1.3 - Cell membranes and transport

• Cell membrane


  Partially permeable membrane composed of a sea phospholipids with protein molecules between the phospholipid molecules
• Cell membrane


  • Controlling the movement of substances in and out of the cell/organelle
  • Contains receptors for other molecules such as hormones
  • Enables adjacent cells to stick together
  • Fluid mosaic structure
• Factors affecting cell membrane permeability


  • Heat
  • Ethanol
  • pH
• Movement of molecules through cell membrane


  1. Diffusion

  2. Facilitated diffusion

  3. Osmosis

  4. Active transport

  5. Cytosis
• Diffusion


  Passive movement of small, non-polar lipid soluble molecules from an area of high concentration to an area of low concentration
• Facilitated diffusion


  Requires a channel protein in the cell membrane to transport polar molecules, charged and water soluble molecules across the membrane
• Osmosis


  Diffusion of water molecules from an area of low solute concentration to an area to high solute concentration through a partially permeable membrane
• Active transport


  Can transport all types of molecules through carrier proteins from an area of low concentration to an area of high concentration, requires energy in the form of ATP
• Cytosis


  Form of active transport where parts of the plasma membrane form infoldings or outfoldings, includes exocytosis and endocytosis
• As surface area increases


  The rate of gas exchange by diffusion becomes more rapid
• As diffusion distance decreases

  The rate of gas exchange by diffusion becomes more rapid
• As diffusion gradient becomes more steep

  The rate of gas exchange by diffusion becomes more rapid
• Water potential


  The pressure exerted by water molecules that are free to move in a system, measured in kPa
• As solutes are added to a solution

  The water potential of the solution falls
• Solute potential


  The contribution of solute to the water potential
• Cyanide


  A strong poison which inhibits respiration by inhibiting the enzyme cytochrome oxidase which catalyses the formation of ATP from ADP and inorganic phosphate, resulting in no ATP production and cell death