AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2022: Question 2

AQA GCSE Combined Science: Trilogy

How human activities pollute rivers, lakes and seas

6 marks • Level of response

What this question tests

You need to explain different ways humans pollute water and link each cause to its effect. Top answers mention more than one type of pollution, use clear chains like fertilisers → algae → less light/oxygen → animals die , and show accurate science vocabulary.

Question focus

Explain how human activities are polluting rivers, lakes and seas. This is a 6-mark extended response, so you need several relevant points that are linked logically.

Mark scheme summary

Level 3: 5–6 marks

Relevant points are given in detail and are logically linked into a clear account.

Level 2: 3–4 marks

Relevant points are identified, with some linking, but the explanation may be incomplete or unclear.

Level 1: 1–2 marks

Simple points only, with little or no logical linking.

Examiner insight: what gets the top level?

Students scored best when they covered different sources of pollution, not just one.
Strong answers linked cause → effect → consequence.
Top responses often included sewage, fertilisers, toxic chemicals, plastics, and explained why these harm organisms.
To reach Level 3, students needed to consider different types of pollution, not just one example repeated in different words.

Part (a) — Explain how human activities pollute water

✅ Correct answer ideas

1. Sewage and waste water

Sewage can be released into rivers, lakes or seas.
It can contain pathogens, which can make animals and humans ill.
Sewage may also add nutrients that cause algae to grow rapidly.

2. Fertilisers from farms

Fertilisers can leach or run off into water.
They provide nutrients for algae, causing an algal bloom.
The algae block light, so plants die.
Dead plants and algae are decomposed by bacteria, which use up oxygen, so fish and other aquatic organisms may die.

3. Pesticides, herbicides and toxic chemicals

These can wash into water from farms, factories or power stations.
They are poisonous and can build up in food chains.
Some chemicals may cause mutations or act like hormones.

4. Litter and plastics

Plastic waste can be thrown into rivers, lakes and seas.
Plastics are often not biodegradable, so they stay in the environment for a long time.
Animals may swallow plastics or get them stuck around beaks, causing injury or death.
Microplastics can also build up in water animals.

5. Oil spills and other industrial pollution

Oil can leak from tankers, rigs or extraction sites.
This pollutes seawater and can harm wildlife.
Some industrial waste may also contain toxic substances or radiation leaks.

6. Acidification

Acid rain can make lakes more acidic.
Increased carbon dioxide in the atmosphere can also cause ocean acidification.
This changes water conditions and can harm aquatic organisms.

💡 Key knowledge

Run-off = rain washes substances from land into rivers/lakes/seas.
Leaching = chemicals dissolve and are carried through soil into water.
Algal bloom = rapid growth of algae due to extra nutrients.
Eutrophication chain = fertiliser → algae grow → light blocked → plants die → decomposers respire → oxygen falls → fish die.
Biodegradable means can be broken down naturally by microorganisms; most plastics are not.

🧠 Exam technique

For 6 marks, aim for 3–4 separate pollution examples with explanation.
Use linking words: because , therefore , this leads to , so .
Each example should show the human activity and the damage caused.
Try to include at least one example from farming, one from industry, and one from waste.

❌ Common errors

Only naming pollution types with no explanation.
Saying “pollution kills animals” without saying how.
Mixing up fertilisers and pesticides.
Forgetting that algal blooms can cause oxygen depletion.
Writing about land pollution only, with no link to water.
Not mentioning that plastics are not biodegradable.

📐 Best full-mark style answer

Human activities pollute water in several ways. Sewage can be released into rivers and seas and may contain pathogens, which can spread disease. Fertilisers from farms can wash into water and cause algae to grow rapidly. The algae block light, so plants die, and when the dead plants and algae decompose, oxygen is used up, which can kill fish. Pesticides and other toxic chemicals can also run into water from farms or industry and build up in food chains, harming animals. Plastic litter is often not biodegradable, so it remains in the water and can be swallowed by animals or trapped around them. Oil spills and acid rain can also damage aquatic habitats and kill organisms.

Why this would score highly: it covers different sources of pollution, includes clear chains of explanation, and ends with the effect on organisms.

How marks are awarded

To reach 1–2 marks

Give simple relevant statements, such as “fertilisers cause algae to grow” or “plastic is harmful to wildlife”.

To reach 3–4 marks

Add some explanation: “fertilisers cause algal blooms, which block light and reduce oxygen.”

To reach 5–6 marks

Cover several different pollution types and link them into a clear, detailed answer.

Memory help: easy chain to remember

Farming: fertiliser → algae bloom → light blocked → plants die → decomposition uses oxygen → fish die
Waste: plastics dumped → not biodegradable → animals ingest/entangled → harmed or die
Industry: toxic chemicals/oil → water contaminated → build-up in food chains → organisms harmed