lipids

• Role of lipids 

  • Source of energy = when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water
  • Waterproofing = lipids are insoluble in water both plants and insects have a waxy lipid cuticle that conserves water.
  • Insulation = fats are slow conductors of heat and when stored beneath the body surface, help to retain body heat. They also act as electrical insulators in myelin sheath around nerve cells
  • Protection = fat is often stored around delicate organs like the kidney.
• Triglycerides

  3 fatty acids each forming an ester bond with a glycerol via condensation reaction.
• There is a difference in properties of different fats and oils due to variations in fatty acids (over 70 fatty acids) and all have a carboxyl group and hydrocarbon chain attached.

  If the chain has no C-C double bond it is SATURATED.

  Single double bond = mono unsaturated

  More than one double bond = poly unsaturated.
• Triglycerides


  • High ratio of energy storing carbon-hydrogen bonds to carbon atoms
  • Good source of energy
• Lipids


  • Low mass to energy ratio
  • Good storage molecules because much energy can be stored in a small volume
  • Beneficial for animals as it reduces the mass they carry
• Lipids


  • Large and nonpolar
  • Insoluble in water so their storage doesn't affect osmosis in cells or water potential in them
• Triglycerides


  • High ratio of hydrogen to oxygen atoms
  • Release water when oxidised
  • Provide an important source of water especially for organisms in dry deserts
• Test for lipids:

  1. Take a completely dry and grease free test tube
  2. To 2cm3 of sample add 5cm3 of ethanol
  3. Shake thoroughly to dissolve any lipid in sample
  4. Add 5cm3 of water and shake gently
  5. Cloudy white emulsion = lipid is present
  6. As a control = repeat procedure with water instead of sample, final solution should be clear.
• better adapted to warm conditions because it

  more saturated fatty acids so more energy available (and more growth)
• 1. (is better adapted to cool conditions because it) has more unsaturated/liquid fatty acids so more lipase activity (and more growth);
• explain two ways in which fatty acids are important in the formation of new cells.

  • Fatty acids respired to release energy;More triglycerides more energy released;Energy used for cell production / production of named cell component;
  • Fatty acids used to make phospholipids; Phospholipids in membranes;More phospholipids more membranes made;
• This fat substitute is a lipid. Despite being a lipid, it cannot cross the cell-surface membranes of cells lining the gut. Suggest why it cannot cross cell-surface membranes.

  It is hydrophilic/is polar/is too large/is too big;