Lab Report on Osmosis

Introduction
A computerized simulation experiment will be conducted in order to study the cell transport mechanism via the cell’s selectively permeable membrane and passive processes of simple and facilitated diffusion. The plasma membrane is a gateway which allows nutrients to enter the cell and keep undesirable substances out, hence, making it selectively permeable. One method of transport is called active transport, which uses ATP to transport substances through the membrane. The other is called passive process, which does not require ATP energy and the transport process is driven by concentration or pressure differences between the interior and exterior of the cell. All molecules are in constant motion, ergo, possessing kinetic energy. This kinetic energy is the motivating force in diffusion. During diffusion, molecules that are small enough to pass through a membrane’s pores or molecules that can dissolve in the lipid bilayer of a membrane move from an area of higher concentration to an area of lower concentration. Facilitated diffusion occurs when molecules are too large to pass through a membrane or are lipid insoluble. Thus, in the process, carrier protein molecules located in the membrane combine with solutes and transport them down the concentration gradient. Hypothesis
Activity One: Simple Diffusion- Simulating Dialysis
Simple diffusion will occur between different concentrations until equilibrium is reached.
Activity Two: Simulating Facilitated Diffusion
Facilitated diffusion will occur between different concentrations.
Material and Methods * Two beakers * Membrane holder * Four Dialysis membranes: 20 (MWCO), 50 (MWCO), 100 (MWCO), 200 (MWCO). * Membrane barrier * Four solutes: NaCl, Urea, Albumin, Glucose * Solution dispenser * Deionized Water * Beaker Flush * Timer * Computerized Simulator
Using the computerized simulator, the first step of the first experiment, you must place the 20 (MWCO) dialysis membrane into the membrane holder. The membrane holder is joined between two glass beakers; one on the left, the other to the right. Next, 9.00 (mM) of NaCl concentration is dispensed into the left beaker and deionized water is dispensed in the right beaker. As the timer begins, the barrier that surrounds the membrane holder lowers to allow the contents of each beaker to come into contact with the membrane. After 60 minutes of compressed time elapsed, results were shown and recorded. Final step requires the beakers to be flushed for preparation of the next experiments. The exact steps were followed using each dialysis membrane size 20 (MWCO), 50 (MWCO), 100 (MWCO) and 200 (MWCO); as well as with each solute; NaCl, Urea, Albumin, and Glucose. There were a total of sixteen runs in the experiment.
Activity Two: Simulating Facilitated Diffusion
Material and Methods: * Two glass beakers * Membrane builders * Membrane holders * Solution dispenser * Timer * Glucose concentration * Beaker Flush * Deionized water * Computerized Simulator
Using the computerized simulator for this experiment, the first step is to adjust the glucose carrier to 500 so to correctly build the membrane. Next, the membrane is built in the membrane builder by inserting 500 glucose carrier proteins. Then, the newly built membrane is placed into the membrane holder that joins between the two beakers. 2.00 (mM) of glucose concentration is dispensed into the left beaker and deionized water is filled in the right beaker. After 60 minutes of compressed time, results were shown and recorded. Final step requires the beakers to be flushed for preparation of the next experiments. The exact steps were followed and repeated by increasing the glucose concentration to 8.00. Both the 2.00 (mM) and 8.00 (mM) glucose concentration solution were tested using membranes with 500,700, and 900 glucose carrier proteins. There were a total of six experimental runs.
Results
Activity I- Simple Diffusion (Table 1)
Solutes that diffused into the right beaker are indicated by a +.
Solutes that did not diffuse into the right beaker are indicated by a -.
Membrane (MWCO) Solutes (9.00mM) Pore Size | NaCl | Urea | Albumin | Glucose | 20 | - | - | - | - | 50 | + | - | - | - | 100 | + | + | - | - | 200 | + | + | - | + |

Activity 2 (Table 2): Facilitated Diffusion Rates (glucose transport rate, mM/ min) Facilitated Diffusion (Glucose Transport rate, mM/min)
Discussion and Conclusions
In the first lab experiment (refer to Table 1), Simulating Dialysis (Simple Diffusion), the computerized simulation demonstrated the passage of water and solutes through semi permeable membranes in cells down its concentration gradient. The four membranes used in the experiment consisted of different pore sizes (MWCO). They ranged (from smallest to largest) at 20 (MWCO), 50 (MWCO), 100 (MWCO) and 200 (MWCO). The solutes that were tested were NaCl, Urea, Albumin, and Glucose. The first solute tested, NaCl, showed with a 20 MWCO membrane, no diffusion occurred into the deionized filled beaker on the right. The NaCl molecules were too large to pass through the 20 MWCO membrane because its pores were too small. Membranes 50 (MWCO), 100 (MWCO) and 200 (MWCO) did allow NaCl to permeate through and the reason being is because the pores in these membranes were large enough to permit passage of the NaCl molecules. The other reason diffusion occurred is because the NaCl molecules moved down its concentration gradient and into the beaker filled with deionized water. For all three experiments, equilibrium was reached in ten minutes at an average diffusion rate of 0.015 mM/min. As for the solute Urea, the experiment showed no diffusion in membranes 20 (MWCO) and 50 (MWCO). However, Urea did pass through membranes 100 (MWCO) and 200 (MWCO) because the molecules were small enough and soluble. Equilibrium was reached at sixteen minutes at a diffusion rate of 0.0094mM/min. The next experiment with the solute Albumin showed no diffusion in any of the four membranes tested. This is because the Albumin molecules were too large to pass through the pores of all four. Glucose, the final solute tested in the experiment, showed that the molecules only diffused through the 200 (MWCO) membrane. Equilibrium was reached in thirty-seven minutes at an average diffusion rate of 0.004 mM/min. Glucose molecules were too large to diffuse through the 20 (MWCO), 50 (MWCO), and 100 (MWCO) membranes.
The second experiment (refer to Table 2), Simulating Facilitated Diffusion, explained how carrier protein molecules in the membrane effectively transported molecules that were too large or insoluble to diffuse through the membrane. Carrier proteins in this experiment were glucose carriers and solution was 2.00 mM and 8.00 mM glucose concentration. The 2.00 mM glucose concentration was first tested with 500 glucose carrier protein membrane, then 700 glucose carrier protein membrane, and finally, 900 glucose carrier protein membranes. The glucose transport rate for the membrane with 500 glucose carrier proteins was 0.0008 (mM/min). The membrane with 700 glucose carrier proteins showed a rate of 0.0010 (mM/min) and 900 glucose carrier proteins membrane had a rate of 0.0012 (mM/min). The 8.00 mM glucose concentration also showed and increased in glucose transport rate with membranes that contained more glucose carrier proteins. The membrane with 500 glucose carrier proteins showed a rate of 0.0023 (mM/min). Membranes that had 700 and 900 glucose carrier proteins showed a rate of 0.0031(mM/min) and 0.0038 (mM/min). These results show that with an increase in amount of glucose carrier proteins in the membranes, transport of the glucose molecules in the concentration is more effective. A higher concentration of glucose at 8.00 (mM) also increases the rate of glucose transport in a membrane with the same amount of glucose carrier proteins as a lower glucose concentration of 2.00.

Reference List
Physio-Ex. Version 8: Laboratory Experiments in Physiology. CD. Pearson, 2008.
Human Anatomy and Physiology Laboratory Manual. Custom Edition for Collin College. Marieb, Elaine and Mitchell, Susan. San Franciso: Pearson, 2009.
Marieb, Elaine and Hoehn, Katja. Human Anatomy and Physiology. 8th edition. San Francisco: Pearson, 2010.