K-12 Teaching and Learning From the UNC School of Education

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Learning outcomes

Students will:

  • Hypothesize about experiments in the laboratory.
  • Understand and draw the structure and function of the cell membrane.
  • Understand and describe the movement of particles across the cell membrane.
  • Explain the difference between hypertonic, hypotonic, and isotonic solutions and how cells react in each of these solutions.
  • Observe living tissue undergoing diffusion and osmosis.

Teacher planning

Time required for lesson

90 minutes

Materials/resources

  • potatoes
  • water
  • ten percent salt solution
  • microscope slides
  • coverslips
  • microscopes
  • red onion
  • plastic sandwich bags
  • dental floss
  • disposable cups
  • masking tape
  • electronic balance or triple beam balance
  • iodine
  • graduated cylinder
  • starch solution

Pre-activities

  • The students should be able to understand the basic function of the cell membrane.
  • The students should be able to use the microscope and make a wet mount with ease.
  • The student should be able to use the steps of scientific research and observation.

Activities

Due to turgor pressure, plant tissue is normally rigid. What happens to plant tissue if it is exposed to a hypertonic and hypotonic solutions?

Part A—the potato cell

  1. Label two cups with your group’s names. On one cup write “salt solution” and on the other write “plain water.” Use masking tape for your labels.
  2. Obtain two slices of potato that are approximately the same size. Using a balance, find the individual masses of each potato slice and record in a table. (Each student should design an appropriate table.) Put the first potato slice in the salt solution cup and cover it with salt water. Put the second potato slice in the plain water and cover it with plain water.
  3. Now write your hypothesis: Predict what you think is going to happen to each potato slice. Write down your hypothesis.
  4. Leave the potato slice in the solution overnight.
  5. On the following class day, carefully blot off any excess water, and mass each potato slice. Record the masses in your data table.
  6. Find the percent change in mass = (final mass − initial mass)/(initial mass).
  7. Record your percent change in mass on your data table.
  8. Describe what happened to the cells after being exposed to hypertonic (salt) and hypotonic (plain water) solutions. Use in your explanations the following terms correctly: hypertonic, hypotonic, turgor pressure, wilting, plasmolysis, and osmosis.
  9. What was the independent variable in this experiment?
  10. What was the dependent variable?
  11. What was the control?
  12. Did your data support your hypothesis? Explain citing your data.
  13. What conclusions can you draw from this lab?

Part B—Are plastic bags selectively permeable?

  1. Will the polyethylene membrane allow the iodine to cross the membrane?
  2. Will the polyethylene membrane allow starch, large molecules, to cross the membrane?
  3. Make a hypothesis.
  4. Objective: In this experiment you will determine whether diffusion occurs across a plastic membrane.
  5. Measure twenty milliliters of starch solution into a graduated cylinder. Pour the starch solution into a plastic bag and use dental floss to tie it together.
  6. Fill a cup halfway with water. Add ten drops of iodine to the water in the cup before you put the bag and the water in the cup below. Record the colors of each, the bag and the cup, in a data table. Set the cup aside for thirty minutes.
  7. After thirty minutes, record the colors of the bag and the cup into your second data table.
  8. Did iodine molecules move through the membrane? Explain how you know.
  9. Did starch molecules pass through the membrane? Explain how you know.
  10. Does your data support your hypothesis? Explain why or why not.
  11. What can you infer from this experiment about the movement of large and small molecules through a thin polyethylene membrane?

Part C—Plasmolysis of a plant cell

  1. Make a wet mount of red onion skin.
  2. Observe the cell on low power and then on high power. On your data sheet, draw a cell and its contents. Include magnification and a few observations.
  3. Place a drop of salt solution on one side of the coverslip. Place a piece of paper towel on the opposite side of the coverslip to draw the salt solution over the onion cells.
  4. Observe the leaf on low power (100× magnification). Wait a few minutes. Draw the cell and its contents. Include a few observations.
  5. Write a paragraph explanation using the same terms in part A #8.

Assessment

Possible assessment techniques:

  • Formal lab report using each part of the scientific method.
  • Quiz students using other examples of membrane permeability.
  • Have the students design and carry out another experiment using permeability.

Supplemental information

I use Glenco, Biology to back up my teaching in the classroom.

Independence High School adopted a great review book called Reviewing Biology that has helped tremendously on our E.O.C. scores. (This book is published by Amsco.)

Comments

I have also used each part (A, B, C) separately as a mini lab for the three to five days that I teach membranes and permeability. I also would like to give credit to Sarah Gnilka of East Mecklenberg High School for her ideas in this lesson.

  • Common Core State Standards
    • English Language Arts (2010)
      • Science & Technical Subjects

        • Grades 11-12
          • 11-12.LS.3 Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.
        • Grades 9-10
          • 9-10.LS.3 Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.

  • North Carolina Essential Standards
    • Science (2010)
      • Biology

        • Bio.1.1 Understand the relationship between the structures and functions of cells and their organelles. Bio.1.1.1 Summarize the structure and function of organelles in eukaryotic cells (including: the nucleus, plasma membrane, cell wall, mitochondria, vacuoles,...
        • Bio.1.2 Analyze the cell as a living system. Bio.1.2.1 Explain how homeostasis is maintained in the cell and within an organism in various environments (including: temperature and pH). Bio.1.2.2 Analyze how cells grow and reproduce in terms of interphase,...

North Carolina curriculum alignment

Science (2005)

Grade 9–12 — AP Biology

  • Goal 1: The learner will develop abilities necessary to do and understand scientific inquiry.
    • Objective 1.02: Design and conduct scientific investigations to answer biological questions.
      • Create testable hypotheses.
      • Identify variables.
      • Use a control or comparison group when appropriate.
      • Select and use appropriate measurement tools.
      • Collect and record data.
      • Organize data into charts and graphs.
      • Analyze and interpret data.
      • Communicate findings.
    • Objective 1.03: Formulate and revise scientific explanations and models using logic and evidence to:
      • Explain observations.
      • Make inferences and predictions.
      • Explain the relationship between evidence and explanation.
  • Goal 2: The learner will develop an understanding of cells as the structural and functional units of life.
    • Objective 2.02: Analyze cellular membranes.
      • Structure and function.
      • Variations.
      • Investigate mechanisms of transport.
      • Recommended laboratory - Diffusion and Osmosis

Grade 9–12 — Biology

  • Goal 1: The learner will develop abilities necessary to do and understand scientific inquiry.
    • Objective 1.02: Design and conduct scientific investigations to answer biological questions.
      • Create testable hypotheses
      • Identify variables.
      • Use a control or comparison group when appropriate.
      • Select and use appropriate measurement tools.
      • Collect and record data.
      • Organize data into charts and graphs.
      • Analyze and interpret data.
      • Communicate findings.
    • Objective 1.03: Formulate and revise scientific explanations and models of biological phenomena using logic and evidence to:
      • Explain observations.
      • Make inferences and predictions.
      • Explain the relationship between evidence and explanation.
  • Goal 2: The learner will develop an understanding of the physical, chemical and cellular basis of life.
    • Objective 2.03: Investigate and analyze the cell as a living system including:
      • Maintenance of homeostasis.
      • Movement of materials into and out of cells.
      • Energy use and release in biochemical reactions.