Name: ______________________ Date: ________ Class: ______
Under What Conditions Does Osmosis Occur?
Osmosis is the diffusion of water through a selectively permeable
membrane. There are three possibilities for the direction of water
1.) Water moves out; when water diffuses out of the cell, the
cell shrinks, (weight loss). The solution responsible for this
loss is called a hypertonic solution, which has a lower free
water molecule concentration than the inside of the cell.
2.) Water moves in; when water diffuses into the cell, the cell
swells, (weight gain). The solution responsible for this gain
is called a hypotonic solution, which has a higher free water
molecule concentration than inside the cell.
3.) No net water movement; when water diffuses into and out
of the cell at equal rates, the cell stays the same size,
(equilibrium). The solution responsible for this equilibrium is
called an isotonic solution, which has the same free water
molecule concentration as the inside of the cell.
You can observe the movement of water into or out of a grape under
3 small jars
3 saran wrap pieces large enough to fit over top of jars
3 rubber bands to hold saran wrap around lid
1 saturated salt water solution (in a pitcher)
masking tape for labels
1. Fill and label one jar with grape juice.
2. Fill and label a second jar with salt water solution.
3. Fill and label the third jar with tap water.
4. Using an electric balance, find the mass of the first grape and
place the grape into the grape juice jar, covering it with saran wrap
and placing the rubber band around the lid to seal it. Record this
grape’s mass in table 1 – 1, under Original Mass.
5. Repeat step 4 for the final two grapes and their solutions.
6. Once the experiment is set up, set the jars aside making sure you
put your initials and class period on the masking tape used to label
the solutions so you can find it tomorrow. It will now sit for 40
7. Predict whether the mass of the grape will increase or decrease
over the next 40 minutes. Record this prediction in Table 1 – 1,
under Predicted Mass. Explain why you predicted this.
8. After 40 minutes, remove each grape from its jar, and dry it
gently with a paper towel. Using the electric balance, find its mass
again. Record your results in Table 1 – 1, under Actual Mass.
9. Clean up your materials.
TABLE 1 – 1
Solution Original Mass Predicted Explain why Actual Mass
Mass the predicted
1. List the solutions in which osmosis occurred.
2. How did you determine whether osmosis occurred in each of the three
3. After noting the change in each of the grapes masses, label each
solution as hypertonic, hypotonic, or isotonic.