Lab Report #1 - Membrane Transport: a Simulation of Diffusion Using Dialysis Tubing PDF

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Membrane Transport: a Simulation of Diffusion Using Dialysis Tubing...

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Lab Report #1 Membrane Transport: a Simulation of Diffusion Using Dialysis Tubing PHYL 141 Lab, Section 001 Monday!

Abstract "

Osmosis is a process which results in the equalizing of the concentrations on each side

of a semipermeable membrane. The rate of diffusion is influenced by many factors such as the temperature of the environment, the mass of the solute, and the solvent density. It is hypothesized that each solution is going to reach dynamic equilibrium but when they do it is dependent on the solution concentration and particle size that will ultimately influence the rate of diffusion. Our group believes that the smaller the particle size and the higher the concentration, the higher the rate of diffusion across a membrane will be. To test this hypothesis, 4 different solutions were put into dialysis tubing and left to sit in a beaker filled with water for intervals of 15 minutes for a total of 60 minutes. After each interval, the tubing was dried and then weighed to collect the data for that specific solution. The results of the experiments show that the rate of osmosis was higher in solutions with higher concentrations. This was demonstrated by the solutions absorbing the most water from the greatest to the least: 4M glucose, 2M glucose, 2M NaCl, and H2O. Because of this, our hypothesis was supported by our results. Further improvements can be made by making sure each time the dialysis tube is taken out that it is fully dry by letting it dry longer or finding a more effective way of drying the tubing before it is weighed to assure there is the least amount of error possible that may interfere with the results.!

Introduction In other words, osmosis is the diffusion of water. This occurs by molecules of a solvent passing through the membrane from a less concentrated solution into a more concentrated one. As soon as dynamic equilibrium is achieved the rate of diffusion plateaus. In Marieb and Smith’s Human Anatomy and Physiology Laboratory Manual they define dynamic equilibrium as “a state when concentrations of particles on both sides of a membrane are at equivalent levels” (46). However, this does not mean the particles have completely stopped moving, “Particles are still moving across the membrane, but this movement causes no net change in concentration” (46). Several factors determine the rate of particle diffusion across semipermeable membrane. The factors are concentration, size, temperature, surface area, and polarity. In this experiment, we used 4 different solutions: H2O, 2M glucose, 4M glucose, and 2M NaCl to measure this with dialysis tubing to simulate a plasma membrane. As a group, we hypothesized that the smaller the particle size and the higher the concentration, the higher the rate of diffusion across a membrane will be. We concluded this because when it comes to the rate of particle diffusion, size and concentration play a huge role in the process. “Small size particles will have a greater rate of diffusion because they encounter less resistance” (44), this means that smaller particles will not only spread out but also permeate membrane much faster than larger particles. As for concentration is an important factor because “greater the difference of concentration on either side of the membrane, the greater the rate of diffusion” (44).

Materials and Methods • 8-10 inch strip of dialysis tubing! • 2M and 4M glucose solutions ! • 2M NaCl solution ! • 1ml pipette and tips! • beakers! • paper towels! • balance! "

There were several groups each assigned with 1 out the 4 different solutions. Our

specific group was assigned H2O. First, we put 2ml of H2O in the dialysis tubing and tied knots on both ends. We then weighed the tubing and recorded its starting weight. Next we placed the tubing into the beaker with water and timed it for 15 minutes. After the 15 minutes were up we removed the tubing from the beaker and dried it off thoroughly before weighing it. We repeated this same step for 3 more intervals of 15 minutes and recorded the weight after every time. The other groups followed this exact same method only with a different solution. Together our recorded measurements created a table of data. !

Results Table 1: Weight measurements were obtained every 15 minutes for a total of 60 minutes. These are the results of the experiment for the 4 different solutions. !

