Facilitated Diffusion

  • Allows diffusion of large, membrane insoluble compounds such as sugars (glucose) and amino acids
  • Does not require energy (passive transport)
  • Substance binds to membrane transport protein
  • Molecules may enter the cell and leave the cell through the transport protein.
  • Particles move from areas of high concentration to areas of low concentration; diffuse

Active Transport

  • Movement across membrane with an energy cost because if moves the molecule against a concentration gradient
  • Used to pump specific compounds in or out of the cell
  • Requires energy to overcome the concentration gradient
  • Requires specific membrane transport proteins

Vesicle Transport (active transport)

Molecules too large to fit through the phosphoplipid bilayer or a protein carrier must enter a cell through vesicles instead.  This type of transport involves some rearrangement of the cell membrane.  Proteins and polysaccharides are examples of very large molecules that need to pass into and out of cells by way of vesicle transport.

Endocytosis – involves the pinching in of a portion of the cell membrane around the material to be transported into the cell.  The pinched-in portion eventually breaks off  from the cell membrane and forms a vesicle in the cytoplasm.

Phagocytosis (“cell eating”) – involves the movement of very large particles into the cell’s  interior

Pinocytosis (“cell drinking”) – involves the transport of liquids into vesicles

Receptor-mediated endocytosis (RME) – molecules bind to special receptor proteins located on the outside of the cell membrane.  Once enough molecules have gathered in an area, the cell membrane will transport these molecules into the cell.

Exocytosis – used to export very large molecules out of the cell; opposite of endocytosis

Vesicles are created within a cell at the Golgi complex; required for the secretion of  hormones, digestive enzymes, proteins, polysaccharides.

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