Click for a copy of the Google Doc version of the handout that goes with this virtual lab.


What follows is a video version of an osmosis lab that uses thistle tubes.

Key concepts/terms covered in this lab include

  • diffusion
  • osmosis
  • hypotonic, hypertonic, and isotonic
  • concentration gradient
  • osmotic pressure.

In addition to thistle tubes and sucrose solutions of various molarities, the lab uses dialysis tubing:  an artificial selectively permeable membrane that is permeable to water, but not to sucrose.

Part 1: The Setup, and Your Initial Explanation

Watch the first 25 seconds of the video.

Your initial explanation

Do your best responding to the two questions posed in the introduction. Don’t worry if you don’t know the answer. Your initial speculation will make it much easier to learn what’s to come. So write down your answers: 

    1. Why is water rising up the thistle tubes?
    2. Why is water rising more in some thistle tubes than others.

Part 2: Understanding the science

Watch the video from 1:14 until 5:51.

Discussion Questions

Working in pairs (or larger groups, depending on your teacher’s preferences) explain the rise of the fluid in the thistle tubes by discussing the questions below. Each question is a variation of the one before: you’re just using different concepts to explain what happened.

  1. Explanation 1: Explain the rise of the fluid in the thistle tube in terms of diffusion of water. 
  2. Explanation 2: Explain the rise of the fluid in the thistle tube in terms of hypotonic and hypertonic solutions.
  3. Explanation 3: Explain the rise of the fluid in the thistle tube in terms of osmotic pressure.

Writing it down

After you’ve discussed these questions, write out a complete explanation.

Using terms like osmosis, hypotonic, hypertonic, osmotic pressure, and concentration gradient, explain

  1. Why the water level in the tubes is rising?
  2. Why, in the same period of time, there’s more movement in some of the tubes than others?


Part 3: Deepening your understanding, and applying what you’ve learned

Now watch the last part of the video.

Writing it down

After watching the last part of the video, write out your answers to the following questions.

  1. Using your osmosis vocabulary, explain why the water level doesn’t rise in the 0.0 M thistle tube.
  2. Use the concept of concentration gradient to explain the difference in the movement of fluid into the thistle tubes.
  3. Explain how osmosis affects animal cells in hypotonic, isotonic, and hypertonic environments
  4. Explain how osmosis affects plant cells in hypotonic, isotonic, and hypertonic environments. What’s plasmolysis? Why do plants wilt
  5. How do plant roots crack sidewalk pavement?