7th Grade
Name_______________________
Title: Osmosis Lab
If you need to do this at home, use a scale to find the weight of the
potatoes.
Introduction: Cells must be able to allow substances to travel through their cell
membranes. Gases and nutrients must go into the cell, waste gases and waste
products must go out. Diffusion is the movement of substances from high to low
concentrations. Osmosis is diffusion of water through a membrane. Since cells
are surrounded by membranes, we will use the term osmosis to describe the
movement of substances across cell membranes. Membranes are able to block
the movement of some substances. Salt does not move freely across cell
membranes. In this activity you will see the reaction of cells to salt water.
Materials: salt water, potatoes, balance, beakers, tap water, distilled water
Procedure:
1. Weigh 3 slices of potato. Write down what they weigh.
2. Place 1 potato in the salt water solution, the second in the tap water solution,
and the third in the pure water solution.
3. After 20 mins take the potatoes out of the salt water and blot dry. Weigh
again.
Prediction: What will happen to the weight of the potatoes?
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Data:
Salt
Tap H2O
Pure H2O
1. Starting weight of potatoes…… ________g _________g ________g
2. Ending weight of potatoes…….. ________g _________g ________g
3. Change…… …………………… ________g _________g ________g
Analysis:
1. What happened to the weight of the potatoes?
2. Why did this occur?
3. Did water or salt move across the cell membrane?
4. Draw a diagram of what you think happened to the potato cells. Show the salt
as black dots.
5. Why might cells keep some substances from entering the cell?
6. Why was the tap water different than the pure water? Explain.
Conclusion: (5 sentences)