biological molecule 1

Question 1

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.

Answer 1

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. Examples of this include: amino acids AND polypeptides and
4. alpha glucose AND starch
5. a glycosidic bond is formed when the polymer is made.

Question 2

what forms a polymer that gives a positive result with a biuret test?

Answer 2

amino acids

Question 3

what is a monomer?

Answer 3

a chain of repeating units from which larger molecules/polymers are made

Question 4

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.

Answer 4

.heat with acid AND neutralise
. then heat with Benedict’s solution
. Red precipitate is formed

Question 5

A precipitate is produced in a positive result for reducing sugar in a
Benedict’s test.
A precipitate is solid matter suspended in solution.
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.

Answer 5

.Filter AND dry the precipitate
. find the mass

Question 6

Use of a colorimeter in an investigation would improve the repeatability of
the student’s results.
Give one reason why.

Answer 6

. Quantitative results
. Standardises the method

Question 7

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.

Answer 7

SIMILARITY = both contain galactose

DIFFERENCE = lactulose contains fructose, whereas lactose contains glucose

Question 8

Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage
molecule.

Answer 8

1. insoluble in water so does not affect water potential
2. coiled, so it makes molecule compact

Question 9

Describe the structure of glycogen.

Answer 9

. polysaccharide of alpha glucose
. joined by glycosidic bonds

Question 10

Suggest how glycogen acts as a source of energy

Answer 10

it can be hydrolysed into glucose that can be used in respiration

Question 11

Explain the difference in the structure of a starch molecule and a
cellulose molecule.

Answer 11

1. Starch formed from α-glucose but cellulose formed from β-glucose;
2. Position of hydrogen and hydroxyl groups on carbon atom 1
   inverted.

Question 12

Explain how cellulose molecules are adapted for their function in plant
cells.

Answer 12

. long, straight chains
. link together by hydrogen bonds to form fibrils,
. which provide strength to the cell wall

Question 13

Describe how you would test for the presence of a lipid in a liquid sample of
food.

Answer 13

. add ethanol to a sample and shake, then add an equal amount of water and shake. A milky white emulsion indicates a positive result

Question 14

Describe how a triglyceride molecule is formed

Answer 14

a condensation reaction occurs between 1 glycerol and 3 fatty acids, removing 3 molecules of water and forming ester bonds