Membrane Dialysis Experiment Data Time

Groups

2M Glucose

0 minutes

Group 1

2.850

2.750

2.909

Group 2

3.001

2.913

2.863

Mean

2.926

2.832

Group 1

3.895

3.861

3.332

Group 2

3.728

3.909

3.212

Mean

3.812

3.885

Group 1

4.483

4.753

3.357

Group 2

4.178

4.648

3.227

Mean

4.331

4.701

Group 1

4.919

5.342

3.404

Group 2

4.646

5.161

3.274

Mean

4.783

5.252

Group 1

5.188

5.730

3.422

Group 2

4.987

5.577

3.316

Mean

5.088

5.654

15 minutes

30 minutes

45 minutes

60 minutes

4M Glucose 2M NaCl

H2O

2.836

2.636 2.646

2.769

2.641

3.282

2.845 2.684

3.275

2.765

3.395

2.939 2.637

3.326

2.788

3.359

2.785 2.658

3.346

2.722

3.341

2.776 2.634

3.360

2.705

Effects of Concentration 6

4.919

5

5.188 4.987

4.646 4.483 4.178 3.895 3.728

Weight of Tubing (g)

4

3

3.001 2.85 1M Glucose 2M Glucose

2

1

0 1

2

3

4

5

Time Elapsed (minutes)

!

Figure 1: Comparing data for 1M glucose versus 2M glucose solutions. This line graph shows the effects of concentration on the rate of diffusion. In this graph although they are the same solution 2M has a higher concentration which is the reason why it has a higher rate of diffusion.!

Effects of Particle Size 6

5.088 5

4.783 4.331

Weight of Tubing (g)

4

3.812

3.275 3

3.326

3.346

3.36

2.926 2.769

2M Glucose 2M NaCl

2

1

0 1

2

3

4

5

Time Elapsed (minutes)

Figure 2: Comparing 2M glucose versus 2M NaCl solutions. This line graph shows the effects of particle size on the rate of diffusion. In this comparison, glucose has smaller particles than NaCl resulting in glucose having a much higher rate of diffusion.!

Discussion "

The results of the experiment show that each solution has a different rate of diffusion

because of factors such as solution concentrations and particle sizes. The smaller the particle size and the higher the concentration, the higher the rate of diffusion across a membrane will be. Because of these results, our hypothesis ended up being correct. Our group expected these results by taking into consideration the factors that affect a solution’s rate of diffusion such as concentration, size, temperature, surface area, and polarity. These factors all together have the potential to be beneficial or detrimental to osmosis or diffusion occurring. This lab demonstrated exactly this by helping visualize just how important this process is to us. In Membrane Transport Proteins, Pardee discusses just this. The membrane is an essential part to this process because it “constitutes a barrier to nutrients being brought in and waste products being excreted. However, transport systems are built into membranes in a way that provides for selective permeability. By this process, only necessary materials are transported” (632). Although in this case, the plasma membrane was being simulated by dialysis tubing it still demonstrated molecules passing though the membrane from various concentrations. Odom in Secondary & College Biology Students' Misconceptions about Diffusion & Osmosis also discusses the importance of understanding both osmosis and diffusion. As for they are vital to understanding several important life processes, “diffusion is the primary method of short distance transport in a cell and cellular systems” (409) and “osmosis is key to understanding…transport in living organisms” (409). Both of these concepts are closely related and can be tied into not just human anatomy and physiology but also biology, physics, and chemistry. This lab is valuable in many ways but mostly because it can be applied to real world scenarios such as the osmosis occurring in kidney dialysis or the diffusion occurring when gas is being exchanged in the lungs or during movement of oxygen in the blood.!

References Arthur Louis Odom. (1995). Secondary & College Biology Students' Misconceptions about Diffusion & Osmosis. The American Biology Teacher, 57(7), 409-415. doi: 10.2307/4450030!

Marieb, E., & Smith, L. (2016). Diffusion Across Biological Membranes: A simulation using! Dialysis Tubing. In Human Anatomy and Physiology Laboratory Manual (12th ed., pp. 61-63). New York, New York: Person Learning Solution.!

Pardee, A. (1968). Membrane Transport Proteins. Science, 162(3854), 632-637. Retrieved from http://www.jstor.org/stable/1725415...