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
(Discussion Questions)
• What did we observe that would be
evidence of osmosis and diffusion?
• What did we measure to see if a change
takes place?
• What is the process that caused a change?
• What was the variable? What was 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!
• Can you drink
yourself to death??
• Should the tonicity
of a fluid
replacement drink
be isotonic,
hypertonic or
hypotonic???
Hypernatremia
•
•
•
Certain conditions may result in a decrease in the sodium concentration in
interstitial fluid. For instance, during sweating the skin excretes sodium as
well as water. If we replace the lost fluid with plain water then we may
produce a sodium deficit. The decrease in sodium concentration in the
interstitial fluid lowers the interstitial fluid osmotic pressure and establishes
an effective water concentration between the interstitial fluid and the
intracellular fluid. Water moves from the interstitial fluid into the cells,
producing two results that can be quite serious:
The first result, an increase in intracellular water concentration, called over
hydration which disrupts nerve cell function. In severe over hydration we
may see disoriented behaviour, convulsions, coma, and even death
The second result is a loss of interstitial fluid volume that leads to a decrease
in the interstitial fluid pressure. As the pressure drops, water moves out of
the plasma, resulting in a loss of blood volume that may lead to circulatory
shock.
Sports Drinks!
• Isotonic - quickly replaces fluids lost by sweating and supplies a
boost of carbohydrate. This drink is the choice for most athletes middle and long distance running or team sports. Glucose is the
body's preferred source of energy therefore it may be appropriate to
consume Isotonic drinks where the carbohydrate source is glucose in
a concentration of 6% to 8% - e.g. High Five, SiS Go, Boots Isotonic,
Lucozade Sport.
• Hypotonic - quickly replaces fluids lost by sweating. Suitable for
athletes who need fluid without the boost of carbohydrate e.g.
jockeys and gymnasts.
• Hypertonic - used to supplement daily carbohydrate intake normally
after exercise to top up muscle glycogen stores. In ultra distance
events, high levels of energy are required and Hypertonic drinks can
be taken during exercise to meet the energy demands. If used during
exercise Hypertonic drinks need to be used in conjunction with
Isotonic drinks to replace fluids.
Want to make your own?
• Isotonic - 200ml of orange squash (concentrated
orange), 1 litre of water and a pinch of salt (1g).
Mix all the ingredients together and keep chilled
• Hypotonic - 100ml of orange squash
(concentrated orange), 1 litre of water and a
pinch of salt (1g). Mix all the ingredients together
and keep chilled.
• Hypertonic - 400ml of orange squash
(concentrated orange), 1 litre of water and a
pinch of salt (1g). Mix all the ingredients together
and keep chilled.