Movement of Materials Through The Cell Membrane

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Movement of Materials Through The Cell Membrane

• For a cell to maintain its internal environment,
• (i.e., achieve homeostasis) it has to be
  selective in the materials it allows to cross its
  cell membrane.
• Transport How molecules and fluids pass through
  the cell membrane.

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Movement of Materials Through The Cell Membrane

• Movement of molecules across the cell membrane
  depends on
• (A) concentration difference
• (B) membrane permeability
• (C) size and type of particle
• (D) temperature and pressure

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Movement of Materials Through The Cell Membrane

• Three types of passive transport (i.e., no energy
  is required).
• 1. Diffusion The process by which molecules of
  a substance move from an area of higher
  concentration of that substance to areas of
  lower concentrations.

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Movement of Materials Through The Cell Membrane
Diffusion
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Movement of Materials Through The Cell Membrane

• 2. Facilitated diffusion The use of carrier
  proteins to move lipid insoluble substances
  through the cell membrane.
• Like diffusion and osmosis, no energy is used,
  but a concentration difference must exist for
  movement to occur. Example, transport of glucose.

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Movement of Materials Through The Cell Membrane
Facilitated Diffusion
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Movement of Materials Through The Cell Membrane

• 3. Osmosis The diffusion of water molecules
• through a selectively permeable membrane from an
  area of higher concentration of water to an area
  of lower concentration of water.
• It continues until equilibrium is reached.
• Aquaporins are water channel proteins that allow
  water to pass through cell membranes.

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Movement of Materials Through The Cell Membrane
Osmosis
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Osmosis

• Osmotic pressure is the force caused by the net
  movement of water by osmosis.
• Two adjacent solutions are isotonic if they have
  the same concentrations of solute.
• Hypertonic solutions have a higher concentration
  of solute compared to another solution.
• Hypotonic solutions have a lower concentration of
  solute compared to another solution.

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