AQA GCSE Biology Biology Paper 1 (Higher), November 2021: Question 5
17 marks · Standard Demand difficulty · Extended Answer
Explain enzyme action using the lock and key model, identify production sites of amylase, and analyze an experiment investigating the effect of temperature on amylase activity.
Practise this questionQuestion
Question text
05 Amylase is an enzyme that breaks down starch.
05.1 Amylase is a polymer of smaller molecules.
Name the type of smaller molecule.
[1 mark]
05.2 Name the three parts of the human digestive system that produce amylase.
[2 marks]
05.3 Explain how amylase breaks down starch.
Answer in terms of the ‘lock and key theory’.
[3 marks]
A student investigated the effect of temperature on the activity of amylase.
Figure 8 shows the apparatus used.
Figure 8
This is the method used.
1. Set up the apparatus as shown in Figure 8.
2. After 5 minutes, pour the starch solution into the amylase solution and mix.
3. Remove one drop of the starch-amylase mixture and place onto a spotting tile.
4. Immediately add two drops of iodine solution to the starch-amylase mixture on the
spotting tile.
5. Record the colour of the iodine solution added to the starch-amylase mixture.
6. Repeat steps 3 to 5 every minute until the iodine solution stays yellow-brown.
7. Repeat steps 1 to 6 using water at different temperatures.
05.4 Name two control variables the student used in the investigation.
[2 marks]
05.5 Why did the student leave the starch solution and amylase solution for 5 minutes
before mixing them?
[1 mark]
Table 3 shows the results of the investigation.
Table 3
Time taken until iodine solution
Temperature in °C
stays yellow-brown in minutes
5 did not become yellow-brown
20 5
35 2
50 7
65 14
80 did not become yellow-brown
05.6 What conclusion can be made about the effect of temperature on amylase activity
between 20 °C and 65 °C?
[1 mark]
05.7 Explain the results at 5 °C and at 80 °C.
Use Table 3.
[5 marks]
05.8 The student investigated the effect of temperature on amylase activity.
Describe how the student could extend the investigation to determine the effect of a
different factor on amylase activity.
[2 marks]
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
05.1 amino acid(s) ignore monomers 1 AO1
4.2.2.1
05.2 in any order 2 AO1
salivary gland ignore mouth 4.2.2.1
pancreas
small intestine allow duodenum / ileum
do not accept large intestine
ignore intestine unqualified
all three correct for 2 marks
two correct for 1 mark
05.3 starch / substrate binds to active ignore starch / substrate fits 1 AO1
site (of enzyme) active site (of enzyme) 4.2.2.1
(because) shape of active site allow shape of starch / substrate 1
and substrate are and active site allow them to fit
complementary together
a chemical reaction occurs to allow maltose / sugars for 1
produce smaller molecules smaller molecules
or
bonds between the (starch)
molecules are broken to
produce smaller molecules
05.4 any two from: 2 AO2
• time before mixing (starch ignore time unqualified 4.2.2.1
and amylase) solutions RPA5
• volume / 5 cm3 of starch
(solution)
• volume / 1 cm3 of amylase
(solution) allow amount as an
• volume / 1 drop of mixture alternative to volume once
only
added to spotting tile
• volume / 2 drops of iodine
(solution)
do not accept temperature
05.5 to allow the solutions to reach allow so the solutions can 1 AO2
the same temperature as the equilibrate with the temperature 4.2.2.1
water of the water RPA5
or
to allow both solutions to reach
5 °C
05.6 as temperature increases, ignore reference to time 1 AO3
(amylase / enzyme) activity 4.2.2.1
increases, to 35 °C after which RPA5
activity decreases
05.7 allow enzyme for amylase and AO2
substrate for starch throughout 4.2.2.1
(iodine is not yellow-brown 1 RPA5
because) starch is still present
or starch has not been broken
down
at 5 °C amylase / starch / 1
molecules have low (kinetic)
energy
(therefore) there are fewer allow fewer enzyme-substrate 1
(enzyme-substrate) collisions complexes are formed
at 80 °C the amylase has been do not accept the amylase is 1
denatured killed / has died
allow the shape of the amylase /
active site changes
(so) the starch can no longer fit allow the bonds holding the 1
amylase in its (3D) shape have
broken
05.8 keep temperature constant 1 AO3
4.2.2.1
(but) change named factor and named factor e.g. pH or enzyme 1 RPA5
test a range of values of named concentration or substrate
factor concentration or inhibitor
concentration
Total 17
How to answer it
Enzymes, Digestion & Temperature (RPA 5)
This question assesses fundamental knowledge from Topic 2: Organisation and experimental skills from Required Practical 5 (Investigating Enzymatic Reactions):
- Chemical structure of enzymes: Identifying enzymes as proteins made of amino acids.
- Sites of production: Stating the three organs where amylase is produced in the human digestive system.
- Lock and Key mechanism: Explaining complementary fit, active sites, and product formation.
- Experimental design: Identifying controlled variables, equilibrating solutions, and extending investigations.
