Diffusion and Osmosis

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Diffusion and Osmosis

• GETTING IN OUT OF CELLS

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Passive Transport

• Cell membranes help organisms maintain
  homeostasis by controlling what substances may
  enter or leave cells. Some substances can cross
  the cell membrane without any input of energy by
  the cell. The movement of such substances across
  the membrane is known as passive transport.

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Passive Transport

• Examples
• Diffusion
• Osmosis
• Facilitated diffusion

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Methods of Transport

• Diffusion the random movement of particles of a
  solute from an area of higher concentration to an
  area of lower concentration.
• Particles always move with (down) a concentration
  gradient (the difference in concentrations across
  a membrane).
• Passive transport.

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Molecules move from higher to lower concentration
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Diffusion

• Diffusion stops at equilibrium (when the
  concentrations across a membrane are equal).
• The movement of molecules continues at
  equilibrium but the of molecules moving across
  the membrane remains the same.

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Osmosis

• the diffusion of water through a selectively
  permeable membrane.
• Passive transport
• Water molecules move from a higher concentration
  OF WATER to a lower concentration OF WATER.
• Water will move to where there is a greater
  amount of solute because there is less water
  there.

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Isotonic solutions the concentration of solute
inside and outside of the cell is the same.

• Osmosis does not occur because equilibrium has
  already been reached.

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Hypotonic solutions the concentration of solute
is lower outside the cell than inside the cell.

• Have more water outside the cell so water moves
  into the cell
• Causes an increase in pressure inside the cell
  called turgor pressure (plants) or osmotic
  pressure (animals).
• Increase in pressure in animal cells causes them
  to swell or even burst gives plant cells shape
  and support.

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Hypertonic solutions the concentration of solute
is higher outside the cell than inside the cell.

• Have more water inside the cell so water moves
  out of the cell
• Causes a drop in turgor or osmotic pressure
  called plasmolysis.
• Plasmolysis causes animal cells to shrivel up and
  plants to wilt.

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The effect of osmosis in a) hypertonic solution
b) isotonic solution c) hypotonic solution.