Diffusion%20

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Diffusion Osmosis
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Diffusion

• The movement of molecules from an area in which
  they are highly concentrated to an area in which
  they are less concentrated.

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Diffusion
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• Sugar molecules dissolve in water to make a
  homogeneous mixture.
• Sugar is the solute. H2O is the solvent. The
  mixture is a solution.

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Net movement of molecules stops when equilibrium
is reached
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MEMBRANE STRUCTURE AND FUNCTION

• Membranes organize the chemical activities of
  cells
• Membranes provide structural order for metabolism
  
• Forms most of the cell's organelles
• Compartmentalizes chemical reactions
• The plasma membrane forms a boundary between a
  living cell and its surroundings
• Exhibits selective permeability
• Controls traffic of molecules in and out

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Cell Membrane

• Controls movement of molecules into and out of
  the cell
• Selectively permeable
• Some substances can pass freely.
• Some substances can pass to an extent.
• Some not at all.
• Allow cells to maintain homeostasis.

Appears as a double layer under the electron
microscope
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Fluid-Mosaic Model of Cell Membrane

• Has two layers (a bilayer) of phospholipids (fats
  with phosphorous attached), in which protein
  molecules float, and which at body temperature
  are fluid. Why is it called a mosaic?

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The membrane is a fluid mosaic of phospholipids
and proteins

• A membrane is a mosaic because proteins and other
  molecules are embedded in a framework of
  phospholipids.
• A membrane is fluid. Most protein and
  phospholipid molecules can move laterally.
• Membrane glycoproteins and glycolipids function
  in cell identification.

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Passive transport is diffusion across a membrane

• Passive transport across membranes occurs when a
  molecule diffuses down a concentration gradient.
• Like moving down a hill, it requires no energy.
  

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Osmosis

• The diffusion of water across a selectively
  permeable membrane.
• Osmosis is a type of Passive Transport.
• Osmosis requires NO ENERGY.

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Osmosis
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Tonicity
Osmosis

• Hypotonic- a solution that causes a cell to swell
  because of Osmosis.
• Hypertonic- a solution that causes a cell to
  shrink because of Osmosis.
• Isotonic- a solution that causes no change in the
  size of the cell

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Hypotonic Solution

• In this picture a red blood cell is put in a
  glass of distilled water. Because theres 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. 

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Concentration of H20 depends on a amount of
dissolved solute

• So, answer this question.Why do establishments
  offer free popcorn, peanuts, and pretzels to
  their patrons if they are serving beverages?
  What changes are taking place in the body to
  initiate the need for more beverages?

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Selectively Permeable

• A membrane that allows only certain materials to
  cross it.
• Materials pass through pores in the membrane.
• What determines whether molecules can pass
  through a cell membrane?
• If a molecule is too large it cannot pass. The
  molecule has to be fairly small, O2, H2O, CO2 and
  a couple others can easily pass through the
  membrane. Also it depends on the concentration
  of a specific substance inside the cell.
  Similarly, if a molecule is polar it cannot
  penetrate the phospholipid bilayer.

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Summary

• Diffusion is the movement of molecules from an
  area of higher concentration to an area of lesser
  concentration.
• Osmosis is the movement of water thru a semi
  permeable membrane.
• Passive transport needs NO ENERGY! (molecules
  move from an area of higher to lesser
  concentration).
• Active transport requires energy. (molecules move
  from an area of lesser to higher concentration)

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Why are osmosis diffusion important?

• All living things have certain requirements they
  must satisfy in order to remain alive maintain
  homeostasis
• These include exchanging gases (usually CO2 and
  O2), taking in water, minerals, and food, and
  eliminating wastes.
• These tasks happen at the cellular level.
• Molecules move through the cell membrane by
  diffusion
• A balance, or EQUILIBRIUM, must be maintained.