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.

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]