Grade:
Time:
Topic:
Concept:
SOL:Science:
Rationale:
Goals:
Objective:
Osmosis is the natural passage or diffusion of water (or other liquids) through a semi-permeable membrane.
Materials:
- Lettuce
- Salt
- Water
- Two Identical Bowls
Procedure:
- Fill two identical dishes with water.
- Tear off two big pieces of lettuce (they should be about the same thickness and color).
- Add two tablespoons of salt to one of the dishes.
- Put one leaf in the plain water dish.
- Put the other leaf in the dish that contains the salt water.
- Let the leaves soak for 20 minutes.
- Compare the leaves. Physically remove them from the water with a spoon and hold the lettuce up. Do you notice any difference between the two? The lettuce that had been submerged in the salt water should be very limp.
Why?
Through osmosis, water naturally moves from areas of low salt concentrations to areas of high salt concentrations. Adding salt to the water creates a higher salt concentration in the water in the dish than in the water contained in the lettuce. Consequently, the water in a leaf of lettuce that is soaking in salt water will migrate out of the lettuce leaving a mushy leaf behind.