3 Diffusion = “high to low is the way to go!” Quote from Billy S. Osmosis = is the net movement of waterfrom a region of high water concentrationthrough a semi-permeable membrane toa region of low water concentration. Thismovement of water is driven by a differencein solute concentrations on the two sidesof the membrane
4 A Hypertonic Solution has a higher solute concentration than the solution to which itis being compared. A hypertonic solutionis the solution with the higherconcentration of solutes.A Hypotonic Solution has a lowersolute concentration than the solutionto which it is being compared. A hypotonicsolution is the solution with the lowerIsotonic solutions have the samesolute concentrations. The solutionsbeing compared have equal concentrationof solutes.
6 Red Onion Cells Question: How do tap water and salt water solution surrounding a red onion cell influence osmosis?
7 Materials: red onion epidermis, forceps or fingernails, dropper, tap water, salt solution, paper towels, microscope,slide, and cover slip
8 Make a wet mount of the red onion epidermis. …The purple pigment is concentrated in the top layer.…It is not easy to peel off a THIN red onion skin.…Too thick and the osmostic action will not be observedbecause too many cells crowd the slide—layer upon layer.…A thin skin curls up on itself and must be placed flat against the slide—or again, too many cell layers will impede the osmotic observation.…Be careful flattening the skin so that you do not rupture the cellsin the process and lose the purple pigment.
9 Step 1: Obtain a clean slide Use forceps or fingernails to peel away a single cell layer(purple region) add a water drop covering the onion cellsStep 3: Place a cover slip overthe onion cells
10 Examine under low power. …Find few pockets of intact cells with purple inside.…Focus your work on these cells.…When you have a clear view switch to medium power.Cell membraneat the edge ofthe purpleCell WallYellowish areaMake a labeled drawing, (SketchA) time viewed, title, name of cell, magnification viewed, and short description. This will give you a record of the original appearance of the onion cells.
11 Take a dropper and add several drops of salt solution to one side of your cover slip while placinga small piece of paper towelalong the opposite edge of the cover slip.The paper should draw out the waterand draw in the salt solution.Observe the effects of the sodium chloride(salt) solution on the onion cells.Salt waterPapertowelSlideCoverslipOnion cells
12 Plasmolysis Animation Red Onion CellPlasmolysis AnimationAnimation PlasmolysisElodeaOsmosis TugorAnimation
13 Plasmolysis Once the salt solution (hypertonic) baths the red onion cells (hypotonic cytoplasm), the net movement of wateris from the hypotonic cytoplasm of the red onion cellstoward the hypertonic salt solution surrounding the redonion cells. The cells’ cell membrane pulls away fromthe cell wall as noted by the edge of the purple pigment.PlasmolysisMake a properly labeled, careful drawing (SketchB) of the cells' appearancein a second sketch. Time viewed, title, name of cell, magnification viewed, and short description. This will give you a record of the appearance post-salt solution.
14 Question: What will occur when the red onion cells are bathed in tap water?TAP waterPapertowelSlideCoverslipOnion cellsMake a properly labeled drawing (SketchC) of the cells' appearance after replacementwith the tap water. Time viewed, title, name of cell, magnification viewed, and short description. This will give you a record of the appearance post-salt solution.