lipids

• lipids contain higher proportion of H and low proportion of O
• function of lipids:

  • source of energy
  • store of energy
  • insulation - thermal and electrical
  • protection (leaf cuticle, internal organs)
  • buoyancy
• glycerol and fatty acids are key components of fats/oils for energy storage/supply and membranes
• fatty acids:

  • have COOH group
  • hydrocarbon chain
  • can be saturated or unsaturated
• polyunsaturated:


  more than one double bond
• monounsaturated


  only one double bond
• animals lipids often have saturated and occur as fats
• plant lipid are often unsaturated and occur as oils
• triglycerides hace 1 glycerol and 3 fatty acids

  • ester bond formed from an condensation reaction (esterification)
• phospholipid: similar to triglyceride except it replaces 1 of the fatty acids with a phosphate group
• phospholipids bilayer


  if placed in water phospholipid will arrange themselves in double layer with the hydrophilic phosphate heads pointing outwards and tails are hydrophobic

  double layer forms the phospholipid bilayer and basis of cell membrane
• micelle


  demonstrates amphipathic behaviour of phospholipids in water
• cholesterol a type of lipid

  • helps regulate fluidity and strength of the membrane
  • steroid hormones testosterone and oestrogen made from cholesterol
  • small size enables molecule to sit in hydrophobic part of the membrane and regulate fluidity
• energy source

  • triglycerides can be broken down in respiration to release energy and generate ATP
  • hydrolyse the ester bonds give you glycerol and fatty acids that can be broken down into CO2 and water
• energy store

  • insoluble in water, can be stored without it affecting water potential
  • high proportion of H atoms than carbohydrates and almost no O atoms
• insulation

  • mammals store fats in adipose cells under the skin- storage location for lipid in whales(blubber)acting as a heat insulator
  • lipid in nerve cells acts as an electrical insulator
  • animals preparing for hibernation stores extra fat
• buoyancy

  • because fat is less dense than water, it is used by aquatic animals to help them stay afloat
• protection

  • humans have fat around delicate organs, such as their kidneys to act as a shock absorber