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 (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?

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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!

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

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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.

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Sports Drinks!
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• 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.

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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.