Hocus Pocus Osmosis

GRADE: 8

CLUSTER: Cells, Tissues, Organs, and Systems

TIME: 1 hour

SPECIFIC LEARNING OUTCOMES

KEY WORDS

Osmosis, Cells, Experiment

Objective:

To demonstrate, by experimentation, how all living cells absorb and exchange liquids through the process of osmosis.

Teacher Materials:

Student Materials: (per group)

Experiment 1:
Through the Water Glass 		Experiment 2:
The Cup Runeth Over
  • 1 Piece Parchment Paper
  • Glass of Water
  • 5 mL Salt
  • Elastic Band
  • Shallow Pan of Water strongly coloured with Vegetable Dye
  • Experiment 1 Information Sheet

Procedure:

EXPERIMENT 1

  1. Begin with a brief introduction to the process of osmosis. Explain that the class will be conducting two different experiments to demonstrate the process.

  2. In groups of 3-4, ask the students to prepare for the experiment by completing the Title and Apparatus portion of the Experiment # 1 Information Sheet.

  3. Write the following Procedure portion of the experiment on the board, and ask the students to copy the steps onto their Information Sheet.
    1. Dissolve 5 mL of salt in the glass of water.
    2. Cover the top of the glass of water with the parchment paper.
    3. Place the elastic band over the parchment paper and seal tightly.
    4. Place the glass of water upside down in the shallow pan of dyed water.
    5. Observe

  4. Once the Procedure portion of the experiment has been copied onto their Information Sheet, allow the students to conduct the experiment.

  5. Have the students complete the Observations section of the sheet, making note of the length of time necessary for the water in the glass to become evenly coloured.

  6. Using the large sheet of graph paper, graph the time required for the glass of water in each group to become evenly coloured from the dye.

  7. Allow some time for a class discussion. Have the students suggest reasons for the following questions:
    1. Why did the water change colour?
    2. What factors could have affected the differences in the length of time necessary for the water in the glass to change colour?
    3. What can we conclude from this experiment?

  8. Have the students complete the Conclusion portion of the Information Sheet. Summarize the experiment by concluding that the tiny particles of water and dye passed through the invisible pores in the parchment paper. This exchange of liquids through a permeable membrane is called osmosis. All living cells are surrounded by such a membrane, and absorb water and dissolved substances in this way.
EXPERIMENT 2

  1. In groups of 3-4, ask the students to prepare for the experiment by completing the Title and Apparatus portion of the Experiment 2 Information Sheet.

  2. Write the following Procedure portion of the experiment on the board, and ask the students to copy the steps onto their Information Sheet.
    1. Fill the empty wine glass with 175-200g dried peas (until almost overflowing)
    2. Pour water over the dried peas (enough to fill to the brim)
    3. Gently place the glass onto an inverted metal pot lid
    4. Observe

  3. Once the Procedure portion of the experiment has been copied onto their Information Sheet, allow the students to conduct the experiment.

  4. Have the students complete the Observations section of the sheet, making note of the length of time necessary for the pea heap to rise and begin to overflow.

  5. Using the large sheet of graph paper, graph the time required for the pea heap in each group to rise and overflow.

  6. Allow some time for a class discussion. Have the students suggest reasons for the following questions:
    1. Why did the pea heap rise?
    2. What factors could have affected the differences in the length of time necessary for the pea heap to rise and overflow?
    3. What can we conclude from this experiment?

  7. Have the students complete the Conclusion portion of the Information Sheet. Summarize the experiment by concluding that the water penetrated through the walls of the pea cells, rehydrating the cells. The pressure formed from the swelling cells made the peas swell and flow over the sides of the glass. This is how plants and animals take in water for life.

Assessment:

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