Movement across cell membranes

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  • Movement across Cell Membranes
    • Lipid Diffusion
      • Substance can move directy across the phospholipid bilayer, they must either be lipid soluble or be a very small molecule. Lipid diffusion is a passive process and can therefore only move down its concentration gradient.
    • Faciliated Diffusion
      • Still diffusion but the molecules are "helped" by intrinsic proteins. It allows non-lipid soluble substances to cross the membrane. However substances can only cross a membrane that contains their specif transport protein. Channel proteins allow charged substances to diffuse across membranes and Carrier proteins have a binding site for specific solute molecules.
    • Osmosis
      • The same as lipid diffusion but in water it is called osmosis. Osmosis is the movement of water molecules from where it is in high water potential to a low water potential through a selectively permeable membrane.
    • Active Transport
      • Active transport is the movement of substances across a membrane by an intrinsic protein pump. It can be done against the concentration gradient and it requires energy obtained from ATP produced during respiration. Cells that perform active transport will therefore contain more mitrochondria.
  • Still diffusion but the molecules are "helped" by intrinsic proteins. It allows non-lipid soluble substances to cross the membrane. However substances can only cross a membrane that contains their specif transport protein. Channel proteins allow charged substances to diffuse across membranes and Carrier proteins have a binding site for specific solute molecules.

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