exam questions lipids

• The structure of a

  phospholipid molecule is different from that of a triglyceride. Describe how.

  [2]

  triglyceride has three fatty acids and phospholipid has two;

  no phosphate group present in triglyceride but present in phospholipid.
• What is an unsaturated fatty acid?

  double bonds) between carbon atoms
• The general structure of a fatty acid is RCOOH. Name the group represented by COOH

  • Carboxyl;
• Describe how you would test for the presence of a lipid in a liquid sample of food.

  • Add ethanol/alcohol then add water and shake/mix
  • White/milky (emulsion)
• Describe how a triglyceride molecule is formed

  1. One glycerol and three fatty acids

  2. Condensation (reactions) and removal of three molecules of water

  3. Ester bond(s) (formed);
• Describe how an ester bond is formed in a phospholipid molecule

  1. Condensation (reaction)
  2. Between of glycerol and fatty acid;
• Describe how you would test a piece of food for the presence of lipid.

  1. Dissolve in alcohol, then add water;
  2. White emulsion shows presence of lipid
• How does the structure of phospholipids relate to their function in membranes? (3)

  Answer: The hydrophilic phosphate head faces water, while the hydrophobic fatty acid tails face inward, forming a bilayer that controls entry/exit of molecules
• Compare saturated and unsaturated fatty acids. (2)

  Answer: Saturated fatty acids have no double bonds, making them solid at room temperature. Unsaturated fatty acids have at least one double bond, making them liquid.
• How do triglycerides function as energy storage molecules? (2)

  Answer: They have a high energy-to-mass ratio, providing more energy per gram than carbohydrates and are insoluble, so they do not affect water potential.