3.1.3 Lipids

Question 1

what are the four functions of lipids?

Answer 1

• provide a source of energy
• help to insulate organisms
• act as waterproofing
• form membranes and hormones

Question 2

what are the two groups of lipid?

Answer 2

triglycerides and phospholipids

Question 3

how are triglycerides formed?

Answer 3

by the condensation reaction of one molecule of glycerol and three molecules of fatty acid

Question 4

how are phospholipids formed?

Answer 4

by the condensation reaction of one molecule of glycerol, two molecules of fatty acid and one phosphate-containing group

Question 5

the condensation reaction between glycerol and a fatty acid forms a ___ bond?

Answer 5

ester

Question 6

what is a saturated fatty acid?

Answer 6

it contains single carbon bonds only

Question 7

what is an unsaturated fatty acid?

Answer 7

it contains at least one double carbon bond

Question 8

why do unsaturated fatty acids have a lower melting point than saturated fatty acids?

Answer 8

• double carbon bonds create a kink in the hydrocarbon tail
• this weakens intermolecular forces
• intermolecular forces require less energy to overcome

Question 9

how does the structure of triglycerides relate to their properties?

Answer 9

the fatty acids chains are hydrophobic which makes lipids insoluble in water

Question 10

how does the structure of phospholipids relate to their properties?

Answer 10

• phosphate group is hydrophilic
• fatty acid chains are hydrophobic
• this allows phospholipids to form a bilayer

Question 11

why is the phosphate group in a phospholipid hydrophilic?

Answer 11

it is ionic which allows it to interact with water

Question 12

what is the food test for a lipid?

Answer 12

• add ethanol then water and shake
• milky emulsion formed