AQA GCSE Chemistry Chemistry Paper 2 (Higher), 2023: Question 4

✅ Correct Answer

Water vapour

💡 Key Knowledge

The three main greenhouse gases you must know for GCSE Chemistry are:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Water vapour (H₂O)

❌ Common Errors

Do not confuse greenhouse gases with the main elements in our atmosphere. Nitrogen (N₂) and Oxygen (O₂) make up 99% of the air but are not greenhouse gases because they do not absorb infrared radiation.

✅ Correct Answer (Option A)

• As population increases, more energy/transport is required [1 mark]
• This leads to more fossil fuels being burned [1 mark]

✅ Correct Answer (Option B)

• More agricultural land/space for housing is required [1 mark]
• This leads to increased deforestation (clearing forests) [1 mark]

🧠 Exam Technique

This is an "Explain" question worth 2 marks. You must link the cause directly to the effect:

"More people means..." → "which results in..."

Simply saying "people burn fossil fuels" is not enough for both marks. You must mention the increased demand for energy or space first!

✅ Correct Answer (Option A)

• An increased population means more food is required [1 mark]
• This leads to more methane-producing agriculture, such as beef cattle farming or rice fields [1 mark]

✅ Correct Answer (Option B)

• An increased population produces more waste [1 mark]
• This waste decomposes in landfill sites, releasing methane gas [1 mark]

💡 Key Knowledge

Methane (CH₄) is produced biologically. The two main human sources are:

• Digestive systems of livestock (especially cows).
• Anaerobic decay of organic waste in landfill sites and wet rice paddy fields.

✅ Correct Answer (Choose any TWO)

• Melting of polar ice caps / glaciers
• Rising sea levels
• Flooding of low-lying coastal areas
• Extremes of weather (e.g., severe droughts, storms)
• Loss of habitats and extinction of species

❌ Common Errors to Avoid

The examiner will NOT accept:

• "Global warming" (this is the cause, not the effect!)
• "Acid rain" (caused by sulfur dioxide, not greenhouse gases)
• "Global dimming" (caused by particulates)
• "Ozone layer damage" (caused by CFCs, not CO₂/CH₄)

✅ Correct Answer (Choose ONE)

• There may be other natural causes for temperature changes (e.g., historical ice age cycles).
• The Earth's climate is extremely complex and difficult to model accurately.

🧠 Exam Technique

Remember that in science, theories must be backed by peer-reviewed evidence. Because we cannot easily run controlled experiments on the entire planet, some scientists remain skeptical about simplified models of climate change.