AQA AS Level Biology Paper 2, November 2021: Question 5
9 marks · Medium difficulty · Practical Techniques & Data Analysis
Analyze an experiment investigating amylase activity using starch-agar plates, including enzyme action, controls, biochemical testing, and dilution calculations.
Practise this questionQuestion
Question text
05 A student investigated the activity of the enzyme amylase. He cut three identical wells
(D, E and F) in starch-agar in a Petri dish. He added 0.2 cm of:
• amylase solution to well D
• boiled amylase solution to well E
• water to well F.
After 60 minutes, he covered the starch-agar with iodine solution.
Figure 7 shows his results.
Figure 7
05.1 Explain the appearance of the agar in the clear area surrounding well D.
[2 marks]
05.2 What can you conclude about the activity of amylase from the appearance of the agar
surrounding well E and well F in Figure 7?
[2 marks]
05.3 The student cut out a piece of agar from the clear area surrounding well D. He
obtained a solution of the substances contained in this piece of agar.
Describe a different biochemical test the student could use with this solution to
confirm that amylase had affected the starch in the clear area surrounding well D.
[2 marks]
The diameter of the clear area around well D is 18 mm
In a different investigation, the student prepared a dilution of the amylase solution. He
did this by mixing amylase solution and water in the volumes shown in Table 1.
Table 1
Amylase solution / cm3 Water / cm3
1.6 2.4
He prepared a starch-agar Petri dish identical to Figure 7, but with a single well. He
added 0.2 cm3 of the diluted amylase solution to this well and left the Petri dish for
60 minutes.
05.4 Use all of this information to predict the diameter of the clear area that will form around
the well containing the diluted amylase solution.
Give your answer to the nearest whole number.
Show your working.
[2 marks]
Answer mm
05.5 The student used a ruler to measure the diameter in mm of the clear area around
well D in Figure 7.
Use this information to explain why the answer to Question 05.4 should be given to
the nearest whole number.
[1 mark]
Mark scheme
Show the mark scheme
05.1 1. Amylase hydrolyses starch;
2. (To) maltose;
Question Marking Guidance Mark Comments
05.2 1. (E) Amylase/enzyme is denatured; 1. Accept a
description of
2. (F) amylase is needed for/causes starch denaturation
hydrolysis/breakdown/digestion
OR 2. Ignore ‘it is a
control’
(F) water (alone) does not (cause starch)
hydrolysis/breakdown/digestion;
05.3 1. Heat in Benedict’s (solution); 1. Reject description
of non-reducing
2. Red/green/orange (precipitate/colour) (shows 2 sugar test
maltose/reducing sugar); 2. Accept for ‘heat’,
water bath
05.4 Correct answer for 2 marks = 7;;
Accept for 1 mark,
7.2 (correct answer but not rounded)
OR
Evidence of 1.6 ÷ 4.0/0.4/40% (correct dilution
factor)
OR
Evidence of 0.08 (correct amylase volume in
0.2cm3)
1. Reduces (human) error/uncertainty;
05.5 Ignore can only
2. (It is) the resolution of a ruler; measure to whole
numbers
3. (For a ruler measurement) the uncertainty is 1 max
±1(mm) Ignore reliability and
– LOGYprecision– – JUNE 2021
OR
(For a ruler measurement) the true value lies Accept, the 11
with ±1(mm); uncertainty of a ruler
reading is (±)0.5(mm)
OR readings of <1mm
are not accurate
TOTAL 9
How to answer it
Amylase Activity Investigation Study Guide
What this question tests
This multi-part practical question assesses your understanding of enzyme action (hydrolysis of starch), the role of controls in biological experiments, biochemical testing for reducing sugars, dilution calculations, and the evaluation of measurement uncertainties and instrument resolution.
Explaining the Clear Area Around Well D
✅ Correct Answer
- Amylase hydrolyses starch.
- Produces maltose (or breaks down starch into smaller sugars).
💡 Key Knowledge
Starch turns blue-black with iodine solution. Where active amylase diffuses out of well D, it breaks down the surrounding starch via hydrolysis. The resulting sugars do not give a blue-black colour with iodine, leaving a visible clear halo.
🧠 Exam Technique
Be precise with biological terminology. Use key scientific verbs like hydrolyses instead of vague terms like "destroys" or "eats".
Conclusions from Wells E and F (Controls)
✅ Correct Answer
- Well E: Amylase/enzyme is denatured (so no clear area forms).
- Well F: Water alone does not cause starch hydrolysis / amylase is needed for starch breakdown.
❌ Common Errors
Students often lose marks by simply stating "Well E is a control" without explaining what that control proves (i.e., that high temperatures denature the tertiary structure of the enzyme, rendering its active site non-complementary).
Biochemical Testing for Starch Breakdown
✅ Correct Answer
- Add Benedict's solution and heat (in a water bath).
- Observe a colour change to brick-red / orange / green (indicating the presence of reducing sugars/maltose).
🧠 Exam Technique
The question specifies confirming that amylase affected the starch in the clear area. Since starch was digested into maltose, you must test for the product (reducing sugar) using Benedict's test. Reject any mention of the non-reducing sugar test.
Predicting Clear Area Diameter (Calculation)
📐 Step-by-Step Calculation
- Find total volume of dilution: 1.6 cm³ (amylase) + 2.4 cm³ (water) = 4.0 cm³.
- Calculate dilution factor: 1.6 ÷ 4.0 = 0.4 (or a 40% concentration solution).
- Scale original diameter: Original diameter with undiluted amylase = 18 mm.
- Predict new diameter: 18 mm × 0.4 = 7.2 mm.
- Round to required format: To the nearest whole number = 7 mm .
❌ Common Calculation Traps
Don't forget to divide by the total volume of the mixture (4.0 cm³), not just the volume of water! Failing to round to the nearest whole number as requested will also drop an intermediate mark.
Evaluating Measurement Resolution
✅ Correct Answer
- Matches the resolution/uncertainty of a standard ruler (which has a measurement uncertainty of ±1 mm).
- Reduces human error/uncertainty in recording decimal places beyond the instrument's capability.
💡 Key Knowledge
A standard laboratory ruler measures to the nearest millimeter (1 mm). Quoting a calculated value like 7.2 mm implies a level of precision that the measuring instrument cannot physically support.
Topics
Biology · Practical skills · Required Practicals · 3.1 Biological molecules · Data analysis · Uncertainty and evaluation · AS practicals (1–6)
Question and mark scheme from the AQA AS Level Biology examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.