AP Biology Lab: Diffusion and Osmosis - Weebly



AP Biology Lab: Diffusion and OsmosisDriving QuestionsThe concept of transport across membranes is fundamental to understanding cell structure and function. In this lab, you will investigate diffusion, osmosis, and facilitated diffusion using artificial membranes, tissue cores, and individual cells.Is dialysis tubing a semipermeable membrane? What is it permeable to?Why is it important for an IV solution to have salt in it?What would happen if you were given pure water in an IV?How can you use the weights of the cell model to determine the rate of diffusion?Background432498520447000Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. For example, if one were to open a covered dish containing a rotten fish in the front of the lab, students on the front row would quickly recognize the molecule dimethylamine with their nose. Students in the back of the lab would succumb to the smell a few seconds later. The diemethylamine gas is highly concentrated in the rotten fish carcass, and diffuses into the less concentrated corners of the laboratory until a dynamic equilibrium is reached. What is a dynamic equilibrium? It is when the concentration of dimethylamine is approximately equal throughout the lab, and there is no net movement of the molecule from one area to another. 4229735122555H2OSolute00H2OSoluteOsmosis is a special case of diffusion. It is the diffusion of water through a selectively permeable membrane (a membrane that allows for diffusion of certain solutes and water) from a region of higher water potential to an area of lower water potential. Water potential is the measure of free energy of water in a solution. Recent research indicates that in many organisms (including plants) osmosis is actually a special case of facilitated diffusion. Water does move through the plant cell membrane, but water also moves more rapidly through membrane-bound channel proteins called aquaporins. Diffusion and osmosis do not entirely explain the movement of ions or molecules into and out of cells, or across intercellular membranes. Some of that movement is attributed to active transport. This process uses the energy from ATP to move substances across a membrane against the concentration gradient, from an area of low concentration to area of higher concentration.Materials and EquipmentFor each student or group:Part 1 – Osmosis Beakers or plastic cups (4), 250-mLElectronic balance (one per class)Graduated cylinder, 25-mLSmall funnelSoaked dialysis tubing (4), 30 cm longPlastic wrapUnknown sucrose solutions, (4)Labeling marker and tapeDistilled waterScissorsDisposable pipetsDental floss or stringSequencing ChallengeThe steps below are part of the Procedure for this lab activity. They are not in the right order. Determine the proper order and write numbers in the circles that put the steps in the correct sequence. -60960472440Place a dialysis bag containing a solution in a beaker containing DI water.Obtain dialysis tubing, cup or beaker, and appropriate solutions. Weigh again and determine change in mass and record results. Perform analysis of results.Record initial colors and molecular contents of dialysis tubing and cup or beaker.Allow experiment to run for 15 minutes.00Place a dialysis bag containing a solution in a beaker containing DI water.Obtain dialysis tubing, cup or beaker, and appropriate solutions. Weigh again and determine change in mass and record results. Perform analysis of results.Record initial colors and molecular contents of dialysis tubing and cup or beaker.Allow experiment to run for 15 minutes.Part 1 – Osmosis4872990106680001.Obtain four strips of soaked dialysis tubing. 2.Tie a knot in one end of each strip to create a bag. If you cannot tie a knot in the bag, try using dental floss or string. 3.For each of the four unknown sucrose solutions, perform the following steps:a.Use the graduated cylinder to obtain ~15 mL of an unknown sucrose solution. b.Fill one of the dialysis bags with the solution. You may want to use a funnel to help you fill the bag. c.Tie off the open end of the dialysis tubing. d.Rinse the outside of the bag with water, blot the outside of the bag with a paper towel, and place the bag on plastic wrap. Q1.Why should you place the bags on plastic wrap as opposed to a paper towel?4.Find the mass of each of the four dialysis bags, and record the data in Table 1.3. 5.Obtain four 250-mL beakers or cups. 6.Fill each of them two-thirds full with distilled water.7.Place each of the dialysis bags into a separate beaker or cup, making sure the bags are completely submerged. Label the beaker or cup in such a way that you know which unknown solution was placed in each beaker or cup.Q2.Do you think the bag will change shape during the course of the experiment? Why or why not?Q3.How can you determine the sucrose concentrations of the unknown solutions if you don’t label the cups?8.Let the dialysis bags soak for 30 minutes.9.Remove the bags after 30 minutes, and blot them quickly with a paper towel. 10.Find the mass of each of the bags again, and record data in Table 1.3.Q4.Why would you use the same balance that you used for the initial mass?Table 1.1: Individual group determination of sucrose solutionsContents in dialysis bag (color)Initial mass (g)Final mass (g)Mass difference (g)Change in mass(%)*Concentration of sucrose(M)Solution 1 (green)Solution 2 (red)Solution 3 (blue)Solution 4 (yellow)Table 1.2: Class determinations of sucrose solutionsContents in dialysis bag (color)Change in mass of dialysis bag (%)Class averageSucrose concentration [M]Group1Group2Group3Group4Group 5Group 6Solution 1 (green)Solution 2 (red)Solution 3 (blue)Solution 4 (yellow)Draw Graph 1.1. Plot the data from Table 1.1 on a graph showing "% change in mass of the dialysis bag (class average)" on the y-axis versus "sucrose concentration (M)" on the x-axis. Label the overall graph, the x- and y-axes, and include units on the axes. 1. What effect did increased sucrose concentration have on the mass of the dialysis bags in Part 2? Explain these effects in terms of tonicity and osmosis.2.Why did you calculate the percent change in mass rather than simply using the change in mass?3. Which of the following types of molecules are the major structural components of the cell membrane?A.Phospholipids and celluloseB.Nucleic acids and proteinsC.Phospholipids and proteinsD.Glycoproteins and cholesterol4.Water passes quickly through cell membranes becauseA.The bilayer is hydrophilic.B.It moves through hydrophobic channels.C.Water movement is tied to ATP hydrolysis.D.It is a small, polar, charged molecule.E.It moves through aquaporins in the membrane.5. Which of the following statement is correct about diffusion?A.It is very rapid over long distances.B.It requires an expenditure of energy by the cell.C.It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.D.It is an active process in which molecules move from a region of lower concentration to one of higher concentration.E.It requires integral proteins in the cell membrane.6. A patient is in a serious accident and loses a lot blood. Distilled water, in equal volume to the blood lost, is transferred into the patients veins. What is the likely outcome of this transfusion?A.It will have no unfavorable effect as long as the water is free of viruses and bacteria.B.The patient's red blood cells will shrivel up because the blood fluid is hypotonic compared to the cells.C.The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.D.The patient's red blood cells will shrivel up because the blood fluid is hypertonic compared to the cells.E.The patient's red blood cells will burst because the blood fluid is hypertonic compared to the cells. 7. Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in salt solution become limp and soft. From this we can deduce that the cells of the celery stalks areA.Hypotonic to both fresh water and the salt solution.B.Hypertonic to both fresh water and the salt solution.C.Hypertonic to fresh water but hypotonic to the salt solution.D.Hypotonic to fresh water but hypertonic to the salt solution.8572536576000E.Isotonic with fresh water but hypotonic to the salt solution.-10668055245123450012345Which beaker(s) contain(s) a solution that is hypertonic to the bag? Which bag would you predict to show the least change in mass at the end of the experiment? Arrange the beakers in order of the mass of the bags inside them after the experiment has run for 30 minutes. List the bag that loses the most mass first. ................
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