Background Information

Activities

General Outline

There are a handful of simulations you may wish to assign to the students before class as prelab assignments to prepare them for the exercises. These also emphasize the Vision & Change Core Competency of utilizing simulations.

Temperature/Diffusion Simulation

Size/Mass/Diffusion Simulation

Simulation of diffusion through a semipermeable membrane

  1. Review components of a cell membrane (Structure and Function)
  2. Review the concept of diffusion
    1. Discuss the difference between solute and solvent
    2. Discuss concentration gradients and energy
      1. Temperature/Diffusion Simulation (Modeling and Simulation)
      2. Size/Mass/Diffusion Simulation (Modeling and Simulation)
      3. Use ink under instructor microscope to illustrate Brownian Motion
  3. Set up demonstrations for diffusion
    1. Perform demonstration of crystalline solute in a beaker
    2. Set up the activity Do larger things diffuse faster?
      • This will be reviewed at end of class
  4. Discuss osmosis as a special case of diffusion
    1. Review the semipermeability of membranes
    2. Discuss the resulting osmotic pressure from solvent movement
    3. Work through and set-up Gummy Bear Tonicity to be reviewed at the end of class (Process of Science)
  5. Set-up demonstration experiments for dialysis tubing
    1. Set-up demonstration of phenolpthalein in dialysis tubing in beaker of NaOH
    2. Set-up demonstration of dialysis tubes with starch in iodine solution
  6. It is best to synchronize the class with 1.5 hours remaining for the main activities (Observing Osmosis and Why Are Cells Small?) (Quantitative Reasoning)
    1. Have the students set up the Observing Osmosis activity
      1. Have students record initial weights and fill table
      2. Synchronize so that they submerge the tubes at the same time
      3. During the first 10 minutes interval, have the students work out the table for Hypothesized Movement of Solution Based on Tonicity
      4. Continue the collection of data every 10 minutes. Synchronize the times in order to proceed to final exercise
    2. Intersperse the following demonstrations during first 10 minute interval
      1. Prepare a mount of sheep blood on the instructor scope.
        1. Demonstrate the effect of a hypertonic solution on the red blood cells
        2. They are very small but the shape change is obvious
      2. If you are provided with red onion, peel a thin layer of skin and prepare a wet mount under instructor microscope
        1. Use a Kimwipe to draw the solution from one side while dropping high saline solution on opposite side of coverslip
    3. During the second 10 minute interval, work out Data Table: Calculating Surface Area-to-Volume Ratio (Quantitative Reasoning)
    4. A couple of minutes after the third 10 minute interval, have the students immerse their cubes in NaOH
    5. During the fourth 10 minute interval, they can retrieve the cubes and cut the on paper towels
      1. Have the students work through the Calculation of Diffusion Area-to-Volume
  7. Wrap up the lab with review of the demonstrations (Process of Science)
    1. Pour out solutions from gummy bears and have students identify salt water versus water
    2. Pour off the solutions from agar tubes and have students identify the deeper penetration of malachite or permanganate
      1. Have the students plot the data and calculate the rates of osmosis
        1. This is extremely important as the third quantitative lab and emphasizes the Vision & Change Core Competency of Quantitative Reasoning.
        2. This is also a useful exercise for a lab report to emphasize the Vision & Change Core Competency of Communication

Curricular Notes

This unit covers the NSF Vision & Change Core Competencies:

  1. Quantitative Reasoning: graphing, surface area:volume
  2. Process of Science: hypothesis formation/observation
  3. Modeling and Simulation: simulations → mass, temperature, semi-permeable membrane

This unit covers the NSF Vision & Change Core Concept:

  1. Structure and Function: cellular membranes

This unit covers additional General Education competencies:

  1. Life-long Learning

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