1. Lab 4
Diffusion and Osmosis

2. Purpose Learning Objectives
• To investigate the relationship among surface area, volume, and the rate of diffusion
• To design experiments to measure the rate of osmosis in a model system
• To investigate osmosis in plant cells
• To design an experiment to measure water potential in plant cells
• To analyze the data collected in the experiments and make predictions about
molecular movement through cellular membranes
• To work collaboratively to design experiments and analyze results
• To connect the concepts of diffusion and osmosis to the cell structure and function

3. Concepts Selectively permeable membrane Diffusion and osmosis
Hypertonic, isotonic, hypotonic
Water potential
Water flows from high to low water potential
WP = PP + SP
PP = generally 0
SP = -iCRT
I = how many particles it dissolves into (ionic 2 or more, molecular 1)
C = molarity
R = .0831
T = temp in Kelvin

4. 3 Parts
Part 1: Use artificial cells to study relationship of surface area to volume
Part 2: Create models of living cells to explore osmosis and diffusion
Part 3: Explore osmosis in living cells (Elodea)

5. Procedure 1 1. Test phenolphthalein color change
2. Cut out different cell sizes
3. Put the cells into acid or base to test how far the color change will penetrate
How will you know what the best cell size ratio is?

6. Procedure 2 Use dialysis tubing as a semipermeable membrane
Use different solutions (sucrose, glucose, NaCl, albumin protein, pure water) inside the “cell” and outside the cell
Observe the changes that happen in the tubing… what will we measure?
What will this show?
Design Your Own Experiment (DYOE!)
What else can you test about osmosis and diffusion?

7. Procedure 3 Use Elodea plant to test osmosis
Draw the normal cell appearance under a microscope
Predict what one of the solutions in part 2 would do the cells
Test one of the solutions from part 2 on your plant cells and redraw the plant cells to see if you were right!
DYOE!
Use potatoes, determine the unknown molarities of the sucrose beakers… how?