In this lab we will establish a difference between the two types of cell transport mechanisms and their permeability. The first type of cell transport is passive processes which are driven by concentration or pressure differences in the interior and exterior of the cell. The second type is active processes which use energy known as ATP to power the transport. There are two main types of passive processes called diffusion and filtration. This can be split into different types such as simple diffisuion, facilitated diffusion, osmosis and filtration.
The objective of these experiments is to provide information on the passage of solutes and water through semi permeable membranes and relate them back to the study of actual living membranes in the human body. The purpose is to better understand how and why membranes use certain types of passive or active processes to move solutes and water across its membrane.
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Simple diffusion is the net movement of substances from a region of high concentration to a region of low concentration. It will move down its concentration gradient meaning the molecules will eventually become evenly distributed throughout the environment. In this experiment NaCl, urea, albumin and glucose will be used to show how different substances move differently across the membrane. If a substance is not able to go across a membrane then the size of particles are to large to pass through, but other particles depending on size should still be able to pass through.
Facilitated diffusion is also the net movement of substances moving down their concentration gradient, but with the help of carrier proteins. Which are proteins that bind to substance or molecule and help it transport across the membrane. In this experiment we will use different concentrations of glucose to show the affects carrier proteins have on its permeability. If glucose is not able to pass through the membrane then either there are no carrier proteins present to help or not enough to help finish the process.
Osmosis is a special form of diffusion which solely relates the movement of water thorough a membrane. It occurs when there is a difference in water concentration on both sides of a membrane. The concentration of water in a solution depends on the number of solutes present. It will always move to the solution with the highest concentration of solutes. In this experiment NaCl, albumin, and glucose will be used to help show the movement of water across a membrane. If water is not able to diffuse across a membrane then it has either reached equilibrium or the concentration of solutes was lower on the other side.
Filtration is the process where water and solutes pass through a membrane from an area of higher hydrostatic pressure to an area of lower hydrostatic pressure. Meaning the pressure on either side of the membrane is what pushes or decides whether or not the water and solutes will be able to pass through. In this experiment NaCl, urea, glucose, and powdered charcoal will be added to water to help show how solutes and water will pass through a membrane depending on the pressure. If the hydrostatic pressure is high enough then all the solutes and water will able to pass through the membrane.
Active transport, the only active process, uses cellular energy ATP to help move solutes across the membrane. This is used when all other passive processes are not able to get a solute or substance across the membrane for a number of reasons. In this experiment we will demonstrate a sodium potassium pump to illustrate how ATP is needed to get both NaCl and K across the membrane. If there is not enough ATP for the transport then the transport will not occur.
Materials and Methods
For these experiments I used the Physio EX 8 on the my lab and mastering website study area. I followed the instructions in the Anatomy and Physiology lab manual on pages 53-63.
The results and data from the experiments are presented in several charts attached to the lab report. In the chart labeled simple diffusion it shows the size of the membrane, starting concentration in both the left and right beaker, and the average rate of diffusion. In the chart labeled facilitated diffusion it shows the starting concentration of the left and right beaker, the number of carrier proteins and the rate of diffusion. In the chart labeled osmosis it shows the size of the membrane, starting concentration of both left and right beakers, the hydrostatic pressure, and rate of diffusion. In the chart labeled filtration it shows the size of the membrane, pressure, the rate of filtration, if residue was present in the membrane, the starting concentration and the filter concentration. In the chart labeled active transport it shows the amount of ATP, the starting concentration of both the left and right beaker, amount of sodium potassium pumps, number of carrier proteins and the rate of diffusion.
According to the results found in the simple diffusion experiment we were able to support the hypothesis. Depending on size, some particles were able to diffuse while others were too large to pass through. For NaCl it was able to pass through three out of four membranes, once able to pass through it had a constant average of diffusion at .0150. Urea was able to pass through two out of four membranes, and also once through it had an average rate of .0094. Albumin was not able to pass through any of the membranes, due to the fact the particles were to large and the membrane pores were too small for them to pass. Unlike Albumin, Glucose was only able to pass through the largest membrane. No other experiments were run due to the fact the results clearly showed a relationship between size and permeability of a membrane.
