1 Biological molecules
Exam-style questions
AQA Biology
1
The statements in the table below refer to three polysaccharide molecules.
Complete the table. If the statement is correct, place a tick () in the box and if
the statement is incorrect place a cross () in the box.
Statement
Starch
Cellulose
Glycogen
glycosidic bonds present
polymer of α-glucose
unbranched chains only
only found in plants
(4 marks)
2
Figure 1 shows the structure of a molecule of lactose.
Figure 1
a
Draw a diagram to show the monosaccharides formed when lactose is
hydrolysed.
(2 marks)
b Name the enzyme which catalyses the hydrolysis of lactose.
(1 mark)
c
Lactose is a reducing sugar. Describe how you would test a liquid to show it
contained reducing sugar.
(3 marks)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
1
1 Biological molecules
Exam-style questions
AQA Biology
3
Amylase is an enzyme. It catalyses the breakdown of starch to maltose.
Students mixed a starch solution with amylase. The concentration of amylase
and the concentration of starch were controlled.
They recorded the concentration of maltose at intervals for 30 minutes.
Figure 2 shows their results.
Figure 2
a
Suggest two other factors the students would have controlled.
(2 marks)
b Describe how the concentration of maltose changed over the period shown in
Figure 2.
(2 marks)
c
i
A tangent has been drawn to the curve in Figure 2. Explain how you
could use this line to calculate the initial rate of reaction.
(1 mark)
ii
The rate of reaction was lower after 10 minutes than it was at the start.
Explain why.
(2 marks)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
2
1 Biological molecules
Exam-style questions
AQA Biology
4
a
Describe how you could carry out the emulsion test to show that olives
contain lipids.
(3 marks)
Figure 3 shows the structure of a phospholipid molecule.
Figure 3
b i
Name the parts of the molecule labelled X and Y.
X ………………………………………
Y …………………………………….…
ii
(2 marks)
Z is a fatty acid. Fatty acids can be saturated or unsaturated. Describe the
difference between a saturated fatty acid and an unsaturated fatty acid.
(2 marks)
c
Describe how a phospholipid molecule differs in structure from a triglyceride
molecule.
(1 mark)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
3
1 Biological molecules
Exam-style questions
AQA Biology
5
Figure 4 shows a molecule of a protein called lactalbumin.
Figure 4
a
Give the name of the chemical group found at A.
(1 mark)
b Lactalbumin has a tertiary structure. Using evidence from the diagram,
describe the tertiary structure of a protein.
(2 marks)
c
Lactalbumin does not have a quaternary structure. Use the diagram to
explain why.
(1 mark)
d Lactalbumin is not a conjugated protein. Use the diagram to explain why.
(1 mark)
6
A student carried out an investigation using salivary amylase. Six wells (holes) of
the same size were cut in a starch agar plate. Each well was filled with the same
concentration and volume of amylase solution. An equal volume of buffer
solution was added to produce a different pH in each well. The plates were
incubated at 25 °C for 24 hours and then covered with iodine solution. The iodine
turned the starch blue-black. It was observed that there were clear rings around
some wells. The width of these clear rings is shown in the table.
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
4
1 Biological molecules
Exam-style questions
AQA Biology
a
pH
Width of clear ring / mm
1
0
3
2
5
6
7
11
9
5
11
0
There are clear rings around some of the wells. Explain why.
(2 marks)
b Calculate the rate of reaction at pH 7. Show your working.
(2 marks)
c
The student concluded that the optimum pH for amylase activity was pH 7.
This conclusion may not be valid. Explain why.
(1 mark)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
5
1 Biological molecules
Exam-style questions
AQA Biology
d Use your knowledge of enzyme structure to explain the result obtained at pH 11.
(3 marks)
e
Describe a control experiment for this investigation.
(2 marks)
© Oxford University Press 2015
www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
6