Osmosis

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Osmosis DiffusionIn Depth

• -Potato Lab

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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.

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Water Potential
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http//www.neosci.com/demos/10-1041_cell20process
es/Presentation.html
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Getting the Info!

• Complete osmosis worksheet for background info!
• Sodium/Potassium Pump and Osmosis
• http//nutrition.jbpub.com/resources/animations.cf
  m?id27debug0
• Ion pumps worksheet!

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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.

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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?

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Materials

• 2 Potato slices
• 2 beakers
• 1 teaspoon of salt
• Water
• Balance

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Hypothesis and Method

• Discuss a method with your group and formulate a
  hypothesis!

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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?
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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?

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ExtensionSports Drinks!

• Hypernatremia Hyponatremia
• Can you drink yourself to death??
• Should the tonicity of a fluid replacement drink
  be isotonic, hypertonic or hypotonic???

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Lab Take-Up Slides
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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.

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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.

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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.

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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?