(PMT) Mark Scheme Answers Flashcards
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. (5m)
1) a condensation reaction joins monomers together and forms a chemical bond and release water
2) hydrolysis reaction breaks a chemical bond between monomers using water
3) A suitable example of polymers and the monomers from which they are made
4) second suitable example of polymers and the monomers from which they are made
5) Reference to a correct bond within a named polymer
What is a monomer ?
a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;
A biochemical test for reducing sugar produces a negative result with raffinose solution.
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar. (3)
- Heat with acid and neutralise;
- Heat with Benedict’s (solution);
- Red precipitate/colo
A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.
- Filter and dry (the precipitate)
- Find mass/weight
Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.
Similarity - both contain galactose / a glycosidic bond;
Differences - Lactulose contains fructose, whereas lactose contains glucose;
Gycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule.
- Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers);
- Cellulose molecule has straight chain and glycogen is branched;
- Cellulose has a straight chain and glycogen is coiled.
- Glycogen has both 1- 4 and 1-6 glycosidic bond whereas cellulose has only 1-4 glycosidic bond
Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage molecule
- Insoluble (in water), so doesn’t affect water potential;
- Branched / coiled / (α-)helix, so makes molecule compact;
(a) Describe the structure of glycogen.
- Polysaccharide of α-glucose; OR
- Joined by glycosidic bonds or branched structures.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer
- Hydrolysed (to glucose);
- Glucose used in respiration;
Name the monomers from which a maltose molecule is made.
2 x Glucose
(d) Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitrary units. (2)
Line of best fit drawn; Read off value at 0.45.
Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.
- Starch formed from alpha glucose but cellulose is formed from beta glucose
- Position of hydrogen and hydroxyl groups on carbon atom 1 inverted
Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in plant cells. ( 2 marks)
- Insoluble
- Doesn’t affect water potential
- Helical
- Compact
Explain how cellulose molecules are adapted for their function in plant cells. (3m)
- Long and straight chains
- Become linked together by many hydrogen
- Provide strength to cell wall.
The general structure of a fatty acid is RCOOH.
Name the group represented by COOH (1m)
Carboxyl
