AQA GCSE Biology Biology Paper 2 (Foundation), November 2021: Question 7

✅ Mark Scheme Breakdown (4 Marks)

You must describe two different patterns and give data for each:

• Pattern 1: Overall increase in CO₂ concentration [1 mark]
• Data 1: Increased from 364 to 418 arbitrary units (allow 357 to 422) OR an overall increase of 54 units (allow 45 to 65 units) [1 mark]
• Pattern 2: Regular fluctuations / annual cycles (peaks and troughs) [1 mark]
• Data 2: Each cycle repeats every 1 year (or 5 cycles every 5 years) OR the variation per cycle is 8 to 16 arbitrary units [1 mark]

🧠 Exam Technique: "Dual-Trend" Graphs

• Look for the 'macro' and 'micro': Whenever a line graph shows a jagged line pointing upwards, there are always two patterns:
  1. The overall long-term trend (macro)
  2. The repeating oscillations/seasonality (micro)
• Always pair descriptions with numbers: A description without figures can only get half marks. State units (here, "arbitrary units" and "years").

📐 Step-by-Step Data Reading

1 Identify the overall trend endpoints:
Start (1988): ~364 arbitrary units.
End (2014): ~418 arbitrary units.
Net increase = 418 − 364 = 54 arbitrary units.

2 Identify the cycle length:
Count peaks between 1990 and 2000 = 10 peaks in 10 years.
Therefore, 1 cycle occurs per 1 year.

❌ Common Errors to Avoid

• Describing only one pattern: Giving two data points for the overall rise only counts as one pattern + data (maximum 2 marks).
• Missing the annual cycle: Calling the line "bumpy" or "unreliable" instead of describing it as periodic peaks and troughs.
• Omitting axis units: Just writing "went up by 54" without reading the axis label ("arbitrary units").

✅ Acceptable Answers (Any Two, 1 Mark Each)

• Combustion / burning of fossil fuels (e.g. coal, oil, petrol in cars, gas in power stations).
• Deforestation (clearing land for farming/cattle reduces photosynthesis and releases CO₂ when wood is burned or decays).
• Planting trees / afforestation (human activity that decreases atmospheric CO₂).
• Farming / agriculture (e.g. burning slash-and-burn waste).

💡 Key Knowledge: The Carbon Cycle

• Combustion: Fossil fuel + Oxygen → CO₂ + Water
• Deforestation: Fewer trees mean less CO₂ is locked away by photosynthesis.
• Note: The question asks for activities that affect CO₂, so actions that reduce it (like afforestation) are equally credited.

❌ Common Errors

• Vague answers: Writing simply "factories" or "pollution" without specifying combustion or emissions scores 0 marks.
• Confusing gases: Mentioning CFCs, the ozone layer, or acid rain. Keep it strictly focused on carbon dioxide!
• "Breathing": Respiration is a biological life process, not typically credited as a distinct industrial/human activity (though the mark scheme permits it only as a last resort for 1 mark if nothing else is given).

✅ Model Answer (Level 2: 3–4 Marks)

An increasing concentration of carbon dioxide enhances the greenhouse effect, leading to global warming (rising global temperatures).

This affects organisms in several linked ways:

• Loss of habitat & ice melt: Rising temperatures melt polar ice caps and cause sea levels to rise, destroying habitats for species like polar bears and leading to potential extinction.
• Extreme weather & drought: Changed rainfall patterns cause severe droughts and desertification, meaning many plant and animal species die out due to water and food shortages.
• Migration & distribution: Warmer climates cause organisms (e.g. insects, birds) to migrate towards the poles or change their geographical ranges, potentially spreading vector-borne diseases.
• Plant growth: Higher CO₂ levels and warmer temperatures may initially increase the rate of photosynthesis in some crop plants, altering competitive balances.

🧠 Exam Technique: Securing Level 2 (3–4 Marks)

• Cause → Mechanism → Effect: Don't just list facts! Connect them logically:
  CO₂ rises → Global warming → Ice melts → Polar bears lose hunting grounds → Population decline / Extinction.
• Level 1 (1–2 marks): Points stated simply with no linked biological reasoning (e.g., "it gets hotter and animals die").
• Level 2 (3–4 marks): Multiple relevant points identified and logically linked to explain consequences on living organisms.

❌ Major Misconceptions

• Ozone layer confusion: Claiming that CO₂ destroys the ozone layer or allows harmful UV radiation in. This is scientifically incorrect and scores 0.
• Suffocation myth: Stating that animals won't have enough oxygen to breathe because there is too much CO₂. Atmospheric CO₂ is only around 0.04%.
• Missing the organism link: Explaining that "sea levels will rise" without stating how that harms living organisms (e.g. loss of coastal habitats, loss of food sources).