Activity: A Model of Osmosis (Cucumbers Fresh and Pickled)

Goals:

  1. To observe the process of osmosis in action.
  2. To discuss the implications of osmosis in everyday life.

Background Information: People have been utilizing the process of diffusion and osmosis in their everyday lives since ancient times. When our ancient ancestors salted meat and fish, they were removing water from the cells of the muscle tissue of animals used for food in order to prevent spoilage. We know now that bacteria and molds do not grow easily without water. Since cells are mostly water, removing it kept bacteria and molds from spoiling most meat and fish.

We also know that it’s easy to keep lettuce crisp in the supermarket by misting it from time to time with water from a sprinkler. More water on the outside of the lettuce cells gives the cells the opportunity to take in additional water. Full cells equal crisp lettuce. Pickling is another way to preserve food. What happens to a cucumber in the process of becoming a pickle?

Materials: slices of cucumber, salt, two plastic tumblers, water, wax pencil, paper towels

Procedure:

  1. What I Know: Write a sentence or two about what you already know about the process of osmosis.
  1. You will need two plastic tumblers. Using a wax pencil label one tumbler Fresh Waterand the other Salt Water.
  2. Fill the Fresh Watercup with plain water and fill theSalt Watercup with the salt solution.
  3. Add a cucumber slice to each of the cups and set them aside for about 10 minutes.
  4. Take the cucumber slice out of the salty water first. Notice how it feels. Try to bend it.
  5. Take the cucumber out of the fresh water. Notice how it feels in comparison with the cucumber in the salty water. Try to bend it.
  6. What I Did: Write a short description of the procedure you used in this activity.
  1. What I Observed: Draw an illustration of the cucumber slices in fresh water set-up and cucumber slices in salt water set up. Write a short description of each of your cucumber observations.
  2. Illustration of cucumber-water set up with labels:
  1. Description of salt water cucumber:
  1. Description of fresh water cucumber:
  1. What I Learned: Write a short summary of what you learned about osmosis from doing this activity and relate it to the pickling process that is used to preserve foods.
  1. What I Wonder: Pose a why or how question related to this activity that you may still wonder about.
  1. Questions: Answer the following questions as complete statements.
  1. In which cucumber slice did water move into the cucumber cells? Explain why this happened. Draw a diagram with arrows to illustrate the movement of water.
  1. In which container did water move out of the cucumber cells? Explain why this happened. Draw a diagram to illustrate the movement of water.
  1. How does pickling keep foods edible for long periods of time?