1. Tonicity Diagrams

2. Understanding Diagrams
There are three simple steps to help you figure out diagrams that deal with diffusion and osmosis.
1. Check to see if they have specified what can pass through the semi-permeable membrane.
*If they haven’t specified, assume that only water can pass through.
2. Determine the solute concentration in the two solutions present.
3. Determine the direction the substance must move to meet equilibrium.

3. Understanding Diagrams
This is a model of a cell in solution.
They tell you that the baggie is permeable to water only. What does that mean?
It means only water can pass through the bag.
If the solution outside the bag is 95% water, how much solute is in the solution?
If the solution inside the bag is 98% water, how much solute is inside the bag?
Which direction does water move?
Towards the area with more solute
Out of the bag!
5% solute
2% solute 5% 2%

4. Understanding Diagrams
In this diagram, we can measure the amount of water moving through the membrane by looking at the height of the water in the glass tube!
If water moves into the bag, the water in the tube will ______.
If water moves out of the bag, the water in the tube will ______.
What do they mean when they say “starch solution?”
Write a situation for this diagram that would make the water in the tube rise.
This simply means starch mixed with water. So starch is the solute.
rise
fall

5. Understanding Diagrams
Distilled water has no solute. It’s 100% water.
What does this mean? ?
This diagram looks a little funny, but all the same rules apply!
You still have a semi-permeable membrane.
Water is still going to pass through the membrane towards the area with higher solute to try to reach equilibrium.

6. Let’s Practice!
You will be given various scenarios. For each of the scenarios: 1. Draw the set-up for the scenario. 2. Label the semi-permeable membrane. 3. Label the solutions with % solute. 4. Draw arrows to show the direction of water movement. 5. Write a description of the movement of water.

7. Let’s Try One!  
A cell containing a 5% salt solution is placed in a beaker of 10 % salt solution.
Scenario
Diagram
Explanation
Example:
A cell containing a 5% salt solution is placed in a beaker of 10 % salt solution.