AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2024: Question 4
13 marks · Low Demand difficulty · Short Answer
Describe changes in atmospheric nitrogen from a graph, recall details of photosynthesis, and identify properties of naturally occurring polymers including DNA and glucose polymers.
Practise this questionQuestion
Question text
04 This question is about the Earth’s atmosphere and naturally occurring polymers.
04.1 Figure 5 shows how the estimated percentage of nitrogen in the Earth’s atmosphere
has changed since the Earth was formed.
Figure 5
Describe the trends shown by the graph.
Use data from Figure 5.
[3 marks]
The percentage of oxygen in the Earth’s atmosphere has increased since the Earth
was formed.
This is because of photosynthesis.
The word equation for the photosynthesis reaction is:
carbon dioxide + water → glucose + oxygen
04.2 What happened to the percentage of carbon dioxide in the atmosphere when
photosynthesis began?
[1 mark]
Tick ( ) one box.
The percentage of carbon dioxide decreased.
The percentage of carbon dioxide stayed the same.
The percentage of carbon dioxide increased.
04.3 The photosynthesis reaction takes in energy from the surroundings.
Complete the sentence.
Choose the answer from the box.
[1 mark]
carbon dioxide light water
The source of the energy used in photosynthesis is17 .
04.4 Which two produce oxygen by photosynthesis?
[2 marks]
Tick ( ) two es.
Algae
Animals
Plants
Viruses
Yeast
04.5 The glucose produced during photosynthesis can form naturally occurring polymers.
Which two are naturally occurring polymers that can be produced from glucose?
[2 marks]
Tick ( ) two es.
Cellulose
DNA
Poly(propene)
Protein
Starch 18
DNA molecules contain two polymer chains.
A DNA molecule has a relative formula mass (Mr) of approximately 140 000 000 000
04.6 What is the approximate relative formula mass (Mr) of the DNA molecule in
standard form?
[1 mark]
Tick ( ) one box.
1.4 × 109
*17* 10
1.4 × 10
1.4 × 1011
1.4 × 1012
04.7 What is the approximate relative formula mass (Mr) of each polymer chain in the
DNA molecule?
[1 mark]
Tick ( ) one box.
70 000 000 000
140 000 000 000
280 000 000 000
560 000 000 000
04.8 Complete the sentence.
[1 mark]
The shape of a DNA molecule is a double19 .
04.9 How many different nucleotides are present in a molecule of DNA?
[1 mark]
Tick ( ) one box.
*18* 1
Mark scheme
Show the mark scheme
Question 4
AO /
Question Answers Extra information Mark
Spec. Ref.
04.1 percentage of nitrogen 1 AO2
increases 4.9.1.2
until 2.3 billion years allow a value in the range 2.1 to 1
2.4 billion years
allow until 80%
then remains constant 1
AO /
Spec. Ref.
04.2 the percentage of carbon 1 AO1
dioxide decreased 4.9.1.4
AO /
Spec. Ref.
04.3 light 1 AO1
4.9.1.3
AO /
Spec. Ref.
04.4 algae 1 AO1
4.9.1.3
plants 1
AO /
Spec. Ref.
04.5 cellulose 1 AO1
4.7.3.4
starch – – 1 –
AO /
Spec. Ref.
11 13
04.6 1.4 × 10 1 AO2
4.3.1.2
4.7.3.4
AO /
Spec. Ref.
04.7 70 000 000 000 1 AO2
4.7.3.4
AO /
Spec. Ref.
04.8 helix 1 AO1
4.7.3.4
AO /
Spec. Ref.
04.9 4 1 AO1
4.7.3.4
Total Question 4 13
How to answer it
Earth's Atmosphere & Naturally Occurring Polymers
📋 What this question tests
This question assesses key foundational ideas from AQA GCSE Chemistry: The Earth's Atmosphere (Topic 9) and Organic Chemistry: Synthetic & Naturally Occurring Polymers (Topic 7). You are tested on:
- Describing graph trends using data and identifying plateaus (nitrogen accumulation).
- Understanding how photosynthesis by plants and algae altered early atmospheric gases (decreasing CO₂ and producing O₂).
- Identifying natural polymers formed from glucose (starch and cellulose).
- Recalling the core structural features of DNA (double helix, 4 distinct nucleotides) and carrying out standard form and proportional mass calculations.