In the results of the facilitated diffusion portion we were able to partially support our hypothesis. Glucose was able to pass through the membrane with help from carrier proteins. If diffusion did not occur it was not solely for the reason carrier proteins were not present, but because equilibrium had already been reached on both sides of the membrane. As carrier proteins in the solution increased the rate of diffusion also steadily increased, the same was for an increase in the amount of glucose in the solution as well. To further test the relationship we added NaCl to the solution to see if it had an effect on the rate of diffusion. It was able to pass through the membrane, but did not change the rate of diffusion for glucose in the specific membrane.
In the osmosis experiment the results rejected the hypothesis because many more variables affect whether or not water is able to pass through a membrane. The diffusion of NaCl through the membrane was possible only in membranes were the pore of the membrane was large enough for the solute to pass through. If it was not able to pass through, but was not at equilibrium on both sides pressure would build in the more concentrated beaker. If the solute was able to pass through it would have a constant rate of diffusion no matter the size of the membrane. Albumin was added to the solution, but was not able to pass through any of the membranes since the solute was too large, but the pressure was constant through every size membrane. When glucose was added it was only able to pass through the largest membrane, but also had a constant pressure in membranes it could not pass through. To further understand the relationship of membranes and solutes in osmosis we did a few extra experiments. When the same amount of Albumin was added to each side of the beaker no diffusion occurred nor did pressure build in the beaker because the solutions started at equilibrium and would not move across the membrane.
The filtration experiment data rejected the hypothesis because the diffusion was affected by more then just the hydrostatic pressure. I believed it was more like an all or nothing door, if the pressure was great enough then all the solutes would pass through together. That is not the case, the size of the membrane also matters in what can or can not pass through as well as not all solutes will pass though certain membranes making it semi permeable. This was evident in the results when we decided to run an experiment with the same starting concentration and same size membrane, but different pressures. In both runs no solutes were able to pass even though the pressure behind it had increased by 50, the pressure did not affect the solution enough to pass through the membrane since the solutes were to large to pass through membrane in the first place.
In the final experiment where we tested active transport we only half way supported our hypothesis. The presence of ATP is important for the process to occur, but it is not an all or nothing process. The transport will continue till no more ATP is left over and then will have to stop until more is present. Also affecting the diffusion is the amount of carrier proteins present to help with transport, without the proteins diffusion would not be possible. In this experiment it represented the sodium potassium pump which the solutes presences directly affects whether or not the process will occur, because without one or the other the process would not be able to occur at all. This was evident in the experiment when we withheld potassium from a run no diffusion occurred even though proteins carriers and ATP were present.
From these experiments we can conclude that permeability of a solute across a membrane is affected differently from process to process. Each process has similar variables that will affect the rate or capability to diffuse, but some require more work, energy or other substances needed to allow diffusion to occur. Each type of diffusion plays a key role in the homeostasis of a cell and is needed for normal life functions to occur. With out the different specific types of processes some solutes would never be able to pass through a membrane or there would be no control of how much or when a solute is allowed to cross over.
The only problems to arise during the experiment was not being able to login to the my lab and mastering website during the middle of running my experiments, due to an error in the server. I eventually tried another computer and was able to login with no problems.
Throughout the experiments I considered the fact that the results found are free from human error since it is a computer simulation, but does that make them more or less accurate since it’s a simulation then an actual live experiment. The processes have been sped up to make it more time manageable, but can that accurately represent diffusion through a membrane. To better answer these questions one would need to do that exact same experiments, but in real time with no help from a computer program.
- Human Anatomy & Physiology Laboratory Manual, Cat Version, Update, Ninth Edition by Elaine N. Marieb and Susan J. Mitchell. Copyright 2009 by Pearson Education, Inc. Published by Benjamin Cummings. San Francisco, California 9411
- "MasteringA&P." MasteringA&P. N.p., n.d. Web. 18 Sept. 2013.
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