Diffusion Through A Membrane Lab

Diffusion Through a MembraneWhy are we dong this lab?This lab is designed to help us become familiar with the nature of ?the cell membrane, diffusion, and osmosis. The Lab is divided into two major parts: The first part involves making a model cell with glucose and starch inside and the placement of this cell into a beaker with iodine.The second part involves the observance of osmosis using red onion cells. To examine each part in more detai or scroll through the pages.Part 1Part 2Diffusion Through a Diffusion of Water Across Membranea Membrane (Osmosis)A. Making The CellA. Making the SolutionB. Testing the IndicatorsB. Applying the Hypertonic SolutionC. Using Indicators to Make a ConclusionC. Applying the Hypotonic SolutionDiffusion Through a Part 1MembraneA. Making The CellLet's get goingAfter opening the artificial membrane, tie off one end and add the glucose and starch solutions. Tie the other end then mix by gently turning the cell Glucose & upside down repeatedly.Starchafter making the cell put it aside for twenty minutes and then observePlace the cell in a beaker then add some iodineGlucose Observe any changes after & Starch20 minutesIodineDiffusion Through a Part 1MembraneB. Testing the IndicatorsIn order determine which substances diffused across the cell membrane we'll need to use some chemical indicators.Of course we will need an indicator for glucose and an indicator for starch.Glucose IndicatorStarch IndicatorLet's figure out how each indicator works.When the glucose When the starch indicator is heated in Positive indicator is in the Positive the presence of presence of starch it glucose it will turn a will turn a dark blue/brick red colorblack colorSince we have not used these indicators before it is necessary to verify that it is GlucoseStarchthe combination of the two substances WGlucoseStarchaterthat will cause the change by testing Waterthem individually. Diffusion Through a Part 1MembraneC. Using Indicators to make a conclusionWOW! After 20 minutes we The color changed At this point we need to observe that the inside of inside the cell. What use our knowledge of the the cell has changed color happened?indicators used earlier to and the outside has not.figure out which molecules moved across the membrane. The blue/black color change indicates that there is starch inside the cell and no starch outside the Glucose indicatorcell.Glucose & Starch10 drops added to test tubeWhat about the glucose? IodineDid it move across the cell? In order to figure this out we need to test the liquid outside the cell for glucose using the indicatorTen drops are removed and added to a test tube with glucose indicatorand then heated. The Blue solution should turn brick red if the glucose is outside the cell.Diffusion of Water Across Part 2a Membrane (Osmosis)A. Making the SolutionA solution has two parts: the solvent and solutesolutesolvent10g10 mlWe measured out 10g of salt and added it to 10ml of water. This is a hypertonic solution compared to the solution of the cytoplasmSolutionMore solute = hypertonicSolutions can be:Hyper-tonicIf we say a solution is hyper, hypo, or isotonic we must Hypo-toniccompare it to another solution.Iso-tonicHyper = AboveHypo = BelowIso = EqualThe prefixes refer to the amount of solute in the solutionDiffusion of Water Across a Membrane (Osmosis)Part 2B. Applying the Hypotonic SolutionMore solute = hypertonicThe hypertonic (salt water) solution is added to the slideWater leaves the cellsC. Applying the Hypotonic SolutionLess solute = hypotonicThe hypotonic (distilled water) solution is added to the slideWater enters the cellsDiffusion of Water Across Part 2a Membrane (Osmosis)SummaryThe key to understanding which way water will move is to figure out where the highest concentration of water is. It will flow from high to low concentration. Simply locate the area where the percentage of water is greatest - this is where the percentage of solute is lowest.Pure (distilled) water is 100% water and 0% soluteYou can see why the more salt you add to a solution the faster the water will leave the cell. As we add salt (solute) to a solution we decrease the percentage of water.10% Salt90% waterRed Onion Cellon a slide15% Salt85% wateraddedafter several minuteswater leaves the cell0% Salt100% wateradded