1.2 transport across cell membranes

• cell membrane


  controls entry/exit of substances

  
• phospholipids


  compound lipids of 2 fatty acids (1 unsaturated + 1 saturated), attached to a glycerol + phosphate head

  
• proteins


  large complex molecules, necessary for cells

  
• peripheral proteins


  attached temporarily, on the surface of the membrane,

  
• integral proteins


  permanently embedded in the cell membrane, moves molecules across them, on both sides of the membrane

  
• fluid mosaic model


  how cell membranes are made up of phospholipids and proteins

  
• permeable membrane


  substances can pass through
• selectively-permeable membrane


  some substances can pass through

  
• impermeable membrane


  nothing can pass through

  
• passive transport


  high to low concentration, no energy required (e.g, diffusion & osmosis)

  
• active transport


  low to high concentration, energy required (e.g, active transport)

  
• diffusion


  movement of molecules down the concentration gradient (e.g, perfume, teabag emersed, sugar dissolved)

  
• osmosis


  movement of water particles down the concentration gradient through a selectively-permeable membrane (e.g, plant roots absorbing water, raisins growing in water)

  
• plant cells are turgid


  hypotonic solution (distilled water)

  
• plant cells are normal


  isotonic solution (0.85% salt solution)
• plant cells are flaccid


  hypertonic solution (1.5% salt solution)

  
• plant cells are plasmolysed


  hypertonic solution (3% salt solution)

  
• animal cells burst


  hypotonic solution (distilled water)

  
• animal cells are normal


  isotonic solution (0.85% salt solution)

  
• animal cells shrink


  hypertonic solution (3% salt solution)