Diffusion Iodine and Starch Reaction

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Diffusion Iodine and Starch Reaction

• http//www.youtube.com/watch?v2Th0PuORsWYfeature
  related

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1. What caused the color change you observed?

• Starch solution inside the dialysis tubing
• Water outside the dialysis tubing
• Iodine added to the water
• --- REACTION! Color change! ? How?

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2. What was able to diffuse across the membrane?

• Starch solution changed color
• Water in the beaker didnt have a reaction
• What can you conclude
• About the movement of starch molecules?
• About the movement of iodine molecules?
• About the movement of water molecules?

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What molecules were able to diffuse in/out the
membrane?

• Water
• Iodine
• Why couldntstarch move acrossthe membrane?

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3. Was the beaker of water hypertonic or
hypotonic compared to the starch solution in the
tubing?

• Hypertonic more solute (high concentration)
• Hypotonic less solute (low concentration)
• Whats a solute? The substance youre
  dissolving (starch)
• Whats a solvent? The substance youre
  dissolving the solute IN (water)

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3. Where is the highest concentration of solute?
The lowest concentration?
Hypertonic
Hypotonic
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4. Why was the weight of your tubing different
after adding iodine to the water?

• Water moves from high ? low concentration
• Water moved into the dialysis tubing due to
  OSMOSIS!
• Would water still move across the membrane
  without using iodine?

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How does the tubing represent a cell membrane?

• Selectively (semi) permeable only certain
  molecules can cross the membrane
• Water, iodine, NOT starch
• Normally, cells exist in isotonic solution
• Whats isotonic? Whats the solution?
• Osmosis can cause cells to shrivel up, swell, or
  even burst!

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How can water cause a cell to burst?

• When cells are in a freshwater solution
• Water rushes in, bursting the cell

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What about plant cells?

• What do plant cells have that animal cells do
  not?
• Notice the cell wall does not collapse (or
  burst), but the cell membrane can collapse

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What allows water molecules in/out of the cell?

• Aquaporins water channel proteins
• Type of facilitated diffusion, because it
  requires help from a specific channel protein
• Special protein channels are embedded in the
  lipid bilayer a double-layered sheet that forms
  a strong, flexible barrier called the
• YOU GUESS IT! CELL MEMBRANE!

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The Lipid Bilayer
Protein channel
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2 sheets of lipids make the lipid bilayer
-- PHOBIC hating
-- PHILIC loving
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Why is the hydrophilic portion on the outside and
the hydrophobic portion on the inside of the two
sheets?
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Recap -

• Osmosis is movement of WATER molecules from high
  to low concentration
• This creates osmotic pressure - a force produced
  by the net movement of water

• Diffusion is movement of molecules from high to
  low concentration

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Types of Transport

• ACTIVE TRANSPORT
• Moves materials against concentration gradient
• Requires energy!
• Endocytosis - import
• Phagocytosis
• Exocytosis - export

• PASSIVE TRANSPORT
• Occurs due to concentration gradient
• Requires no energy
• Diffusion
• Osmosis