Transport

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  • Created by: JasmineR
  • Created on: 06-12-15 15:20

Simple diffusion

  • Transport of substances through the phospholipid bilayer only.
  • Substances transported:
    • Lipid soluble molecules.
    • Very small molecules.
  • Transport is always down a concentration gradient (from a higher concentration to a lower concentration).
  • This process is passive (no ATP/energy is required).
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Facilitated diffusion

  • Transport of substances through specific transport proteins.
  • Transport of larger poar/water soluble molecules (e.g. glucose and amino acids) through transport proteins (can be called carrier proteins).
  • Transport of ions (e.g. sodium (Na+), potassium (K+) and chloride (Cl-)) through ion channels or pores.
  • Transport is always down a concentration gradient.
  • The process is passive (no ATP/energy required).
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Osmosis

  • Special type of simple diffusion.
  • Transport of water molecules only.
  • Water (although not lipid soluble) is small enough to pass through the phospholipid bilayer.
  • Transport is down a water potential gradient from higher (less negative) water potential to lower (more) negative water potential.
  • The process is passive (no ATP/energy required).
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Active transport

  • Transport of polar molecules and ions via transport proteins, same as facilitated diffusion.
  • However:
    • Transport is always against a concentration gradient (from a lower concentration to a higher concentration).
    • The process is active (it requres energy from ATP).
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