1.3 - Lipids

Question 1

The general structure of a fatty acid is RCOOH. Name the group represented by COOH. (1)

Answer 1

• Carboxyl

Question 2

Describe how you would test for the presence of a lipid in a liquid sample of food. (2)

Answer 2

• Add ethanol/alcohol then add water and shake/mix
• White/milky (emulsion) or (emulsion) test turns white/milky

Question 3

Describe how a triglyceride molecule is formed. (3)

Answer 3

• One glycerol and three fatty acids;
• Condensation (reactions) and removal of three molecules of water
• Ester bond (formed)

Question 4

Describe how an ester bond is formed in a phospholipid molecule. (2)

Answer 4

• Condensation / Loss of water
• Between glycerol and fatty acid

Question 5

Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule. (1)

Answer 5

• Triglycerides are made of 3 fatty acids and one glycerol
• In phospholipid, one fatty acid is replaced by a phosphate group

Question 6

Describe how a saturated fatty acid is different from an unsaturated fatty acid. (1)

Answer 6

• Saturated single/no double bonds (between carbons)
• Unsaturated has (at least one) double bond (between carbons)

Question 7

Describe the charges of the phospholipid head and tail. (2)

Answer 7

• Phosphate heads are hydrophilic (attracts water)
• Phosphate tails are hydrophobic (repels water)