Cell%20Membranes

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Cell Membranes

• Diffusion and Osmosis

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Cell Membrane

• Lipid Bilayer
• Selectively permeable- some substance can cross
  although others cannot
• Provides protection and support

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Cell Walls

• Found in plants, fungi, algae, and nearly all
  prokaryotes
• Outside the cell membrane
• Add extra support/protection

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Diffusion

• Every living cell has a liquid interior
  (Cytoplasm) and a liquid exterior
• It is separated by at least the cell membrane
• Most of the liquids are solutions and have a
  concentration
• Example 15 grams of salt in 3 liters of water
  would have a concentration of 5 g/l

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Diffusion cont..

• Concentrations want to be equal wherever they are
• Move from areas of high concentration to areas of
  low concentration until they are equal
• www.biosci.ohiou.edu/introbioslab/.../diffusion/Di
  ffusion.html

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Diffusion in cell membranes

• Movement of materials across a cell membrane
• Move from High ? Low concentration until they are
  in equal
• DOES NOT require a cell to use energy

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Osmosis

• Diffusion of water through a semi-permeable
  membrane

Were NOT talking About Osmosis Jones
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Osmosis
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Osmotic pressure

• Some cells can absorb a lot of water
• This can cause a cell to swell and rupture

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Osmotic Pressure Continued

• What Happens when a cell is placed in a hypotonic
  solution?

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Facilitated Diffusion

• Large molecules cannot move right across the cell
  membrane must go through channels
• Does not require energy

Glucose molecules
High Concentration
Cell Membrane
Low Concentration
Protein channel
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Active transport

• If a material moves against the concentration
  difference
• (Low ? High)
• Requires ENERGY.

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Endocytosis

• when the cytoplasm and membrane fold around
  material, creating a vacuole inside the cell
• Two types
• Phagocytosis solid materials taken in (Cell
  Eating)
• Pinocytosis liquid is taken in (Cell Drinking)

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Exocytosis

• when the contents of a cell are forced out.
• The vacuole is fused with the cell membrane and
  forced out.