The Cell Membrane

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The Cell Membrane
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What is a membrane?

• A membrane is a device that selectively permits
  the separation of one or more materials from a
  liquid or gas.

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Passive Transport

• The transport of substances through the cell
  membrane without using energy.

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• Now there are two different ways to transport
  material through the cell membrane WITHOUT using
  energy
• Diffusion and Osmosis

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Diffusion

• The process of moving from areas of high
  concentration to areas of low concentration

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Diffusion Demonstration Model

• Molecules are always in motion
• In a closed system the molecules evenly try to
  distribute
• Which results in a the initial movement of
  molecules from high to low concentrations
• Once an equilibrium is reached there is no net
  movement of molecule.

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• What is separating the two different types of
  beads?
• How do the two volumes compare in this model?
• Which side of the model has a higher
  concentration of beads?
• How is diffusion going to take place?
• What happens with continued shaking?
• Is equilibrium reached? (Has homeostasis been
  reached?)

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Add Homeostasis

• is the maintenance of a stable internal
  environment.

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Dialysis

• Its a process that separates solvents from
  blood. Such as removing glucose or fats with out
  removing the important molecules that our blood
  needs.
• The tubing used in semi-permeable. Meaning some
  material can pass through and other cannot.

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Osmosis
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Osmosis

• The diffusion of water from areas of high
  concentration to areas of low concentration
  through a semi-permeable membrane.

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• Water moves from a high concentration of water
  (less salt or sugar dissolved in it) to a low
  concentration of water (more salt or sugar
  dissolved in it).  This means that water would
  cross a selectively permeable membrane from a
  dilute solution (less dissolved in it) to a
  concentrated solution (more dissolved in it).

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• Water can cross the cell membrane through the
  lipid bi-layer and with special proteins. If
  enough water enters the cell by osmosis, the cell
  can swell enough to burst open and die.  This is
  demonstrated in the picture.

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• In this picture a red blood cell is put in a
  glass of distilled water (all water with no salt
  or sugar in it).  Because there is a higher
  concentration of water outside the cell, water
  enters the cell by OSMOSIS.  In this case too
  much water enters and the cell swells to the
  point of bursting open.  In the end pieces of
  cell membrane are left in the water. 

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Osmosis Cont.

• The concentration (amount) of all substances
  affects the movement of materials in and out of
  the cell.

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Hypotonic

• Solute concentration contains a low
  concentration of solute
• Water concentration contains a high
  concentration of water
• Water movement water diffuses into the cell
• Effect on the cell causing the cell to swell and
  possible explode

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Cells in hypotonic solution
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Draw a picture
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Isotonic

• Solute concentration is equal to the water
  concentration
• Water concentration is equal to the solute
  concentration
• Water movement equal diffusion (water diffuses
  into and out of the cell at equal rate)
• Effect on cell none

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Normal cells in isotonic solution
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Draw a picture of an isotonic solution next to
the definition
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Hypertonic

• Solute concentration contains a high
  concentration of solute
• Water concentration contains a low concentration
  of water
• Water movement water diffuses out of the cell
• Effect on the cell causing the cell to shrivel

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Cells in hypertonic solution
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Draw a picture next to the definition
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Quiz yourself

• 1 2 3

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Active transport
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Active transport

• The transport of molecules from areas of high to
  low concentration with the use of energy.
• The cell energy is the ATP made in the
  mitochondria.

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Bulk movement of substances across the membrane

• Endocytosis
• Phagocytosis
• Pinocytosis
• Exocytosis

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Endocytosis

• A process by which a cell surrounds and takes in
  materials from its environment by engulfing them.

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Phagocytosis

• Process in which phagocytes engulf and digest
  microorganisms and cellular debris
• "phagocyte" or eating cell
• (phago "eating", cyte "cell").
• An important defense against infection

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Pinocytosis

• process by which certain cells can engulf and
  incorporate droplets of fluid

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Exocytosis

• when transport
• is out of the cell.

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