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Date May 2010 Marks available 1 Reference code 10M.2.SL.TZ1.2
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term State Question number 2 Adapted from N/A

Question

The equation below shows the production of glucose and galactose from lactose.

Glucose and galactose are examples of monosaccharides. State one other example of a monosaccharide.

[1]
a.

There are several different types of carbohydrate. State which type of carbohydrate lactose is.

[1]
b (i).

State the type of chemical reaction that occurs when lactose is digested into glucose and galactose.

[1]
b (ii).

Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of reaction is highest at 48°C. In food processing, lactase is used at a much lower temperature, often at 5°C. Suggest reasons for using lactase at relatively low temperatures.

[2]
d.

Markscheme

fructose/ribose/deoxyribose/ribulose/other monosaccharides apart from glucose and galactose

a.

disaccharide

b (i).

hydrolysis

b (ii).

less denaturation / enzymes last longer at lower temperatures;
lower energy costs / less energy to achieve 5° C compared to 48° C;
reduces bacterial growth / reduces (milk) spoilage;
to form products more slowly / to control rate of reaction;

d.

Examiners report

Candidates were often correct, but some stated a disaccharide instead of a monosaccharide. Common errors were sucrose or maltose.

a.

Most candidates correctly identified lactose as a disaccharide.

b (i).

Hydrolysis was often given, yet some erred by stating decomposition.

b (ii).

Generally answered well with most candidates referring to denaturation and/or controlling the rate of reaction.

d.

Syllabus sections

Core » Topic 2: Molecular biology » 2.3 Carbohydrates and lipids
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