AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2021: Question 3
13 marks · Standard Demand difficulty · Short Answer
Analyze anaerobic respiration in yeast and animal cells, including experimental data interpretation and enzyme activity.
Practise this questionQuestion
Question text
03 Anaerobic respiration in yeast is called fermentation.
The equation for fermentation is:
glucose → ethanol + carbon dioxide
03.1 How does the equation show that fermentation is an anaerobic reaction?
[1 mark]
Fermentation in yeast is used in the manufacture of beer, wine and bread.
03.2 Why is fermentation used when making beer and wine?
[1 mark]
03.3 Explain why fermentation is used when making bread.
[2 marks]
A student investigated fermentation in yeast.
Figure 3 shows the apparatus.
Figure 3
This is the method used.
1. Mix yeast with sugar solution in a flask.
2. Put the flask in a water bath at 35 °C.
3. After 10 minutes attach a gas syringe to the flask.
4. Record the volume of carbon dioxide collected every 5 minutes for 1 hour.
03.4 What volume of carbon dioxide has been collected in the gas syringe in Figure 3?
[1 mark]
Volume of carbon dioxide = cm3
03.5 Why did the student wait 10 minutes before attaching the gas syringe?
[1 mark]
Tick ( ) one box.
To allow time for the mixture to reach 35 °C
To allow time for the sugar to dissolve
To allow time to draw a results table14
Figure 4 shows the results.
*13* Figure 4
03.6 A and B are different parts of the graph in Figure 4.
Draw one line from each part of the graph to the description of the reaction.
[2 marks]
Part of the graph Description of the reaction
Carbon dioxide is
not being produced
A
Carbon dioxide production is
fastest
B
Carbon dioxide production is
16 slowing down
*14* The equation for fermentation is repeated here.
glucose → ethanol + carbon dioxide
03.7 Suggest one reason why fermentation in the flask stopped.
[1 mark]
03.8 Fermentation is controlled by enzymes.
The investigation was repeated at 2 °C and at 75 °C.
No carbon dioxide was produced at either of these temperatures.
Suggest why no carbon dioxide was produced at 2 °C or at 75 °C.
[2 marks]
Reason at 2 °C
Reason at 75 °C
03.9 Anaerobic respiration also happens in animal cells.
Complete the equation for anaerobic respiration in animal cells.
Choose answers from the box.
[2 marks]
carbon dioxide ethanol glucose lactic acid water
→
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 no oxygen (reacting with the ignore there is no air 1 AO2
glucose) 4.4.2.1
03.2 produces ethanol / alcohol 1 AO1
4.4.2.1
03.3 produces carbon dioxide / gas 1 AO1
(which) makes the bread / allow idea related to making the 1 AO2
dough rise bread lighter or affecting its
texture 4.4.2.1
03.4 45 (cm3) 1 AO2
4.4.2.1
03.5 to allow time for the mixture to 1 AO3
reach 35 °C 4.4.2.1
03.6 AO3
4.4.2.1
do not accept more than one line from a box on the left
03.7 any one from: 1 AO2
• glucose / sugar / food ran out 4.4.2.1
• ethanol / alcohol killed the ignore yeast / cells died
cells / yeast unqualified
ignore produced ethanol /
alcohol unqualified
03.8 (2 °C) too cold (for enzymes / allow yeast / enzyme was 1 AO2
yeast to work) inactive 4.2.2.1
ignore yeast killed 4.4.2.1
allow no / few successful
collisions
do not accept enzymes are
denatured
(75 °C) enzymes denatured allow enzymes destroyed 1
allow description eg change in
shape of active site or of
enzyme
allow yeast killed
do not accept enzymes killed
ignore references to collisions
unqualified
03.9 glucose → lactic acid 1 mark for each chemical 2 AO1
must be in this order 4.4.2.1
ignore formulae
Total 13
How to answer it
Yeast Fermentation & Respiration
What this question tests
This question assesses your understanding of anaerobic respiration in different organisms. You need to know the products of fermentation in yeast, how temperature affects enzyme-controlled reactions, and how to interpret experimental data from graphs and equipment.
The Basics of Fermentation
💡 Key Knowledge
- Anaerobic means "without oxygen".
- In yeast: Glucose → Ethanol + Carbon Dioxide.
- In animals: Glucose → Lactic Acid.
🧠 Exam Technique
When asked "how the equation shows" something, look only at the words in the equation. If oxygen isn't a reactant, it's anaerobic!
03.1 Why is it anaerobic?
1 Mark
03.2 & 03.3 Uses in Food & Drink
Bread: It produces carbon dioxide 1 Mark which makes the dough rise. 1 Mark
❌ Common Errors
Don't say "it produces air" for bread. You must name the specific gas: Carbon Dioxide. Also, avoid saying "it makes the bread grow"—the correct term is rise.
Data and Graphs
📐 Reading the Scale
Look at the gas syringe in Figure 3:
- Identify the major marks: 40 and 50.
- Count the small intervals: There are 5 gaps between 40 and 50.
- Each small mark = 2 cm³.
- The plunger is exactly halfway between 40 and 50.
- Result: 45 cm³
🧠 Interpreting Gradients
- Steepest line: Reaction is fastest.
- Curving line: Reaction is slowing down.
- Flat horizontal line: Reaction has stopped.
03.6 Matching the Graph
- Part A: Carbon dioxide production is fastest (steepest part of the curve).
- Part B: Carbon dioxide is not being produced (the line is flat/horizontal).
Enzymes and Limiting Factors
💡 Why do reactions stop?
In a closed flask of yeast and sugar, the reaction stops because:
- The glucose (food) runs out.
- The ethanol concentration becomes high enough to kill the yeast.
03.8 Temperature Effects
At 2 °C
It is too cold for the enzymes to work / the yeast is inactive.
1 MarkAt 75 °C
The enzymes have denatured.
1 Mark❌ Common Errors
Never say enzymes "die" or "freeze". Enzymes are molecules, not living things. At high temperatures, they denature (the active site changes shape). At low temperatures, they are simply inactive or have low kinetic energy.
Anaerobic Respiration in Animals
The Equation
glucose → lactic acid
2 Marks (1 for each correct term in order)🧠 Key Distinction
Students often lose marks by adding "carbon dioxide" to the animal equation. Remember: Only yeast/plants produce CO₂ during anaerobic respiration. Animals produce only lactic acid.
Final Examiner Tip
This question often appears to test if you can distinguish between yeast and human respiration. Use this table to keep them straight:
| Organism | Products |
|---|---|
| Yeast | Ethanol + CO₂ |
| Animal | Lactic Acid |
Topics
Biology · B2: Organisation · B4: Bioenergetics
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 1 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.