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Date November 2020 Marks available 1 Reference code 20N.3.sl.TZ0.7
Level SL Paper 3 Time zone TZ0
Command term Deduce Question number 7 Adapted from N/A

Question

The diverse functions of biological molecules depend on their structure and shape.

Classify vitamins A, C and D as either mainly fat- or water-soluble, using section 35 of the data booklet.

[1]
a.

The diverse functions of biological molecules depend on their structure and shape.

Deduce the straight chain structure of deoxyribose from its ring structure drawn in section 34 of the data booklet.

[1]
b(i).

The diverse functions of biological molecules depend on their structure and shape.

Sucrose is a disaccharide formed in the reaction of glucose with fructose.
Identify the reaction type and the newly formed functional group that joins the monosaccharide units in the product.

[2]
b(ii).

Markscheme

all three correct ✔

a.

CH2 must be placed next to CHO AND 2OHs on central carbons must be on same side (LHS or RHS) ✔

Accept crosses in place of C on three middle carbons.

b(i).

Reaction type:
condensation ✔

Accept “nucleophilic substitution/SN” for M1.

Functional group:
acetal/ether/glycosidic «linkage» ✔

Accept “glycoside” for M2.

b(ii).

Examiners report

Only a few very weak candidates answered this one wrongly.

a.

Very disappointing. I had only a few correct answers and the wrong ones very often showed no understanding at all. Some candidates drew ring structures even though a straight chain was requested.

b(i).

Many candidates scored both marks here. Ether was the most common answer for M2 with some responding glycosidic.

b(ii).

Syllabus sections

Options » B: Biochemistry » B.4 Carbohydrates
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Options » B: Biochemistry
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