1.3 Lipids ( biological molecules )

Question 1

name two groups of lipid

Answer 1

triglycerides and phospholipids

Question 2

describe the structure of a fatty acid

Answer 2

• variable R group - hydrocarbon chain
• -COOH = carboxyl group

Question 3

describe the difference between saturated and unsaturated fatty acids

Answer 3

• saturated = no C=C double bonds
• unsaturated = one more more C=C double bonds

Question 4

describe how triglycerides form

Answer 4

• 1 glycerol molecule and 3 fatty acids
• 3 condensation reactions
• removal of 3 water molecules
• forming 3 ester bonds

Question 5

explain how properties of triglycerides are related to their structure

Answer 5

• energy storage
  • high ratio of C-H bonds to carbon atoms
• so used in respiration to release more energy than the same mass of carbohydrates
  • hydrophobic / non polar fatty acids so insoluble in water
• so no effect on water potential of cell

Question 6

describe the difference between structure of triglycerides and phospholipids

Answer 6

• one of the fatty acids of triglyceride is substituted by a phosphate containing group

Question 7

describe how the properties of phospholipids relate to their structure

Answer 7

Function : form a bilayer in cell membrane , allowing diffusion of lipid soluble ( non polar ) or very small substances and restricting movement of water soluble ( polar) or larger substances
• phosphate heads are hydrophilic
- attracted to water so point to water either side of membrane
• fatty acid tails are hydrophobic
- repelled by water so point away from water

Question 8

describe the test for lipids

Answer 8

• add ethanol , shake then add water
• positive result of milky white emulsion