3.1.3 - LIPIDS

Question 1

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

Answer 1

carboxyl group

Question 2

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

Answer 2

1. add ethanol/alcohol then add water and shake/mix
2. white/milky emulsion

Question 3

describe how a triglyceride molecule is formed (3)

Answer 3

1. one glycerol and three fatty acids
2. condensation reactions and removal of three molecules of water
3. ester bonds formed

Question 4

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

Answer 4

1. condensation reaction
2. between glycerol and fatty acid

Question 5

describe how you would test a piece of food for the presence of lipid (2)

Answer 5

1. dissolve the sample in alcohol, then add water
2. white/milky emulsion

Question 6

name the type of bond between a glycerol and fatty acid (1)

Answer 6

ester bond

Question 7

a triglyceride is formed by condensation. from how many molecules is this triglyceride formed from? (1)

Answer 7

4

Question 8

the structure of a phospholipid molecule is different from that of a triglyceride. describe how a phospholipid is different. (2)

Answer 8

1. addition of a phosphate group
2. instead of one of the fatty acids

Question 9

omega-3 fatty acids are unsaturated. what is an unsaturated fatty acid? (2)

Answer 9

when double bonds are present between carbon atoms

Question 10

compare and contrast the structure and properties of triglycerides and phospholipids (5)

Answer 10

1. both contain ester bonds
2. both contain glycerol;
3. fatty acids on both may be saturated or unsaturated
4. both are insoluble in water;
5. both contain C, H and O but phospholipids also contain P;
6. triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
7. triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
8. Phospholipids form micelle/bilayer (in water) but triglycerides don’t

Question 11

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

Answer 11

in phospholipid, one fatty acid replaced by a phosphate

Question 12

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

Answer 12

saturated has no double bonds between carbons

OR

unsaturated has at least one double bond between carbons

Question 13

explain why phospholipids can form a bilayer but triglycerides cannot (3)

Answer 13

1. phospholipid both hydrophobic and hydrophilic
2. triglycerides only hydrophobic
3. hydrophilic region attracts water