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Investigation 4 Diffusion and Osmosis

Investigation 4 Diffusion and Osmosis. Investigation 4. Part 1: Surface Area and Cell Size Part 2: Modeling Diffusion and Osmosis Part 3 Observing Osmosis and Living Cells. The Background reading really frames this…. A great way to begin is to pair-share the questions on page S54.

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Investigation 4 Diffusion and Osmosis

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  1. Investigation 4Diffusion and Osmosis

  2. Investigation 4 • Part 1: Surface Area and Cell Size • Part 2: Modeling Diffusion and Osmosis • Part 3 Observing Osmosis and Living Cells

  3. The Background reading really frames this… • A great way to begin is to pair-share the questions on page S54. • This gives you information of prior knowledge and alerts you to misconceptions.

  4. Lab 4 Procedure 1Modeling Surface Area and Cell Size • Wear your safety eyewear • Wear your apron or lab coat • Wear your closed toe shoes • The agar cubes are soaked in a 0.01% NaOH solution. Caution • The agar cubes have been prepared with 1% phenolphthalein, which is a pH indicator.

  5. Acid or Base? • Phenolphthalein Color Indicator

  6. You have been given, or will cut, 3 agar blocks. (See page S56-S58) • These are models for your cells. • Wearing your gloves, measure the surface area of each “cell.” • Calculate the volume. • In your journal, predict which block will show the fastest diffusion. • Perform an experiment to test your prediction. • Analyze your data. • Return your blocks and solution to a collection spot for disposal.

  7. Extent Diffusion as a percent of total (Total cube volume-Volume that has not changed color/Total volume) x 100 Percent Diffused Surface Area/Volume

  8. These are cells and tissues with specialized functions. Think about their similarities in shape, size, nutrient procurement. Discuss. http://www.technion.ac.il/~mdcourse/274203/slides/Digestive%20tract/17-Intestinal%20villi%20Jejunum-A.jpg http://www.cytochemistry.net/cell-biology/actin.6.gif http://iweb.tntech.edu/mcaprio/roots.htm

  9. Check your work (formative) • Did you record all your data appropriately? • Did you measure using a metric ruler? Did you rinse the ruler off after use? • Did you calculate rate of diffusion for each cube in cm/min? • Did you graph this as a function of SA/Vol? • Did you calculate the extent diffusion as a percent of the total volume? • Did you graph the extent diffusion against surface area/volume?

  10. Lab 4, Procedure 2Modeling Diffusion and Osmosis • Found on page S56-S58 in the student lab book. • Complete lab steps 1-4 p. S57. • During your 30 minute wait time look at osmosis in the red onion and/or elodea (Procedure 3, steps 1-2).

  11. Onion Osmosis Using Image J

  12. Before Starting… • You need to have • A microscope • A red onion • Something to cut with (scalpel or razor) • A slide and cover slip • Some 15% salt solution and a pipette • A piece of paper towel • A clear metric ruler • Image J installed (free at NIH.gov) • You need to know • The diameter of the field of view of your microscope. • Directions follow.

  13. How to: Microscopic Measurement Determine the diameter of your “field of view.” 1. Begin with a clear ruler. 2. Place on the stage, visible under the lowest magnification for your microscope. 3. Determine the diameter of the field of view in mm. 4. 1mm=1000 Micrometers (μm) 1 mm

  14. How to: FOV under a higher power lens For a higher power, you need to calculate the field of view.

  15. Zoom in • (Original Obj/New Obj) x Original FOV=New FOV • FOV=Field of View 15

  16. Onion Osmosis Analysis with Image J

  17. Cut a piece of outer pigmented tissue

  18. Make a wet mount

  19. Add concentrated salt solution

  20. Take a picture through the microscope.Save to computer.

  21. Determining Percent Change in Area Find your file and open it.

  22. To get area and perimeter... Select the straight line tool. Drag across your field of view.

  23. Under analyze: Set scale

  24. Pixels are already there. Enter your known distance.

  25. Analyze: Set Measurements

  26. Trace with the freehand toolGo to analyze: Measure Compare before and after

  27. Calculate • Percent change in area • Percent change in perimeter.

  28. Let’s look at Water Potential If we soak potato CELLS in a sucrose solution which way will water move? Water always moves from a higher water potential to a lower water potential.

  29. Look on the Formula Sheet Ψ = Ψp + Ψs Pressure Potential Water Potential Solute Potential Water always moves to a lower, more negative, water potential.

  30. Ψs= Solute Potential Ψs Solutes are always negative More solutes = more negative Which way will water move? What is happening to the pressure potential in cell?

  31. Ψp= Pressure Potential Usually Positive

  32. Water Potential in the Potato Cells • Update your definition of osmosis: Osmosis is the movement of water molecules through a selectively permeable membrane from a region of higher water potential to an area of lower water potential. • Water always moves to a more negative water potential.

  33. Water PotentialCan we figure out the water potential of a cell in a solution at equilibrium? • Ψ= Ψp + Ψs • Where there is no % change in mass, the solution in the beaker has the same water potential as the potato cells. Dynamic Equilibrium

  34. Water Potentialat Equilibrium Ψ of Solution in Beaker = Ψ of Potato = (Ψ= Ψp + Ψs) = (Ψ= Ψp + Ψs) Potato cells

  35. Water Potential Solution Potato Cells (Ψ= Ψp + Ψs) = (Ψ= Ψp + Ψs) (open beaker) Ψ=Ψs+(Ψp= 0) = Ψ= Ψp + Ψs Ψ=Ψs = Ψ= Ψp + Ψs Ψs = Ψ= Ψp + Ψs Pure water at atmospheric pressure has a water potential of zero.

  36. Collect Temperature of liquid! Potato Core Results- What elements are needed in a good graph? Discuss trends, errors. Your lab group should be prepared to use the terms hypertonic, hypotonic, isotonic as they report to the class.

  37. To CalculateΨs Ψs = -iCRT i= Ionization constant (sucrose is 1.0 because it does not ionize). C= Molar Concentration (from line of best fit where the line crosses the x axis) R= Pressure Constant (0.0831 liter bars/mole °K T= Temperature °K (273 + °C)

  38. An example • Ψs = -iCRT • Ψs= -(1.0)(0.36 mole/liter)(0.0831 liter bar/mole °K)(295 °K) • -8.83 bars • This equals the entire Ψof the cell.

  39. Lab 4 Procedure 3 • Design your experiment. • Use the concept of water potential (formula sheet) • Complete lesson 6 in your WB as you go. • Plan to share your results.

  40. Assessment • Excerpt from “The Rime of the Ancient Mariner” by Samuel Taylor Coleridge. This is a poem about a sailor on a ship. • Water, water everywhere, • And all the boards did shrink; • Water, water, everywhere , • Nor any drop to drink. • Why did the boards of the ship shrink? • Why couldn’t the mariner drink any of the water? From BSCS Biology 9th ed

  41. Summative Assessment • See page T91 for suggestions.

  42. Resources • Mr. Anderson on Water Potential https://www.youtube.com/watch?v=nDZud2g1RVY • Osmosis in Elodea https://www.youtube.com/watch?v=zVvHn6Sj9PQ • AP Biology Teaching Tips #5 Osmosis and Image J: https://youtu.be/d75A_gBpRCk

  43. Misconceptions • Osmosis and Diffusion Conceptual Assessment • Fisher, K. M., Williams, K. S., & Lineback, J. E. (2011). Osmosis and diffusion conceptual assessment. CBE life sciences education, 10(4), 418–429. doi:10.1187/cbe.11-04-0038

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