3.1.3 - Lipids

Question 1

roles of lipids

Answer 1

• in cell membranes
• source of energy
• waterproofing
• insulation
• protection

Question 2

triglyceride formation

Answer 2

• one glycerol
• three fatty acids (RCOOH)
• condensation reaction
• 3 water molecules removed
• 3 ester bonds formed

Question 3

saturated fatty acid

Answer 3

no double bonds between C atoms

Question 4

unsaturated fatty acid

Answer 4

one or more double bonds between C atoms (mono-unsaturated, polyunsaturated)

double bond(s) → molecule bends → cannot pack together closely → liquid (oils) at room temperature

Question 5

properties of triglycerides

Answer 5

• energy source: high ratio of energy-storing C-H bonds to C atoms
• storage: low mass to energy ratio, more energy in a small volume
• insoluble in water: do not affect osmosis/water potential of cells
• water source: high ratio of H to O atoms so release water when oxidised

Question 6

phospholipid structure

Answer 6

• triglyceride structure
• one fatty acid substituted by phosphate group
• hydrophilic ‘head’ attracted to water
• hydrophobic ‘tail’ repels water
• polar molecules

Question 7

properties of phospholipids

Answer 7

• bilayer formation: hydrophobic barrier formed between inside and outside of cell
• glycolipid formation: can combine with carbohydrates within cell membrane to form glycolipids used in cell recognition

Question 8

test for lipids

Answer 8

emulsion test:
- add ethanol
- shake/mix
- pour into/add water
- white/milky emulsion