Cell%20Membranes%20Osmosis%20and%20Diffusion

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Cell MembranesOsmosis and Diffusion
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Phospholipid Bilayer
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Functions of Membranes

• 1. Protect cell
• 2. Control incoming and outgoing substances
• 3. Maintain ion concentrations of various
  substances
• 4. Selectively permeable - allows some molecules
  in, others are kept out

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Cell Membranes are Semi-permeable

• Allows some substances into the cell, but screens
  out toxins and bacteria
• Substances allowed to cross include
• water, CO2, Glucose, O2, Amino Acids, Alcohol,
  and antihistamines. HIV and bacterial meningitis
  can cross the barrier.

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Methods of Transport Across Membranes

• 1. Diffusion -passive transport - no energy
  expended
• 2. Osmosis - Passive transport of water
  across membrane
• 3. Facilitated Diffusion - Use of proteins to
  carry polar molecules or ions across
• 4. Active Transport- requires energy to
  transport molecules against a concentration
  gradient energy is in the form of ATP

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Diffusion - the process by which molecules spread
from areas of high concentration, to areas of low
concentration. Osmosis the process by which
water molecules spread across a membrane from
areas of high concentration, to areas of low
concentration
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Blood
Blood
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Diffusion

• Movement of molecules from an area of high
  concentration to an area of low concentration.
• Movement from one side of a membrane to another,
  un-facilitated

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Diffusion
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Osmosis
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What determines the flow of materials in and out
of the cell?

• Hypotonic Solution - One solution has a lower
  concentration of solute than another.
• Hypertonic Solution - one solution has a higher
  concentration of solute than another.
• Isotonic Solution - both solutions have same
  concentrations of solute.

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Plant and Animal Cells put into various solutions
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Types of Transport
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These ABC proteins play a central role in all
living cells in the nutrient uptake, protein,
drug and antibiotic excretion, osmoregulation,
antigen presentation, signal transduction and
other important cellular functions.  
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