Question 18N.3.sl.TZ0.7
| Date | November 2018 | Marks available | [Maximum mark: 8] | Reference code | 18N.3.sl.TZ0.7 |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce, Determine, Outline, State | Question number | 7 | Adapted from | N/A |
Lipids play several roles in our bodies.
A phospholipid generally consists of two hydrophobic fatty acids and a hydrophilic group.
Fatty acids are products of the acidic hydrolysis of phospholipids. Deduce the names of the other two products.
[2]
phosphoric acid ✔
glycerol/propane-1,2,3-triol ✔
Do not accept formulas.
The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.
Determine the iodine number of stearidonic acid, C17H27COOH.
[3]
ALTERNATIVE 1:
4 C=C bonds/4 carbon to carbon double bonds ✔
mass of iodine per mole of acid = «4 × 253.80 g mol–1 =» 1015.2 «g mol–1» ✔
iodine number «= » = 367 ✔
ALTERNATIVE 2:
4 C=C bonds/4 carbon to carbon double bonds ✔
« =» 1.447 mol of I2 «reacts with 100 g» ✔
iodine number «= 1.447 mol × 253.80 g mol–1» = 367 ✔
Award [3] for correct final answer.
State two functions of lipids in the body.
[2]
Any two of:
«structural» components of cell membranes ✔
energy storage/utilization ✔
«thermal/electrical» insulation ✔
transport «of lipid-soluble molecules» ✔
hormones/chemical messengers ✔
Accept other specific functions, such as “prostaglandin/cytokine/bile acid synthesis”, “cell differentiation/growth”, “myelination”, “storage of vitamins/biomolecules”, “signal transmission”, “protection/padding of organs”, “precursors/starting materials for the biosynthesis of other lipid”.
Outline one effect of increased levels of low-density lipoproteins in the blood.
[1]
Any one of:
atherosclerosis/cholesterol deposition «in artery walls» ✔
heart/cardiovascular disease ✔
stroke ✔
Accept “arteries become blocked/walls become thicker”.