Osmosis and Diffusion

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Osmosis and Diffusion

• Potato Lab

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What is 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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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 cups
• 1 teaspoon of salt
• Water
• Balance
• Marker to label cups

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Hypothesis

• Water Cup-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 Cup- 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

• Label one cup water. Label the other cup salt
  water.
• Measure the mass of a potato slice. Record the
  mass on a cup and place the slice in the cup.
  Repeat so that each cup has one potato slice.

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Procedure

• Add the same amount of water to each cup so that
  the potato slices are covered with water.
• Add 1 teaspoon of salt to the cup labeled salt
  water. Make sure that the salt dissolves.
• Let both cups sit at least overnight.

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Predictions

• What do expect to see on Monday?
• What will each potato feel like on Monday?
• What will each potato look like on Monday?
• What will happen to the mass of each potato when
  you measure it on Monday?

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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?