- Data analysis & biological explanation: Interpreting optimum temperatures, kinetic energy at low temperatures, and denaturation at high temperatures.
Structure of Enzymes
Amylase is a polymer of smaller molecules. Name the type of smaller molecule.
✅ Correct Answer
Amino acid(s)
💡 Key Knowledge
Enzymes are proteins. All proteins are biological polymers formed by folding long chains of amino acids.
❌ Common Errors
Do not write monomers (the question asks for the specific biological type of molecule). Do not confuse proteins with starch (which is made from glucose).
Sites of Amylase Production
Name the three parts of the human digestive system that produce amylase.
✅ Correct Answer
- Salivary glands
- Pancreas
- Small intestine (allow duodenum or ileum)
❌ Common Errors & Misconceptions
- Writing mouth instead of salivary glands (mouth is ignored by the mark scheme).
- Writing stomach (the stomach produces pepsin/protease, not amylase; amylase would be denatured by stomach acid).
- Writing large intestine (not accepted) or unqualified intestine .
The Lock and Key Theory
Explain how amylase breaks down starch. Answer in terms of the 'lock and key theory'.
✅ Correct 3-Step Answer
- Starch (the substrate) binds to the active site of amylase (the enzyme).
- The shape of the active site and the substrate are complementary.
- A chemical reaction occurs to produce smaller molecules (or bonds in starch are broken down into maltose / simple sugars).
🧠 Exam Technique
- Complementary vs Same: Never say the active site and substrate have the "same" shape! They fit together like a lock and key, meaning their shapes are complementary.
- Always name the specific parts: active site and substrate / starch.
- State the outcome: bonds break to form smaller molecules / maltose.
Control Variables in RPA 5
Name two control variables the student used in the investigation.
✅ Any TWO from the following (1 mark each):
- Time before mixing starch and amylase solutions (e.g. 5 minutes)
- Volume of starch solution (e.g. 5 cm³)
- Volume of amylase solution (e.g. 1 cm³)
- Volume / number of drops of mixture added to the spotting tile (e.g. 1 drop)
- Volume / number of drops of iodine solution (e.g. 2 drops)
🧠 Exam Technique
Always state volume rather than just "amount" or "size". The word "amount" is only accepted once. Do not write "temperature" – temperature is the independent variable being changed!
Equilibration of Temperature
Why did the student leave the starch solution and amylase solution for 5 minutes before mixing them?
✅ Correct Answer
To allow the solutions to reach the same temperature as the water bath (or to allow both solutions to reach the target temperature / 5 °C).
💡 Key Knowledge
Liquids take time to warm up or cool down. If mixed immediately, the reaction would start at room temperature, not the test temperature, making the test unfair and inaccurate.
Describing Trends from Data
What conclusion can be made about the effect of temperature on amylase activity between 20 °C and 65 °C?
✅ Correct Answer
As temperature increases, enzyme (amylase) activity increases up to 35 °C, and above 35 °C activity decreases.
🧠 Reading the Table Correctly
At 35 °C, the time taken is 2 minutes (the shortest time). Shortest time = fastest rate / highest activity (the optimum temperature).
❌ Common Trap
Do not simply state "time decreases then increases". The question asks for the effect on enzyme activity, so your answer must explicitly refer to activity or rate of reaction.
Explaining Results at Temperature Extremes
Explain the results at 5 °C and at 80 °C. Use Table 3.
✅ Mark-by-Mark Breakdown (5 Marks)
- Observation link [1 mark]: Iodine did not turn yellow-brown because starch is still present (starch has not been broken down).
- Low temp mechanism - Energy [1 mark]: At 5 °C, amylase and starch molecules have low kinetic energy.
- Low temp mechanism - Collisions [1 mark]: Therefore, there are fewer collisions between enzyme and substrate (or fewer enzyme-substrate complexes formed).
- High temp mechanism - Denaturation [1 mark]: At 80 °C, the amylase has been denatured (the active site has changed shape).
- High temp mechanism - Consequence [1 mark]: Starch can no longer fit / bind into the active site.
❌ Major Exam Misconception
NEVER say an enzyme is "killed" or "dies"! Enzymes are non-living chemical molecules. Always say the enzyme is denatured.
🧠 Why Students Lost Marks
Many students forgot to mention what the result ("did not become yellow-brown") actually means: starch was not broken down. Always state the biological meaning of the observation before explaining the mechanism!
Extending the Investigation
Describe how the student could extend the investigation to determine the effect of a different factor on amylase activity.
✅ 2-Mark Method
- Mark 1: Keep temperature constant (controlled).
- Mark 2: Change a named factor (e.g. pH, enzyme concentration, or substrate concentration) and test a range of values (e.g. pH 4, 5, 6, 7, 8).
🧠 Exam Strategy
When asked to investigate a "different factor":
- Turn the previous independent variable (temperature) into a control variable.
- Name a clear biological factor (most commonly pH using buffer solutions).
- Specify using a range of values.
Topics
Biology · Required Practicals · B2: Organisation · Required Practicals
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 1 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.