| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.sl.TZ1.7 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Identify | Question number | 7 | Adapted from | N/A |
Question
Saturated lipids found in butter and unsaturated lipids found in fish oil readily become rancid.
Identify the type of rancidity occurring in saturated lipids and the structural feature that causes it.
State one factor that increases the rate at which saturated lipids become rancid.
Butter contains varying proportions of oleic, myristic, palmitic and stearic acids. Explain in terms of their structures why stearic acid has a higher melting point than oleic acid, using section 34 of the data booklet.
Fish oil is an excellent dietary source of omega-3 fatty acids. Outline one impact on health of consuming omega-3 fatty acids.
Predict the solubility of retinol (vitamin A) in body fat, giving a reason. Use section 35 of the data booklet.
Explain why sharks and swordfish sometimes contain high concentrations of mercury and polychlorinated biphenyls (PCBs).
Plastics are another source of marine pollution. Outline one way in which plastics can be made more biodegradable.
Markscheme
hydrolytic «rancidity»
ester group
Accept a formula for ester group.
[2 marks]
«presence of» moisture/water
OR
«increase in» temperature
OR
«presence of» enzymes/bacteria/fungi/mould
OR
low pH/«presence of» acid
Accept “heat”.
[1 mark]
«stearic acid» straight chain/chain has no kinks/more regular structure
OR
«stearic acid» saturated/no «carbon–carbon» double bonds
«stearic acid» chains pack more closely together
stronger London/dispersion/instantaneous induced dipole-induced dipole forces «between molecules»
Accept “«stearic acid» greater surface area/electron density”.
[3 marks]
lowers risk of heart disease/atherosclerosis
OR
lowers LDL cholesterol
OR
increases HDL cholesterol
OR
aids brain/neurological development «in children»
OR
relieves rheumatoid arthritis
[1 mark]
soluble AND non-polar hydrocarbon chain
Accept as reasons “«predominantly» non-polar” OR “long hydrocarbon chain”.
[1 mark]
not biodegradable
OR
stored/accumulate in fat
biomagnification occurs
OR
concentration increases along food chain
Accept “stored/accumulate in bodies of prey/animals eaten”.
Accept “not excreted”.
[2 marks]
add starch/cellulose/carbohydrates/additives/catalysts «to plastic during manufacture to allow digestion by micro-organisms»
OR
replace traditional plastics with polylactic acid/PLA-based ones
OR
blend traditional and polylactic acid/PLA-based plastics
Accept reference to biodegradable plastics other than PLA; for example polyhydroxyalkanoates (PHA), poly(butylene succinate) (PBS), polybutylene adipate terephthalate (PBAT) and polycaprolactone (PCL).
[1 mark]
