| Date | November 2013 | Marks available | 1 | Reference code | 13N.3.sl.TZ0.7 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | State | Question number | 7 | Adapted from | N/A |
Question
The following products result from the hydrolysis of a triglyceride.
\({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{31}}}}{\text{COOH}}\) \({{\text{C}}_{{\text{13}}}}{{\text{H}}_{{\text{27}}}}{\text{COOH}}\) \({{\text{C}}_{{\text{15}}}}{{\text{H}}_{{\text{29}}}}{\text{COOH}}\)
Draw a possible structure for the triglyceride.
State the other reactant and one essential condition that would favour this hydrolysis reaction in the body.
Identify which product is polyunsaturated, and outline why foods containing this type of fatty acid are important for health.
People who live in very cold regions need a diet with a higher ratio of fat to carbohydrate than people who live in warmer climates. Suggest why this is the case.
Markscheme
;
Accept alternative orders for the hydrocarbon tails.
water/\({{\text{H}}_{\text{2}}}{\text{O}}\) and enzyme/biological catalyst/lipase;
Accept acidic/alkaline/basic condition instead of water.
Do not award mark for lipase alone without water/ H2O.
\({{\text{C}}_{{\text{19}}}}{{\text{H}}_{{\text{31}}}}{\text{COOH}}\);
they lower level of LDL cholesterol/low-density lipoproteins / reduce (the risk of) heart disease;
Allow comparison with saturated fats with explanation.
fats provide more energy (per kg) than carbohydrates;
Do not allow “fat is an insulator”.
Examiners report
It was clearly a challenge for candidates to reconstruct the triglyceride and in (b) conditions for the formation (rather than hydrolysis) of the triglyceride were given. Careful reading of questions is important. If water was given in (b), the enzyme was omitted or replaced by “heat”. In (c), the unsaturated product was often given in place of the polyunsaturated and only cholesterol was discussed rather than LDL cholesterol. The common error in (d) was to state that lipids “provide better insulation”.
It was clearly a challenge for candidates to reconstruct the triglyceride and in (b) conditions for the formation (rather than hydrolysis) of the triglyceride were given. Careful reading of questions is important. If water was given in (b), the enzyme was omitted or replaced by “heat”. In (c), the unsaturated product was often given in place of the polyunsaturated and only cholesterol was discussed rather than LDL cholesterol. The common error in (d) was to state that lipids “provide better insulation”.
It was clearly a challenge for candidates to reconstruct the triglyceride and in (b) conditions for the formation (rather than hydrolysis) of the triglyceride were given. Careful reading of questions is important. If water was given in (b), the enzyme was omitted or replaced by “heat”. In (c), the unsaturated product was often given in place of the polyunsaturated and only cholesterol was discussed rather than LDL cholesterol. The common error in (d) was to state that lipids “provide better insulation”.
It was clearly a challenge for candidates to reconstruct the triglyceride and in (b) conditions for the formation (rather than hydrolysis) of the triglyceride were given. Careful reading of questions is important. If water was given in (b), the enzyme was omitted or replaced by “heat”. In (c), the unsaturated product was often given in place of the polyunsaturated and only cholesterol was discussed rather than LDL cholesterol. The common error in (d) was to state that lipids “provide better insulation”.