Describing Atmospheric Nitrogen Trends
Data interpretation: Percentage of nitrogen vs. age of the Earth
✅ Correct Answer Breakdown
A full 3-mark response requires three clear features:
- Trend 1: The percentage of nitrogen increases / rises. [1 mark]
- Turning point: Until 2.3 billion years (allow values from 2.1 to 2.4 billion years, or stating "until 80%"). [1 mark]
- Trend 2: It then remains constant / levels off / stays the same. [1 mark]
🧠 Exam Technique: Two-Phase Graphs
Whenever a line graph curves and flattens out, you must describe both phases plus the inflection point:
- What happens first? (increases rapidly)
- Where does the change happen? (at 2.3 billion years)
- What happens after that? (stays flat at 80%)
❌ Common Errors
- Writing just "it goes up" without stating that it eventually levels off.
- Failing to quote data from the horizontal axis (e.g. omitting 2.3 billion years).
- Saying nitrogen reaches 100% (the plateau is at 80%, corresponding to today's atmosphere).
Photosynthesis and the Evolution of the Atmosphere
Word equation provided: carbon dioxide + water → glucose + oxygen
✅ Correct Answers
04.2 (1 mark): What happened to atmospheric CO₂?
☑ The percentage of carbon dioxide decreased.
04.3 (1 mark): Source of energy for photosynthesis:
light (taken in from surroundings)
04.4 (2 marks): Two organisms producing O₂ via photosynthesis:
☑ Algae [1 mark]
☑ Plants [1 mark]
💡 Key Knowledge
- Early Earth: The atmosphere was mainly CO₂ with little to no O₂.
- Algae first evolved around 2.7 billion years ago; photosynthesis took in CO₂ and released O₂.
- Over the next billion years, green plants evolved, further decreasing CO₂ and increasing O₂ to levels that enabled animals to evolve.
- Photosynthesis is endothermic—it absorbs energy transferred by light.
❌ Common Errors
- Ticking Yeast: Yeast is a fungus; it respires (often anaerobically) and produces CO₂, not oxygen.
- Ticking Viruses: Viruses are non-cellular entities that cannot carry out metabolic processes like photosynthesis.
Naturally Occurring Polymers from Glucose
Identifying condensation polymers made from sugar monomers
✅ Correct Answers
Tick two boxes:
☑ Cellulose [1 mark]
☑ Starch [1 mark]
💡 Key Knowledge: Natural Polymers
| Polymer | Monomer |
|---|---|
| Starch & Cellulose | Glucose (monosaccharide) |
| Proteins | Amino acids |
| DNA | Nucleotides |
| Poly(propene) | Propene (synthetic addition polymer) |
DNA Relative Formula Mass (Mᵣ) & Standard Form
Data: A DNA molecule has Mᵣ ≈ 140 000 000 000 and contains two chains
📐 Step-by-Step Calculations
04.6 Standard Form Conversion:
- Number: 140 000 000 000
- Place the decimal point between 1 and 4: 1.4
- Count places shifted to the left: 11 places.
- Result: 1.4 × 10¹¹
04.7 Mass of Each Polymer Chain:
- DNA consists of two polymer chains.
- Mass per chain = 140 000 000 000 ÷ 2
- Result = 70 000 000 000
❌ Common Errors
- Counting zeros instead of powers: There are 10 zeros in 140 000 000 000, so students mistakenly select 1.4 × 10¹⁰. Remember that the "4" also counts as a place shift!
- Multiplying instead of dividing in 04.7: Doubling to 280 000 000 000 instead of halving for an individual chain.
Structure of DNA
Core recall facts about the double helix and nucleotides
✅ Correct Answers
04.8 (1 mark): The shape of a DNA molecule is a double ________.
helix
04.9 (1 mark): Number of different nucleotides in a DNA molecule:
☑ 4
💡 Key Knowledge: DNA Specifications
- DNA (Deoxyribonucleic acid) encodes genetic instructions for development and functioning of living organisms.
- Most DNA molecules are two polymer chains made from four different monomers called nucleotides (bases A, T, C, G).
- The two strands wrap around each other to form a double helix structure.
Topics
Chemistry · C7: Organic Chemistry · C9: Chemistry of the Atmosphere
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Foundation), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.