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Date November 2017 Marks available 2 Reference code 17N.3.sl.TZ0.9
Level SL Paper 3 Time zone TZ0
Command term Describe Question number 9 Adapted from N/A

Question

Lactose is a disaccharide formed by the condensation reaction of the monosaccharides galactose and glucose.

Describe what is meant by a condensation reaction.

[2]
a.

Draw the structure of galactose on the skeleton provided.

[1]
b.

Explain how the inclusion of carbohydrates in plastics makes them biodegradable.

[2]
c.

Markscheme

«reaction in which» two reactants/molecules/functional groups bond/react «to form a larger molecule/single main product»

small/tiny molecule

OR

H2O formed

Accept formula or name of a specified small molecule other than water such as ammonia, ethanoic/acetic acid,
ethanol, hydrogen sulfide etc. for M2.

Do not accept just “molecule formed”.

Award [1 max] for an example giving an equation of a condensation reaction such as the formation of a disaccharide.

a.

Accept “alpha” or “beta” form of galactose.

b.

Any two of:

makes the plastic more hydrophilic/water soluble

carbohydrates are broken down/hydrolysed by bacteria/microorganisms

makes plastic more accessible to bacteria as holes/channels are created

OR

plastic of lower density is more permeable/susceptible to water/oxygen/heat/pressure

weakens intermolecular/London/dispersion/instantaneous induced dipole-induced dipole forces «between polymer chains in the plastic»

Accept “van der Waals/vdW” for “London” forces.

[Max 2 Marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Options » B: Biochemistry » B.1 Introduction to biochemistry
Options » B: Biochemistry
Options

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