methods of transport across cell membranes

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  • Created by: Leigh. x
  • Created on: 21-09-12 12:21

DIFFUSION

  • from hight to low concentration (untill equilibrium reached)

 

  • hydrophobic (lipid- soluble) or small uncharged molecules

eg. oxygen/ carbon dioxide

 

  • through phospholipid bilayer

 

  • passive, no energy required
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FACILITATED DIFFUSION

  • from hight to low concentration (untill equilibrium reached)

 

  • hydrophobic molecules or ions (large)

eg. Glucose

 

  • through channel protiens and carrier protiens (via protiens that change shape)
  • passive, no energy required
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OSMOSIS

  • a type of diffusion involving movement of free water molecules

 

  • from hight to low concentration (untill equilibrium reached)

 

  • through phospholipid bilayer

 

  • passive, no energy required
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Osmosis

(http://faculty.southwest.tn.edu/rburkett/GB1-os1.jpg)

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ACTIVE TRANSPORT

  • Agaisnt concentration gradient, low to high

eg. ions into root hairs, muscles and nerve cells

 

  • through carrier proteins that change shape
  • requires energy
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EXOCYTOSIS

  • with or against a concentration gradient

 

  • used for bulk transport of substances out of the cell, very large particles

eg. proteins, usually insulin, nuerotransmitters or polysaccharides

  • not through membranes
  • active energy is required
  • vesicles fuse with the cell surface membrane, releasing their contents
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ENDOCYTOSIS

  • with or without a concentration gradient
  • active, energy is required
  • used for bulk transport of substances into the cell, very large molecules or particles

eg. cholesterol, bacteria by white blood cells

  • vesicles are created from the cell surface membrane, bringing their contents into the cell
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