MC test: Carbohydrates

Multiple choice test on B.4. Carbohydrates

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

Which statements must be true for a compound to be classed as a monosaccharide?

I. It must possess at least one hydroxyl group.

II. It must have the general formula (CH2O)n.

III. It must contain a carbonyl group.

Monosaccharides must contain at least two −OH groups. 2-hydroxyethanal (glycolaldehyde), , has a carbonyl group and has the general formula (CH2O)n but it is not a monosaccharide. Note that monosaccharides have the general formula (CH2O)n whereas polysaccharides have the general formula Cx(H2O)y.

 

Which is both an aldose and a pentose?

An aldose contains an aldehyde functional group −CHO and a pentose contains five carbon atoms

 

Which are furanoses?

I. ribose,

II. glucose

III. fructose

Furanoses contain five-membered rings. Glucose is a pyranose as it contains a six-membered ring.

 

What name is given to the bond formed when two monosaccharides condense together to form a disaccharide and water?

The glycosidic bond is the link via an oxygen atom (i.e. an ether) between a carbon atom from one monosaccharide with a carbon atom on another monosaccharide.  It is formed when two hydroxyl group condense with the loss of water,  −C−OH + HO−C−  → −C−O−C− + H2O

 

Which are polysaccharides?

I. starch

II. cellulose

III. glycogen

Starch and glycogen are energy storage polysaccharides whereas cellulose is a structural polysaccharide.

 

Carbohydrates provide a quick and convenient source of energy. The reaction can be summarized as complete combustion in oxygen to give carbon dioxide and water.
Which is the general equation for the combustion of any monosaccharide or polysaccharide?

Polysaccharides (e.g. sucrose C12H22O11) have the general formula Cx(H2O)y, only monosaccharides (where x = y) can be represented by (CH2O)n.

 

Which is the cyclic form of fructose, ?

The cyclic form of fructose will be a five-membered ring (furanose) with two -CH2OH groups (on the 1 and 4 carbon ring atoms).

 

Which two molecules are formed when one molecule of sucrose is hydrolysed in acid solution?

Sucrose:

Sucrose is formed from the condensation reaction between glucose and fructose. The acid hydrolysis of sucrose is the reverse of this reaction.

 

Why do humans need cellulose in their diet even though they do not possess enzymes in the digestive system that can break it down?

Cellulose acts as dietary fibre (roughage) which helps to prevent constipation and diverticulitis.

 

Which monomer can undergo polycondensation to form amylose?

Amylose:

Amylose (one of the forms of starch) is formed from the polycondensation of glucose molecules.

 

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