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Date	November 2018	Marks available	3	Reference code	18N.3.sl.TZ0.7
Level	SL	Paper	3	Time zone	TZ0
Command term	Determine	Question number	7	Adapted from	N/A

Question

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]

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]

b.i.

State two functions of lipids in the body.

[2]

b.ii.

Outline one effect of increased levels of low-density lipoproteins in the blood.

[1]

Markscheme

phosphoric acid ✔

glycerol/propane-1,2,3-triol ✔

Do not accept formulas.

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 «= $\frac{{1015.2\,{\text{g}}\,{\text{mo}}{{\text{l}}^{-1}}}}{{276.46\,{\text{g}}\,{\text{mo}}{{\text{l}}^{-1}}}} \times 100$ » = 367 ✔

ALTERNATIVE 2:

4 C=C bonds/4 carbon to carbon double bonds ✔

« $\frac{{100\,{\text{g}}}}{{276.46\,{\text{g}}\,{\text{mo}}{{\text{l}}^{-1}}}} \times 4$ =» 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.

b.i.

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”.

b.ii.

Any one of:

atherosclerosis/cholesterol deposition «in artery walls» ✔

heart/cardiovascular disease ✔

stroke ✔

Accept “arteries become blocked/walls become thicker”.