Biology exam questions - biological molecules

Question 1

Describe a biochemical test to show that raffinose solution contains a
non-reducing sugar

Answer 1

• heat with acid and neutralise
• heat with benedict’s solution
• red/ orange precipitate formed

Question 2

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 2

• filter and dry precipitate
• find the mass

Question 3

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 3

similarity - both contain galactose
difference - lactulose contains fructose whereas lactose contains glucose

Question 4

Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.

Answer 4

-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;
- glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has
only 1,4- glycosidic bonds;

Question 5

Describe and explain two features of starch that make it a good storage
molecule

Answer 5

Insoluble (in water), so doesn’t affect water potential;
coiled / (α-)helix so can fit many (molecules) in
small area;
4. Branched / more ends for fast breakdown / enzyme action

Question 6

Describe the structure of glycogen.

Answer 6

polysaccharide of alpha glucose
joined by glycosidic bonds
2 marks

Question 7

Explain one way in which starch molecules are adapted for their function in
plant cells

Answer 7

Insoluble;
Don’t affect water potential

2 marks

Question 8

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

Answer 8

Long and straight chains;
Become linked together by many hydrogen bonds to form
fibrils;
Provide strength (to cell wall).

Question 9

a) Describe how an ATP molecule is formed from its component molecules

Answer 9

• made from adenine, ribose and three phosphates
• condensation reaction
• catalysed by ATP synthase enzyme

Question 10

The new antibiotic is safe to use in humans because it does not inhibit the
ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase
is inhibited

Answer 10

Human ATP synthase has a different shape active site to
bacterial ATP synthase

Question 11

ATP is an energy source used in many cell processes. Give two ways in
which ATP is a suitable energy source for cells to use.

Answer 11

Releases energy instantaneously;
Phosphorylates other compounds, making them more reactive;
Can be rapidly re-synthesised;
Is not lost from / does not leave cells
( max 2) .

Question 12

Describe how ATP is resynthesised in cells.

Answer 12

• from ATP and inorganic phosphate
• from ATP synthase

Question 13

Give two ways in which the hydrolysis of ATP is used in cells.

Answer 13

• to release energy for respiration’
• to add inorganic phosphate to compounds to make them more reactive

Question 14

Describe the structure of DNA

Answer 14

Polymer of nucleotides;
Each nucleotide formed from deoxyribose, a phosphate (group) and
an organic/nitrogenous base;
Phosphodiester bonds (between nucleotides);
Double helix/2 strands held by hydrogen bonds;
(Hydrogen bonds/pairing) between adenine, thymine and
cytosine, guanine

Question 15

Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule

Answer 15

Condensation (reaction)/loss of water;
(Between) phosphate and deoxyribose;
(Catalysed by) DNA polymerase;

max two

Question 16

In the process of semi-conservative DNA replication, the two strands within
a DNA molecule are separated. Each then acts as a template for the
formation of a new complementary strand.
Describe how the separation of strands occurs.

Answer 16

DNA helicase;
Breaks hydrogen bonds between bases ( complementary base pairs)

Question 17

Describe the role of DNA polymerase in the semi-conservative replication
of DNA.

Answer 17

Joins (adjacent DNA) nucleotides;
(Catalyses) condensation (reactions);
(Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);

max two

Question 18

Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication

Answer 18

Watson and Crick

Question 19

Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments

Answer 19

Act as a template strand

Question 20

Use your knowledge of semi-conservative replication of DNA to suggest the role of DNA nucleotides

Answer 20

form complementary base pairs with bases on template strand

Question 21

Give two features of DNA and explain how each one is important in the
semi-conservative replication of DNA.

Answer 21

Weak / easily broken hydrogen bonds between bases allow two
strands to separate / unzip;
Two strands, so both can act as templates;
may appear in the same feature
Complementary base pairing allows accurate replication;