I. AbstractTransport through membranes either directly through the layers orthrough carriers such as carrier proteins in cell membranes occur via one oftwo basic processes: diffusion or active transport (Halland Guyton, 2016). Diffusion means random molecular movement of substancesmolecule by molecule, either through intermolecular spaces in the membrane orin combination with a carrier protein. In contrast, active transport means movement of ions or othersubstances across the membrane in combination with a carrier protein in such away that the carrier protein causes the substance to move against an energygradient, such as from a low-concentration state to a high-concentration state. In this exercise, the movement ofsubstances placed at different concentrations with respect to its surroundingenvironment were observed. Our results show that substances with no active carriersgenerally move from a place with higher concentration to places with lowerconcentration in the purpose of reaching equilibrium. As substances naturallymove toward low concentrations, the presence of semi- permeable membranes aidin the separation of different substances by restricting the movement of somesubstances. This exercise will help us understand the physiological movementsof different substances and how membranes help achieve different movementprocesses.
II. ResultsDiffusion1. Diffusionof gas in a gasThe scent of theperfume was detected at different time intervals in different distances (Table1.
1). As the distance increased, the time it took for the perfume to bedetected also increased.Table1.
1. Times to reach the distances as the perfume was uncapped. Distance (m) Time 1 18.3 sec 2 1 min 39 sec 3 2 min 05 sec 4 3 min 38 sec 5 4 min 56 sec 2. Diffusionof a solid in a colloidal solutionThere weredifferences in the rate of diffusion of the three substances placed in thecolloidal solution. After an hour, the substance with the lowest molecularweight, KMnO4, diffused the fastest while the substance with thehighest molecular weight, methylene blue, was the slowest.
Potassium permanganate: =0.402 mm/minPotassium dichromate: =0.225 mm/minMethylene blue: =0.017 mm/minFigure 1.1. Rate of diffusion of three substances in relation to its molecularweight.3. Diffusionof a solid in a liquidUpon addition ofthe sodium permanganate crystal in the water, the color did not spread rapidly.
First, the color occupied the bottom of the water then it gradually rose to thetop part of the water. Eventually, after about 30 min, all of the water in thebeaker was colored equally (Fig. 1.2).Figure 1.2.
Diffusion of potassium permanganate.OsmosisUsing the linegraph we were able to see the pattern of the changes of the weight of thedialyzing membrane over time (with 5-minutes intervals). It is clear that thedialyzing bag increased intensely on its first interval compared to thefollowing intervals. However, based on the graph, the dialyzing bag have lostweight upon its 3rd interval, which was then again followed by aweight increase on the 5th and 6th interval.
Figure 1.3. Weight changes ofthe dialyzing membrane containing NaCl.Based on theprojected line graph, the weight of the dialyzing bag decreased intensely onits first 5-minute interval compared to the following intervals. There is alsoan evidence that the weight of the dialyzing bag did not decrease constantly,but rather followed an interchanging pattern per interval. Lastly, it can beobserved that the weight remained lower in all intervals compared to thepre-immersion weight.
Figure 1.4. Weight changes ofthe dialyzing membrane containing H20.Hemolysisand crenation The red blood cells (RBCs) mixed with the 3% sodiumchloride (NaCl) was wrinkly in shape. The smooth edges of the RBCs were goneand the original shapes of the cells were also lost (Fig.
). On the other hand,the RBCs exposed to distilled water were also not the original shape. The cellswere rounder and some of the cells had burst (Fig.
). The RBCs exposed to the0.9% NaCl, however, did not show any changes to the cell (Fig. ). C B A Figure 1.5. Effects ofhypertonic (A), hypotonic (B), and isotonic (C) solutions on cell volume.
DialysisA. Test for sodium chloride Upon the addition of silver nitrate (AgNO3) tothe test water, the test water which was previously clear became turbid. Thisis because of the slight formation of white precipitates. The result indicatesthat the sodium chloride (NaCl) which was previously inside the dialyzing bagwas able to pass through the membrane of the bag. B. Test for starch When the IKI solution was added into the testtube containing the test water, the IKI solution remained its color as it is.The formation of a blue-black colored solution was expected in this test to beable to confirm that starch is present in the test water. However, the solutiondid not transform its color.
This means that the dialyzing membrane did notallow the starch to pass through. C. Test for glucose In thistest, a precipitate with either of the colors: green, yellow, or brick redshould appear if glucose is positive in the test water. Upon the addition ofBenedict’s solution the resulting solution, however, did not change into eitherof the anticipated colors.
The solution remained blue as the color of theBenedict’s solution is blue. Thus, we were able to confirm that the dialyzingmembrane did not allow the glucose to pass through it. D. Test for albumin Concentratednitric acid (HNO3) was added to the test water drop by drop.However, a white coagulum, which is supposed to form in the presence ofprotein, did not appear. This result indicates that the test water was negativeof any protein from the egg albumin.
The dialyzing membrane did not allow theprotein components of the albumin to pass through it.a. b. c. d.
Figure 1.6. Results fordialysis tests. a= test for sodium chloride b= test for starch c= test forglucosed= test for albumin III. DiscussionDiffusion Diffusion, according to Hall and Guyton (2016),is a random, constant motion of molecules that are moving from an area of highconcentration towards an area of low concentration. Furthermore, the rate ofdiffusion is affected by certain factors such as temperature, viscosity of themedium, and the molecular size of the particle.
The experiment was able todemonstrate how these factors affect the rate of diffusion.Gaseous particlesare inclined to undergo diffusion due to the presence of kinetic energy (Malone and Dolter, 2010).This energy enables the particles to move at a constant, random motion. Asstated previously, these particles will travel to an area with lowerconcentration. This was observed during the experiment when there was a gradualdetection of the scent in order of the distances.
