DIFFUSION AND OSMOSIS
Experiment Set-Ups
8 groups: 4 small tables (4) + 2/each large table (2 = 4)
• DIFFUSION IN A COLLOID (ref. p4-6)
– 1 set-up per group
– Materials:
•
•
•
•
1 plate with agar
1 borer to make wells
Forceps or probe
1-2 drops of each liquid
– Methylene Blue
– Potassium Permanganate
Experimental Setups (2)
• OSMOSIS IN MODEL CELLS (ref. p.11-13)
– 1 set-up per group
– Materials:
• Damp paper towel “BED”: (Bottom to Top)
–Dry/Damp/MODEL CELLS/Damp
• Large Beaker filled with DI water
• Thread & Scissors
• 3 strips of plastic tubing
– SET UP ON NEXT SLIDE
Osmosis in Model Cells (2)
KEEP BAGS MOIST
• Create water-tight bags from plastic strips
– Each bag = model cell
• Twist, fold, twist, tie with thread
• Add ONE of the solutions: 1 pump (10ml)
– Bags must be flaccid, not turgid
• Weigh each model cell – record on Table
1, pg. 14 of Lab Manual
Set-Up Instructions
• Part of group sets up Diffusion in a
Colloid
• Other part sets up Osmosis in a Model
Cell
• Discuss starting Osmosis in a Model Cell
experiment simultaneously
PAUSE TO ALLOW SET-UPS
Principles of Diffusion
Definition:
• The natural tendency of particles to
move from areas of high
concentration to areas of lower
concentration
• Analysis on next 2 slides
Principles of Diffusion - 2
• Concentration
–Items per unit space
–Particles per unit volume
•Particle examples: atoms,
ions, molecules
Principles of Diffusion - 3
• Common examples of
Diffusion
–Cooking scents
–Perfume/cologne
Principles of Diffusion - 4
• Concentration Gradients
–Change in concentration from
one specific location to another
specific location
• Change can be gradual or abrupt
–Analogous to moving down a hill
Principles of Diffusion - 6
• Review Diffusion in a Colloid
Study Guide
– Data Collection & Analysis
Principles of Osmosis
DEFINITION
• A special case of Diffusion involving
H2O diffusing across a selectively
permeable membrane
• Next slide for analysis
Principles of Osmosis 2
• Selectively Permeable Membranes
–Membrane examples: plastic wrap,
Al foil, “thin films”
–Permeable: move across
–Selectively: structure of membrane
determines what materials
permeate it.
Principles of Osmosis 3
• Solutions
–Solvent
• Dissolver
• In Living Systems – always H2O
–Solute
• Material being dissolved
Principles of Osmosis 4
• Solutions as percentages of
solute
– 10% solution
• 10 units of solute
• 90 units of solvent
– Relate to solutions used in experiment
Principles of Osmosis 5
• Review Osmosis in a Model
Cell Study Guide
– Data Collection and Analysis
Osmosis in Living Cells
• Discuss differences between
Animal and Plant Cells
• Remind students to use
Homework answers during
experiment
• Review Set-up: next slide
3 scopes
RBC
3 scopes
RBC
3 scopes
RBC
3 scopes
RBC
SHARE DATA BETWEEN GROUPS
3 scopes
Elodea
3 scopes
Elodea
3 scopes
Elodea
3 scopes
Elodea
• Review will begin
promptly at 5:45pm
• BUDGET YOUR
TIME WISELY
Diffusion in a Colloid
Potassium Permanganate
Methylene Blue
150
374
Which molecule diffused
at a faster rate?
What is the relationship between
Molecular Weight & Diffusion Rate?
INVERSE
Osmosis in Model Cells
What happenedWhy
to the
What molecule
didModel
the water diffuse
into the caused the cells
Cells during the Model
60 minutes
to gain weight?
Cells??
H20
H20
H20
99% H20
1% Sucrose
100% H20
0% Sucrose
75% H20
25% Sucrose
Lower [water]
50% H20
50% Sucrose
Higher [solute]
Diffusion rate directly related
to the [solute] difference
Osmosis in Model Cells #2
YES – NET DIFFUSION WAS
INTO THE MODEL CELLS
DID ANY WATER DIFFUSE OUT
OF THE MODEL CELLS?
H20
?
YES
99% H20
1% Sucrose
100% H20
0% Sucrose
?
YES
?
YES
75% H20
25% Sucrose
50% H20
50% Sucrose
Sketch the Graph
50%
Weight
C
25%
B
A
Time
1%
Continuous & Discontinuous gradients
• Did the results from the Diffusion in a Colloid
experiment show a Continuous or
Discontinous Gradient
– CONTINUOUS
– Osmosis in Model Cell: DISCONTINUOUS
• What is necessary for a Discontinuous
Gradient to form?
– A Barrier to Diffusion
• Discuss Next
Week’s Lab