| Date | May 2012 | Marks available | 2 | Reference code | 12M.3.sl.TZ2.B3 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Identify and State | Question number | B3 | Adapted from | N/A |
Question
Low-density lipoproteins (LDL) can cause cholesterol to line the walls of the arteries and lead to cardiovascular disease. High-density lipoproteins (HDL) are smaller than low-density lipoproteins.
The formulas of linoleic acid and linolenic acid are given in Table 22 of the Data Booklet. Many vegetable oils are advertised as being a good source of omega-6 fatty acids whereas green leaves are a good source of omega-3 fatty acids.
(i) Identify the major source of low-density lipoproteins.
(ii) State the importance of high-density lipoproteins.
Compare the chemical structures of linoleic acid, an omega-6 fatty acid, and linolenic acid, an omega-3 fatty acid.
Markscheme
(i) saturated fats / fats derived from lauric/myristic/palmitic acid / the liver;
(ii) remove cholesterol from the arteries / transport cholesterol to the liver / protect against heart attack/disease;
both unsaturated fatty acids;
linoleic acid has one less C=C bond/carbon to carbon double bond/is less unsaturated / linolenic acid has one more C=C bond/carbon to carbon double bond/is more unsaturated;
in linoleic the first C=C bond occurs further from the end of hydrocarbon chain / in linolenic the first C=C bond occurs closer from the end of hydrocarbon chain;
both contain 18 carbon atoms;
Examiners report
Most candidates answered part (a) correctly. One respondent stated in the G2 form that ªstudents are not required to know a major source of LDL”, which is a fair comment and will be addressed in future paper editing.
Part (b)(i) proved more challenging and many candidates lost marks resulting from the use of vague terms as “double bonds” rather than “carbon to carbon double bond”. Weaker candidates merely copied the structures from the Data Booklet and even strong candidates often failed to correctly refer the position of the carbon to carbon double bonds.
