AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2020: Question 3

✅ Correct answer

The variety of all the different species of organisms on Earth
or
The variety of all the different species of organisms in a habitat / area / ecosystem

💡 Key knowledge

• Biodiversity means the number and variety of different species.
• It can be described globally or in one habitat.

🧠 Exam technique

• Use the exact science idea: variety of species.
• For a 1-mark definition, keep it short and precise.

❌ Common errors

• Writing different animals only — too narrow.
• Talking about habitats without mentioning species variety.
• Saying number of organisms instead of variety of species.

✅ Correct answers

• Compost
• Burning
• As a fuel

💡 Key knowledge

• Peat is often used by humans for gardening or as fuel.
• The mark scheme also allows the idea that peat can improve soil or help grow plants/crops.

🧠 Exam technique

• Give one clear use only.
• Plain keywords are enough: compost or fuel.

❌ Common errors

• Saying fertiliser may be too vague if not linked to a valid use.
• Giving a reason like for farming without naming the actual use.

✅ Correct answer

Decay / burning of peat releases carbon dioxide into the atmosphere, which increases global warming.

💡 Key knowledge

• Peat stores carbon, so peat bogs act as a carbon sink / carbon store.
• When peat is destroyed, this stored carbon can be released as CO₂.
• CO₂ is a greenhouse gas and contributes to global warming.

🧠 Exam technique

• Write a cause-and-effect chain: peat is burned/decays → CO₂ released → global warming increases.
• The question says do not refer to biodiversity, so avoid that completely.

❌ Common errors

• Saying only it harms the environment — too vague.
• Talking about habitat loss or biodiversity — not allowed here.
• Forgetting to mention carbon dioxide.

✅ Correct answers

• Takes minerals from the soil as crops are harvested/removed.
• Leads to soil erosion.
• Farmers have to use fertilisers which pollute water (streams/lakes).
• Burning crop waste produces carbon dioxide.
• Using large farm machinery causes soil compaction.

💡 Key knowledge

• Intensive farming means growing one crop repeatedly on large areas.
• Harvesting crops removes nutrients/minerals from the soil.
• Heavy machinery can squash soil particles together, making it harder for water and air to move through.
• Fertiliser runoff can pollute rivers and lakes.

🧠 Exam technique

• Because it is worth 2 marks, give two separate environmental effects.
• Use clear science words such as soil erosion, pollution, compaction, or carbon dioxide.

❌ Common errors

• Writing it reduces biodiversity — the question says do not refer to biodiversity.
• Writing nutrients alone without explaining they are lost from the soil.
• Using the same idea twice, e.g. pollution and water pollution.

✅ Correct answer

Antibiotics pass into the environment in animal faeces / urine / sewage or into rivers.
Bacteria in water or on land become antibiotic resistant.
Some of these bacteria are human pathogens.
So they cause human diseases which cannot be cured because they are antibiotic resistant.

💡 Key knowledge

• Using antibiotics widely creates strong selection pressure for resistant bacteria.
• Resistant bacteria can survive and reproduce.
• Some resistant bacteria are pathogens that infect humans.
• These infections are harder or impossible to treat with normal antibiotics.

🧠 Exam technique

• To get full marks, explain the sequence:
  antibiotics used in farming → bacteria exposed → resistance develops → resistant human pathogens spread → disease harder to cure
• Use linking words like therefore, so, and because.
• One mark can be gained for mentioning antibiotics in meat/milk being eaten by humans, but the stronger answer is the resistance chain.

❌ Common errors

• Only saying antibiotics are bad — too vague.
• Not mentioning resistance.
• Stopping at bacteria become resistant without saying why this threatens humans.
• Forgetting that the bacteria can be human pathogens.

🧠 How to secure marks

• 1-mark definition: give a precise science phrase.
• 2-mark explanation: give two linked points.
• 4-mark explanation: write a full chain of cause and effect.

📐 Not a calculation question, but still be precise

• Use correct terms such as carbon dioxide, global warming, soil erosion, and antibiotic resistance.
• Do not waste time with extra detail that is not asked for.
• Read the command word carefully: define, give, explain, suggest.