3.4 Diffusion and Osmosis

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3.4 Diffusion and Osmosis

• LEQ How does passive transport move chemicals
  across a cell membrane?
• Reading 3.5, 3.2 (focus on organelles with
  membranes)
• Quiz friday
• Journal
• Think of several features and parts of membranes
  necessary for them to function correctly and then
  write an entry detailing how changing them could
  cause a membrane to function poorly.
• Key terms diffusion, osmosis, passive transport

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3.4 Diffusion and Osmosis
Diffusion is the random movement of particles in
a solution.

• All molecules and atoms are in constant motion
• Energy
• Collision
• Heat (thermal energy)
• Diffusion applet (see screen)
• 3 general types of passive transport

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• Journal prompt Have you ever been stuck in
  crowd? A cramped elevator or a packed concert
  can cause certain responses in people. Describe
  how people might feel in a crowded space.
• Construct an analogy to explain why molecules
  diffuse from high to low concentrations using
  crowds.

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3.4 Diffusion and Osmosis
Materials move across membranes because of
concentration differences.

• Passive Transport
• Powered by random atomic molecular movement
• No energy requirements

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3.4 Diffusion and Osmosis
1) Some chemicals can move across the cell
membrane by simple diffusion.

• Diffusion gradients
• Differences in concentration
• Net movement
• high ? low
• small, nonpolar solutes
• O2, CO2, steroids

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3.4 Diffusion and Osmosis
2) Many solutes can only pass across a membrane
through facilitated diffusion.

• Facilitated diffusion moves chemicals through
  specialized transport proteins
• Small or large
• Polar, Ionic
• Regulation
• Size/shape restricted
• gates

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3.4 Diffusion and Osmosis

• 3) Osmosis is the net movement of water in
  response to solute concentrations and pressure

• Cells are sensitive to changes in solutions
• Water diffuses down concentration gradients
• Weakly via simple diffusion
• Facilitated
• aquaporins

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3.4 Diffusion and Osmosis

• normalcy for animal cells
• equilibrium

• expansion
• cell death (lysis)

• Crenation (wrinkling)
• dysfunctional

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Summary

• Explain what a concentration gradient is and what
  it means for a molecule to diffuse down its
  concentration gradient
• Explain why facilitated diffusion does not
  require energy from a cell
• A cell is bathed in fluid. However, you notice
  that water is flowing out of the cell. In what
  kind of solution is this cell immersed isotonic,
  hypotonic, or hypertonic?
• How are receptors and transport proteins similar?

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Answers

• A concentration gradient is the difference in
  concentration of a substance from one location to
  another. A molecule diffuses down its
  concentration gradient by moving from one region
  of higher concentration to a region of lower
  concentration.
• No energy is needed because the molecules move
  down an concentration gradient
• Hypertonic
• Both are proteins and may work with only specific
  molecules. In addition, both may require a
  change in shape to accomplish their function.