balance, tarring it incorrectly, causing all other data to be off slightly. Simple mathematical errors always occur, so there is always room for simple algebraic mistakes in this section of the lab.
The purpose of this lab was to describe the physical mechanism of osmosis and diffusion and describe how molar concentration affects diffusion. We have now observed how solutions diffuse in different situations, always from a high concentration to a low concentration, and how molar concentration affect diffusion, as the molarity goes up, more solution is diffused. We hypothesized that because molecules diffuse down a concentration gradient, the mass of the dialysis tubes will increase, and also that as the molarity increases, the percent of change in mass will also increase. Our data did support our conclusion.
Exercise 1 proved that water moves across the selectively permeable membrane of the dialysis tubing much easier than sucrose sugar does. The water moved to reach equilibrium between the solutions. Sucrose must be too large a molecule to pass through the membrane quickly. Exercise 2 showed that the potato samples took in water when immersed in a distilled water solution. Potatoes must contain sucrose molecules due to the conclusion of this lab because the potatoes take in water in the distilled water beaker. Potatoes had a lower water potential and higher solute potential than the distilled water. It is just the opposite inside the beaker.
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