3.1.2 Carbohydrates

Question 1

Monomer

Answer 1

Small units that can build up larger molecules

Question 2

Polymer

Answer 2

Long chain of repeating sub units called monomers, 3 or more monomers

Question 3

Dimer

Answer 3

2 monomers

Question 4

Condensation reaction

Answer 4

Forms a bond and removes a molecule of water

Question 5

Example of condensation reaction

Answer 5

Polypeptides from amino acids

(Allow a relevant example)

Question 6

Hydrolysis reaction

Answer 6

Bond broken through addition of water molecule

Question 7

Carbon containing compounds are ____________

Answer 7

Organic

Question 8

Saccharide

Answer 8

Sugar

Question 9

Isomers of glucose

Answer 9

Alpha and beta glucose

Question 10

Draw the structure of alpha glucose

Answer 10

See notes

Question 11

Draw the structure of beta glucose

Answer 11

See notes

Question 12

Difference between alpha and beta glucose

Answer 12

In beta glucose, the OH group is inverted

Question 13

Describe how to test for reducing sugars (3)

Answer 13

1. Add Benedict’s reagent
2. Heat in 95 degree water for 5 minutes
3. A positive result will show orange-brown

Question 14

Glucose + glucose =

Answer 14

Maltose

Question 15

Glucose and fructose =

Answer 15

Sucrose

Question 16

Glucose and galactose =

Answer 16

Lactose

Question 17

Explain how a disaccharide is formed (2)

Answer 17

1. Condensation reaction between two glucose monomers
2. Water molecule is removed and glycosidic bond forms

Question 18

Describe the test for non-reducing sugars (3)

Answer 18

(Disaccharide must be hydrolysed into monosaccharide)
1. Add dilute hydrochloric acid and place in boiling water for 5 minutes (hydrolyses the disaccharide)
2. Add in alkali (sodium hydrogen carbonate) to neutralise acid, so Benedict’s will work
3. Add Benedict’s reagent and add to 95 degree water and observe an orange/brown colour change

Question 19

Colorimeter - reducing sugar with lots of precipitate

Answer 19

Samples with high concentration of reducing sugar form lot’s of precipitate, so the colorimeter has a high absorbance and low transmission

Question 20

Describe the structure of starch (4)

Answer 20

Any four from
- Bonded by 1-6 glycosidic bonds
- Alpha glucose monomers
- Insoluble in water so doesn’t affect water potential or osmosis
- Large and insoluble so doesn’t diffuse out/in cell (good storage molecule)
- Unbranched and helical so lots can be stored (compact)
- When hydrolysed, forms alpha glucose monomers, used in respiration
- Branched ends can be acted on by enzymes

Question 21

State the two differences between starch and glycogen (2)

Answer 21

1. Glycogen found in animals
2. (Functions are the same however) glycogen is more highly branched, acted on faster by enzymes, important for organisms with high metabolic rate as rate of hydrolysis is faster

Question 22

Which isomer of glucose is cellulose formed from

Answer 22

Beta glucose

Question 23

Describe the structure of cellulose (3)

Answer 23

• Bonded by 1-4 glycosidic bonds
• Straight chains held together by weak hydrogen bonds forming microfibrils (strength and stability)
• Each adjacent glucose monomers rotates 180 degrees resulting in a straight chain

Question 24

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.

Give two named examples of polymers and their associated monomers to illustrate your answer (5)

Answer 24

1. A condensation reaction joins monomers together and forms a
   (chemical) bond and releases water;
2. A hydrolysis reaction breaks a (chemical) bond between
   monomers and uses water;
3. A suitable example of polymers and the monomers from which
   they are made;
4. and 4. Polymers must contain many monomers.
5. and 4: suitable examples include
   * amino acid and polypeptide, protein, enzyme,
   antibody or specific
   example
   * nucleotide and polynucleotide, DNA or RNA
   * Alpha glucose and starch/glycogen
   * Beta glucose and cellulose.

If neither specific carbohydrate example is given, allow
monosaccharide/glucose and polysaccharide.

3. and 4. Reject (once) reference to triglycerides.
4. A second suitable example of polymers and the monomers
   from which they are made;
5. Reference to a correct bond within a named polymer;

Reject reference to ester bond.