Demonstration

LEARNING GOALS

By the end of this unit, you should be able to do the following: 1. Explain the difference between diffusion and osmosis. 2. Describe the relationship between a cell and a salt solution using the words hypotonic, hypertonic, and isotonic. 3. Predict whether a cell will shrivel, expand, or stay the same when submerged in a solution. 4. Use the correct vocabulary words to describe shriveling or expanding blood cells and plant cells. MATERIALS NEEDED 3 medium glass or clear plastic containers 3 drinking glasses or large cups 1 regular potato 2 leaves of fresh lettuce Italian Dressing knife ruler salt distilled water (sold with baby food or in the automotive section; “filtered” or “spring” water isn’t the same, only use distilled) measuring cups measuring spoons

Demonstration with a worksheet. You do not need to fill out an experiment tracking sheet for this lab. You must take pictures of the experiments for your worksheet. You must have a card with your name visible in the picture. OSMOSIS Potato Turgor Pressure (adapted from Michael Stone’s ENVS 1402L Lab Manual) You should take pictures on high power for your worksheet. Remember that plant cells placed in hypotonic (low solute) solutions will become stiff and those placed in hypertonic (high solute) solutions will become limp and wilted. 1. Add 2 1/2 cups of distilled water to a drinking glass. Label this “0% salt.” 2. Add 1 teaspoon of salt to 2 1/2 cups of distilled water in a drinking glass. Stir until dissolved. Label the glass “1% salt” with a piece of tape. (Save a small sample of this salt water for use in the next experiment as well.) 3. Add 2 teaspoons of salt to 2 1/2 cups of distilled water in a drinking glass. Stir and label “2% salt.” (Save a small sample of this salt water for use in the next experiment as well.) 4. Add 10 teaspoons of salt to 2 1/2 cups of distilled water in a drinking glass. Stir and label “10% salt.” (Save a small sample of this salt water for use in the next experiment as well 5. Cut out four rectangles of potato (no skin on any part of the rectangle). Make each rectangle 1 cm wide, 1 cm deep, and 5 cm long. 6. Gently bend a rectangle of each kind to see how stiff they start. 7. Place a rectangle potato into each of the four solutions. Wait 30 minutes. (At 25 minutes, cut out an extra rectangle of potato for comparison to the soaked potatoes.) 8. Compare each rectangle to the unsoaked potato. Is it more, less, or equally stiff? Conclusions – Which solutions were hypotonic, hypertonic, or isotonic to the potato? In your worksheet you are required to state which solutions were hypotonic, hypertonic, or isotonic based on the change in stiffness.

Wilting You should never put salad dressing (which is usually hypertonic to lettuce) on a salad that you want to eat several hours later. The demonstration below will show you why. You should take pictures for your worksheet. 1. In a medium container, add 2 teaspoons of salt to 2 1/2 cups of distilled water and mix. Label the container. 2. Add plain distilled water to the second container and a layer of Italian dressing to the third. Remember to shake the dressing first. It isn’t necessary to add a full 2 1/2 cups of dressing; use just enough to cover the lettuce leaf. 3. Add a fresh lettuce leaf to each container. Let sit one hour. How do you explain what happened? NEXT STEP The next item in the module is the worksheet. Paste your pictures into this sheet, answer the questions, and submit through the Assignment found in this module. Be prepared to answer quiz questions about osmosis and terms related to it.

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