Getting through the barrier of the cell membrane

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Getting through the barrier of the cell membrane

• Some substances pass through the membrane without
  any energy needed from the cell ? called passive
  transport
• Some substances need energy from the cell to pass
  through the membrane ? called Active Transport

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Passive Transport

• Passive Transport movement of molecules across a
  membrane WITHOUT any energy
• Three types 1. Diffusion
• 2. Facilitated Diffusion
• 3. Osmosis
• The Goal maintain homeostasis using the cell
  membrane as a barrier.

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Diffusion

• Diffusion movement of molecules of a substance
  from an area of HIGH concentration to an area of
  LOW concentration
• Ex sugar cube in water
• food coloring
• home cooking
• air freshener

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Diffusion

• There is a difference in concentration of the 2
  substances (food coloring water, water sugar,
  air freshener air)
• The difference in concentration across space/area
  ? concentration gradient
• When the concentration of a substance is the same
  all over ? Equilibrium!
• (molecules still moving at random)

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Diffusion

• Molecules tend to move DOWN the concentration
  gradient
• more (hi) concentration ? to less (low)
  concentration

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Diffusion Across Membranes

• Some molecules can diffuse across a membrane
  (with no aid/help) if they are soluble in lipids
• NOT all molecules can do this
• Also depends on 1. size type of molecule
• 2. structure of molecule

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Facilitated Diffusion

• The movement of molecules with the gradient (to
  an area of lower concentration) using a carrier
  protein for passage
• Carrier proteins are molecule specific, so only
  one type of molecule can move through them
• Occurs when regular diffusion cannot occur fast
  enough as needed (large molecules)
• Can go either into or out of cell depending on
  gradient

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OSMOSIS

• Osmosis
• Diffusion of water molecules through cell
  membrane
• Direction of osmosis is determined by the SOLUTE
  concentration

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DIRECTION OF OSMOSIS

• Depends on the concentrations of solutes water
• .
• THE WATER MOVES WHERE THERE IS MORE SOLUTE!

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Hypertonic Solution

• HIGH concentration of SOLUTE OUTSIDE the cell,
• LOW concentration of SOLUTE INSIDE the cell
• RESULT WATER MOVES OUT OF THE CELL.

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HYPOTONIC

• LOW concentration of SOLUTE OUTSIDE the cell
• HIGH concentration of SOLUTE INSIDE the cell,
• RESULT
• WATER MOVES INTO THE CELL.

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ISOTONIC

• inside and outside concentrations are equal.
• equal concentrations of solute water outside
  and inside the cell
• RESULT water diffuses in and out at constant
  rate, no net movement

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Osmosis in Cells
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OSMOSIS
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How does osmosis affect cells?

• Many cells live in isotonic solutions so
  equilibrium is easily attained
• But some do not
• Some unicellular freshwater organisms
• Plant cells

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Unicellular freshwater organisms

• Organisms live in hypotonic environments (lots of
  salt inside their cells) so they constantly take
  in water.
• If too much water enters ?cell dies, called
  cytolysis
• They have an organelle called a contractile
  vacuole that collects pumps out the excess
  water. This requires energy to be expended

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Contractile Vacuole of Amoebae
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Osmosis in Plants

• Plant cells also live in hypotonic solutions, so
  water enters the cell.. They like it ?
• Why?... Osmosis continues until vacuole is full
  the cell membrane is forced against the cell
  wall, called ? turgor pressure
• When a plant cell loses turgor pressure, the
  membrane collapses away from the cell wall,
  causing the plant to wilt, called ? plasmolysis

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Plasmolysis