The farthest distance wasable to detect the scent lastly which clearly displays the diffusion of gas ina gas. The secondexperiment was performed to determine the effect of molecular weight to therate of diffusion. As molecular weight increases, the rate of diffusion decreases(Fig. 1.1).
This implies that the rate of diffusion of a substance in inverselyproportional to its molecular weight under the same conditions. The smallerweighing substances are able to migrate more rapidly because they encounterless frictional drag in the gel (Malone and Dolter, 2010)which is why potassium permanganate diffused the fastest compared to potassiumdichromate and methylene blue.The same conceptapplies when a solid substance diffuses in a liquid solution – it travels downits concentration gradient. The process is gradual until it can cover the wholemedium.Several factorsaffect the rate of diffusion in different media. Gases diffuse faster thanliquids, and liquids diffuse faster than solids. Nonetheless, the same factorsapply to the different phases of matter.
Osmosis Osmosis playsa primary role in biological systems. The exchange of matter with the medium inall living organisms occurs in such a mode. Osmosis is a physicochemicalprocess, in which the concentration difference between two solutions createspressure difference (osmotic pressure) across a separating semipermeablemembrane. Solvent transport takes place from the more diluted solution to thatof higher concentration, until equilibrium is reached (Minkov et al., 2013). Asolution is said to be isotonic when both sides of the membrane has an equalconcentration of solute. On the other hand, if one side of the membrane hashigher concentration of solute compared to the other, it is then considered ashypertonic, where water tends to move in that direction.
Lastly, the other sidewhich has lesser concentration of solute compared to the other is considered tobe hypotonic (Galindo, 2003). In this experiment, we were able to see how the watertook its action as soon as the dialyzing membrane containing NaCl was immersedin the beaker. The water moved into the bag rapidly which caused a suddenincrease of the weight of the bag. In addition, it can be observed in the graphthat the water movement has almost reached equilibrium since the followingintervals had already small changes of its weight.
The NaCl inside thedialyzing bag indeed caused a hypertonic solution and so thus the water wentinside to reach equilibrium for both the solute and the solvent. The second dialyzing bag contained water and was immersedin a beaker containing NaCl. As expected, the water went outside the membranewhich caused a rapid weight decrease of the bag. The solution has reachedequilibrium upon its first interval.
It was expected that the weight of the dialyzingbag would continually decrease or may stop decreasing when it reachesequilibrium. However, there were some fluctuation in the data. This could bedue to improper handling of the test. As the dialyzing membrane was removedfrom the beaker from time to time in order to weigh, the dialyzing bag may notbe dried as constantly as how it was dried on the other intervals. This casecould be the reason for the fluctuations of the data.Hemolysisand crenation The cell membranes of the blood are also permeable towater, like any other cell (Mader et al., 2013).
However, ions that are also in the solution cannot pass through the membranedue to its larger size compared to water. The process that governs thismovement of water from one side of the membrane to the other is called osmosis(Hall and Guyton, 2016). In addition, this process is controlled by thedifference in the ion concentration in the solution and inside the cell.
The shrinking ofa cell is called crenation (An et al., 2014).Crenation occurs when the cell is exposed to a solution that has a highersolute concentration than inside of the cell.
The cell releases its water tothe outside in response to the concentration of the outside environment causingit to shrink. When this happens the solution is said to be hypertonic (Hall andGuyton, 2016). This suggests that 3% NaCl is hypertonic to the RBCs.According to Halland Guyton (2016), when the cells are exposed to a solution with a lower soluteconcentration than the inside of the cells, the cells take in water from theoutside. The solution is hypotonic to the cell. As the cells take in water,this causes them to swell and eventually burst.
This is called hemolysis (Hall and Guyton, 2016).Exposure to distilled water caused the RBCs to swell and burst so the solutionis hypotonic to the RBCs.The RBCs remainedin their original state when exposed to 0.9% NaCl. If it neither shrinks orswells, the solution ishence isotonic. Therefore,solutions with concentrations of more than 0.9% is hypertonic to the cell andsolutions with concentrations lower than 0.9% is hypotonic to the cell.
DialysisDialysis is known as the process of separating largermolecules from smaller molecules (Galindo, 2003) by means of a passive movement in whichthe mobility of solute particles between two liquid spaces is restricted,mostly according to their size. Size restriction is achieved by using a porousmaterial, usually a semi-permeable membrane called dialysis membrane. Thismembrane is permeable only for particles below a certain size. There are alsosome cases where restriction of diffusion is driven via polarity or charge (Hegyi and Kardos, 2013).In this experiment, a pork intestine is used as adialyzing bag which is supposed to allow the small molecules that are smallenough to pass through its membrane. Among the substances that was placedinside the bag, it appeared that only NaCl was able to move into the outside ofthe bag while the rest remained inside as the test water was confirmed to benegative of it. Because of this ability to separate substances, the dialyzingbag was considered to be selectively permeable. The result of this test was more likely determined by thesizes of the substance, as described by (Hegyi and Kardos, 2013).
However, another factor could also be the reason for the restrictionof the other substances inside the dialyzing bag. Aside from the size of thesubstance, its fat- solubility also controls its ability to pass through thedialyzing bag since the one used in the experiment is an intestine which has acharacteristic of a lipid bilayer. Movements of water- soluble substances areimpeded in a lipid bilayer (Halland Guyton, 2016). Carbohydratemolecules such as starch and glucose (Hall and Guyton, 2016), and albumin protein molecules aregenerally water-soluble (Cooper, 2000). This explains why suchsubstances where not present in the test water since they cannot freely passthrough the membrane.