AQA GCSE Biology Biology Paper 2 (Higher), June 2022: Question 4

✅ Acceptable Answers (Any One)

• Carbon dioxide (CO₂)
• Acidic gases: Sulfur dioxide (SO₂) or Nitrogen oxides (NOₓ)
• Particulates / smoke / soot
• Carbon monoxide (CO)
• Methane (CH₄)
• CFCs (chlorofluorocarbons)

🧠 Exam Technique

The prompt asks for one substance. Do not give a long list; if you give two answers and one is incorrect, you risk cancelling out your mark.

✅ Acceptable Answers (Any Three)

• Fertiliser (or nitrates / phosphates)
• Sewage (or human waste / faeces / urine / urea / organic matter)
• Toxic chemicals (e.g., heavy metals like mercury, or sulfur dioxide / acid rain)
• Herbicides
• Fungicides
• Insecticides / Pesticides
• Oil
• Radioactive / nuclear waste

❌ Common Errors & Command Traps

• Ignoring the restriction: Writing "plastic bottles" or "litter" scores 0 marks because the question explicitly excludes them.
• Vague grouping: Writing "weedkiller, bug spray, and pesticides" counts as only one pesticide group mark unless named specifically (herbicide, insecticide, fungicide).
• Vague words: Words like "chemicals", "dirt", or "poisons" are too unspecific to gain credit.

💡 Key Points: Air Pollution

• Greenhouse gases (CO₂ / Methane): Trap infrared radiation / heat → causes global warming & climate change → rising sea levels, severe weather, habitat loss, altered migration.
• Acidic gases (SO₂ / NOₓ): Dissolve in rain forming acid rain → damages leaf cuticles (reducing photosynthesis) → leaches minerals from soil → causes respiratory irritation/asthma in humans.
• Carbon monoxide (CO): Binds irreversibly with haemoglobin → reduces oxygen carrying capacity of blood → suffocation/death.
• Particulates / Soot: Coats leaves blocking sunlight (less photosynthesis) → enters human lungs causing bronchitis and breathing difficulties.

💡 Key Points: Water Pollution

• Fertiliser run-off (Eutrophication): Excess nitrates cause rapid algal growth (bloom) → algae block light, underwater plants die → bacteria multiply to decompose dead plants → bacteria consume dissolved oxygen in aerobic respiration → fish suffocate and die.
• Untreated sewage: Bacteria feed on organic waste and multiply → aerobic respiration uses up oxygen → aquatic organisms die. Sewage also introduces pathogens (causing cholera/dysentery).
• Toxic chemicals / Heavy metals: Cause bioaccumulation along food chains → toxic buildup damages cellular metabolism (protein synthesis/respiration) in apex predators and humans.

🎯 Model 6-Mark Answer Template

Air pollution:
Sulfur dioxide dissolves in cloud water to form acid rain, which damages tree leaves and lowers soil pH, preventing plants from absorbing mineral ions. In humans, particulates and acidic gases irritate the lungs, triggering asthma. Carbon dioxide traps heat in the atmosphere, leading to global warming and loss of species habitats.

Water pollution:
Fertilisers washed into rivers cause rapid algal blooms that block sunlight, causing submerged plants to die. Decomposer bacteria break down dead plant matter and reproduce rapidly, using up dissolved oxygen through aerobic respiration; this lack of oxygen causes fish to die. In addition, toxic chemicals like mercury bioaccumulate up food chains, causing organ damage to top predators.

❌ What Keeps Students in Level 1 (1–3 Marks)

• Vague effects: "Pollution is bad for trees and kills animals" (no mechanism given).
• One-sided answers: Only discussing air pollution while completely ignoring water (or vice versa) caps you at 3 marks.
• Eutrophication confusion: Claiming that "algae eat all the oxygen" or "fertiliser poisons the fish directly". You must mention decomposer bacteria respiring aerobically.