1.2 Carbohydrates

Question 1

The monomers from which larger carbohydrates are made.

Answer 1

Monosaccharides

Question 2

3 common monosaccharides:

Answer 2

Glucose, galactose and fructose.

Question 3

A condensation reaction between two monosaccharides forms…

Answer 3

a glycosidic bond.

Question 4

Maltose is a disaccharide formed by condensation of…

Answer 4

two glucose molecules.

Question 5

Sucrose is a disaccharide formed by condensation of…

Answer 5

a glucose molecule and a fructose molecule.

Question 6

Lactose is a disaccharide formed by condensation of…

Answer 6

a glucose molecule and a galactose molecule.

Question 7

The condensation of α-glucose produces…

Answer 7

the polysaccharides glycogen and starch.

Question 8

The condensation of β-glucose produces…

Answer 8

the polysaccharide cellulose

Question 9

Describe how the structure of starch is related to its function.

Answer 9

1. Polysaccharide of α-glucose monomers. Glucose can be released to be used as a respiratory substrate (for example at night, when light dependent reaction of photosynthesis stops).
2. Glucose monomers joined with 1-4 and 1-6 glycosidic bonds, so branched / coiled / (α-)helix, so makes molecule compact, so can fit many (molecules) in small volume.
3. Mixture of amylose (helical and unbranched) and amylopectin (helical and branched). Amylose is more compact, amylopectin has more ends for hydrolytic enzyme action (to release glucose faster)
4. Large molecule, so can’t cross the cell membrane AND is insoluble (in water), so doesn’t affect water potential

Question 10

Describe how the structure of glycogen is related to its function.

Answer 10

1. Helix/coiled/branched so compact;
2. Polymer of glucose so easily hydrolysed;
3. Branched / (1-4 and) 1-6 glycosidic bonds, so more ends for faster hydrolysis;
4. Polymer of glucose (polymer) so provides respiratory substrate for energy release; [Nb glycogen releases glucose, not energy]
5. Insoluble so not (easily) lost (from cell)
   OR
   Insoluble so does not affect water potential/osmosis;

Question 11

Describe how the structure of cellulose is related to its function.

Answer 11

1. Polymer of β-glucose joined by 1-4 glycosidic bonds;
2. Alternate glucose monomers are upside down / rotated 180 degrees;
3. Results in a long AND straight, unbranched polysaccharide [this is cellulose]
4. Many cellulose molecules joined by hydrogen bonds to form microfibrils;
5. Provide strength and inelasticity (to cell wall).

Question 12

Which biochemical test indicates the presence of reducing sugars?

Answer 12

Benedict’s solution

Question 13

Which biochemical test indicates the presence of starch?

Answer 13

Iodine/potassium iodide