AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Higher), 2023: Question 5

Mark scheme

Show the mark scheme

Question 5

AO /

Question Answers Extra information Mark

Spec. Ref.

05.1 any one from: 1 AO1

• melting ice 5.9.2.3

• rising sea levels

• flooding

• extremes of weather

• loss of habitats

ignore global warming

do not accept acid rain

do not accept global dimming

do not accept references to

ozone

AO /

Spec. Ref.

allow uv / ultra-violet for short

05.2 wavelength radiation AO1

5.9.2.1

allow ir / infra-red for long 5.9.2.3

wavelength radiation

ignore references to the ozone

layer

(greenhouse gases) allow short 1

wavelength radiation to enter

the atmosphere

(which are) absorbed by the 1

earth and re-emitted as longer

wavelength radiation

(which is) absorbed by 1

(greenhouse gases in) the

atmosphere

(this) increases the temperature– OMBINED SCIENCE: TRILOGY – 1 –

leading to global warming

AO /

Spec. Ref.

05.3 trees use carbon dioxide 1 AO2

5.9.1.3 15

(for) photosynthesis 1 5.9.1.4

(and) carbon dioxide causes allow (and) carbon dioxide is a 1

global warming greenhouse gas

Total Question 5 8

How to answer it

Global Warming and Climate Change

What this question tests

Knowledge of effects of climate change, understanding of how greenhouse gases cause global warming, and explaining how planting trees reduces warming by removing CO₂ through photosynthesis.

Question 05.1

Give one effect of global climate change. [1 mark]

✅ Correct answers

melting ice
rising sea levels
flooding
extremes of weather
loss of habitats

Any one of these gains the mark.

💡 Key knowledge

The question asks for an effect of climate change, not a cause. You only need one clear valid example.

🧠 Exam technique

For a 1-mark recall question, keep it short and precise. A single accepted effect is enough.

❌ Common errors

Writing global warming as the answer. The mark scheme says ignore this.
Giving unrelated ideas such as acid rain.
Talking about the ozone layer or global dimming, which are not accepted here.

Question 05.2

Explain how greenhouse gases cause global warming. [4 marks]

✅ Correct answer

Greenhouse gases allow short wavelength radiation to enter the atmosphere.

This radiation is absorbed by the Earth and re-emitted as longer wavelength radiation.

The longer wavelength radiation is absorbed by greenhouse gases in the atmosphere.

This increases the temperature, leading to global warming.

💡 Key knowledge

Short wavelength radiation from the Sun passes into the atmosphere.
The Earth absorbs this energy.
The Earth re-emits energy as longer wavelength infrared radiation.
Greenhouse gases absorb some of this outgoing infrared radiation.
This traps energy and increases temperature.

🧠 Exam technique

To reach 4 marks, your answer should follow the full chain in the correct order:

Short wavelength radiation enters.
Earth absorbs it and re-emits longer wavelength radiation.
Greenhouse gases absorb this longer wavelength radiation.
Temperature increases, causing global warming.

Top answers are clear, sequenced, and use the correct radiation words.

❌ Common errors

Mentioning the ozone layer. The mark scheme says to ignore references to ozone.
Saying greenhouse gases let in infrared rather than short wavelength radiation.
Missing out the idea that the Earth re-emits energy as longer wavelength radiation.
Saying greenhouse gases “make heat” instead of explaining that they absorb outgoing radiation.

📐 Mark breakdown

1 mark: greenhouse gases allow short wavelength radiation to enter the atmosphere
1 mark: radiation is absorbed by the Earth and re-emitted as longer wavelength radiation
1 mark: longer wavelength radiation is absorbed by greenhouse gases in the atmosphere
1 mark: temperature increases, causing global warming

Model 4-mark answer

Greenhouse gases allow short wavelength radiation from the Sun to enter the atmosphere. The Earth absorbs this radiation and re-emits it as longer wavelength infrared radiation. Greenhouse gases absorb some of this longer wavelength radiation in the atmosphere. This causes the Earth’s temperature to increase, leading to global warming.

Question 05.3

Explain how planting trees reduces global warming. [3 marks]

✅ Correct answer

Trees use carbon dioxide.

They use it for photosynthesis.

Carbon dioxide causes global warming because it is a greenhouse gas, so removing some CO₂ reduces global warming.

💡 Key knowledge

Trees take in CO₂ from the atmosphere.
They use CO₂ during photosynthesis to make glucose.
CO₂ is a greenhouse gas.
Less CO₂ in the atmosphere means less greenhouse effect and less global warming.

🧠 Exam technique

Do not stop at “trees absorb carbon dioxide.” To get full marks, link it to photosynthesis and then to reduced global warming.

❌ Common errors

Only saying “trees give out oxygen” — this does not answer the question fully.
Forgetting to mention photosynthesis.
Not linking CO₂ removal to the fact that CO₂ causes global warming.

📐 Mark breakdown

1 mark: trees use carbon dioxide
1 mark: for photosynthesis
1 mark: carbon dioxide causes global warming / is a greenhouse gas

Model 3-mark answer

Planting trees reduces global warming because trees use carbon dioxide for photosynthesis. Carbon dioxide is a greenhouse gas that causes global warming, so removing it from the atmosphere reduces the warming effect.

Examiner insight for the whole question

💡 What successful students did

Used precise climate-change effects in 05.1.
Explained the greenhouse effect in the correct sequence in 05.2.
Linked trees, photosynthesis, and CO₂ removal clearly in 05.3.

❌ Where students lost marks

Confusing climate change with ozone depletion.
Giving a vague answer like “the Earth gets hotter” without explaining why.
Not making the final link from CO₂ to global warming in the tree question.

🧠 Final exam tip

In explain questions, build a chain of cause and effect. Each sentence should lead to the next. That is often exactly how the marks are awarded in AQA mark schemes.

Topics

Chemistry · C9: Chemistry of the Atmosphere