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Lab 4
Diffusion and Osmosis
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
Concepts
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Selectively permeable membrane
Diffusion and osmosis
Hypertonic, isotonic, hypotonic
Water potential
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Water flows from high to low water potential
WP = PP + SP
PP = generally 0
SP = -iCRT
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I = how many particles it dissolves into (ionic 2 or more, molecular 1)
C = molarity
R = .0831
T = temp in Kelvin
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)
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?
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?
Procedure 3
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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?