Osmosis &
Diffusion
In Depth
-Potato Lab
Review of Osmosis and
Diffusion
• Osmosis is the movement of water across a
cell membrane from an area of higher
concentration to an area of lower
concentration.
• Diffusion is the movement of molecules
other than water across a membrane from
an area of higher concentration to and area
of lower concentration.
Water Potential
http://www.neosci.com/demos/101041_cell%20processes/Presentation.html
Getting the Info!
• Complete osmosis worksheet for
background info!
• Sodium/Potassium Pump and Osmosis…
• http://nutrition.jbpub.com/resources/animat
ions.cfm?id=27&debug=0
• Ion pumps worksheet!
Can a potato be used to demonstrate osmosis
and diffusion?
• Potatoes are composed of cells.
• Potato cells have cell membranes.
• Potato cells have some water and some salt
inside the cells.
Design the Experiment
• What can we observe that would be
evidence of osmosis and diffusion?
• What can we measure to see if a change
takes place?
• What is the process that will cause a
change?
• What is the variable? What is the control?
Materials
•
•
•
•
•
2 Potato slices
2 beakers
1 teaspoon of salt
Water
Balance
Hypothesis and Method
• Discuss a method with your group and
formulate a hypothesis!
Sample Data Box
Condition Initial Mass
Final Mass
Change in
mass
Texture change
Potato
in tap
water
Potato
in salt
water
Does osmosis explain the changes? Why?
Predictions
• What do expect to see tomorrow?
• What will each potato feel like on
tomorrow?
• What will each potato look like on
tomorrow?
• What will happen to the mass of each
potato when you measure it tomorrow?
Extension…Sports Drinks!
• Hypernatremia &
Hyponatremia
• Can you drink
yourself to death??
• Should the tonicity
of a fluid
replacement drink
be isotonic,
hypertonic or
hypotonic???
Lab Take-Up Slides
Hypothesis
• Distilled Water -Water will move from
the cup into the potato because water
outside the cell will be in higher
concentration than water inside the cell.
This is an example of hypotonic solution.
• Salt Water- Salt will move into the cell
from the cup and water will move out of
the cell into the cup because of a difference
in concentration. This is a hypertonic
solution.
Procedure
1. Label one beaker water. Label the other
beaker salt water.
2. Measure the mass of both potato slices.
Record the mass.
3. Add the same amount of water to each
beaker so that the potato slices are covered
with water.
Procedure
4. Add 1 teaspoon of salt to the beaker
labeled salt water. Make sure that the salt
dissolves.
5. Add slices and let both cups sit at least
overnight.
6. Measure the mass of each slice.
Sample Data for Quiz Review
Condition Initial Mass
Final Mass
Change in
mass
Texture change
Potato
in tap
water
12 grams
14 grams
+2 grams
More rigid,
firmer
Potato
in salt
water
11.5 grams
10 grams
-1.5 grams
Less rigid,
softer
Does osmosis explain the changes? Why?