Pollution ICSE Class 10: Sources, Effects and Control Measures

What Pollution is about

Weightage: CISCE publishes no chapter or unit weightage for ICSE Biology. Pollution is in the 6. Pollution part of the 2027 syllabus and can be asked in both Section A and Section B of the 80-mark paper.Source: CISCE ICSE Biology (Science Paper 3) syllabus, examination year 2027

Key concepts

Air pollution

Source	Main pollutants
Vehicles	carbon monoxide (CO), nitrogen oxides, unburnt hydrocarbons, particulate matter (soot), lead (from leaded petrol)
Industries	sulphur dioxide, nitrogen oxides, smoke, fly ash
Burning garbage	smoke, soot, toxic gases from burning plastics
Brick kilns	smoke, soot, CO, SO₂

Effects: breathing problems (asthma, bronchitis), eye irritation, smog, acid rain, global warming.

Carbon monoxide is especially dangerous: it combines with haemoglobin far more readily than oxygen does, forming a stable compound, carboxyhaemoglobin. This reduces the oxygen-carrying capacity of blood, causing headache, dizziness, unconsciousness and, in large amounts, death.

Worked example

How does breathing in a lot of carbon monoxide cut the oxygen supply to the body's tissues?

Try it first, then show the solutionSolution

1. CO combines with haemoglobin to form carboxyhaemoglobin, a stable compound.
2. That haemoglobin can no longer carry oxygen.
3. Tissues are starved of oxygen; it may cause suffocation and death.

Answer: It forms carboxyhaemoglobin, reducing oxygen transport.

Water and thermal pollution

Water pollution sources:

• Household detergents: contain phosphates, which (like fertiliser run-off) make algae grow rapidly (algal bloom, eutrophication). When the algae die and decay, bacteria use up the dissolved oxygen, and fish die.
• Sewage: carries disease-causing germs (cholera, typhoid, jaundice) and organic matter that uses up oxygen as it decays.
• Industrial waste: toxic chemicals and heavy metals such as mercury and lead, which poison aquatic life and enter food chains.
• Oil spills (from ships and tankers): oil spreads as a film on the sea, coats the feathers of birds and the gills of fish, and blocks oxygen and light.

Thermal pollution: hot water released by power plants (including nuclear plants) and industries that use water for cooling raises the temperature of rivers and lakes. Warm water holds less dissolved oxygen, so fish and other aquatic animals suffer and may die.

Worked example

A nuclear power plant releases its cooling water, still warm, into a river. Name the type of pollution and one effect.

Try it first, then show the solutionSolution

1. The pollutant here is heat: thermal pollution.
2. Warm water holds less dissolved oxygen, harming fish.

Answer: Thermal pollution; less oxygen for aquatic animals.

Soil, biomedical, radiation and noise pollution

Soil pollution: industrial waste (chemicals, heavy metals, fly ash); urban commercial and domestic waste (plastic bags, metal cans, glass); chemical fertilisers used in excess, which change the soil's pH, harm useful soil organisms and wash into water bodies; pesticides.

Biomedical waste: waste produced in hospitals, clinics and laboratories during diagnosis and treatment: used needles and syringes, soiled dressings and cotton, blood, body parts, discarded medicines. If not disposed of safely (segregated, then incinerated or sterilised), it can spread infections such as hepatitis B.

Radiation pollution: from X-rays (overuse) and radioactive fallout from nuclear plants (leaks, accidents) and nuclear tests. It can cause mutations, cancers such as leukaemia, and burns.

Noise pollution: unwanted loud sound from motor vehicles, industries, construction sites and loudspeakers. Effects: hearing loss, disturbed sleep, stress, irritability, headache and high blood pressure.

Worked example

A clinic produces several kinds of rubbish. Which of it counts as biomedical waste? Define the term and name two such items.

Try it first, then show the solutionSolution

1. Wastes generated by hospitals, clinics and laboratories in diagnosis and treatment.
2. Examples: used syringes and needles; soiled dressings.

Answer: As above.

Biodegradable and non-biodegradable wastes

• Biodegradable wastes can be broken down by microorganisms (bacteria, fungi) into harmless substances: paper, vegetable and fruit peels, leaves, wood, cotton cloth, animal dung.
• Non-biodegradable wastes cannot be broken down by microorganisms and stay in the environment for a very long time: plastics, glass, Styrofoam, metal cans, and pesticides such as DDT.

DDT is a persistent pesticide: it does not break down, so it collects in the fatty tissues of organisms and its concentration increases at each level of a food chain (biomagnification), harming top predators such as fish-eating birds.

Worked example

Classify: Styrofoam cup, banana peel, newspaper, glass bottle, DDT.

Try it first, then show the solutionSolution

1. Microbes can decompose banana peel and newspaper: biodegradable.
2. Styrofoam, glass and DDT are not decomposed: non-biodegradable.

Answer: Biodegradable: banana peel, newspaper. Non-biodegradable: Styrofoam, glass, DDT.

Greenhouse effect, acid rain and ozone depletion

Greenhouse effect and global warming: gases such as carbon dioxide, methane, nitrous oxide and CFCs let sunlight through but trap the heat radiated back by the earth, like the glass of a greenhouse. More of these gases (from burning fuels, deforestation, paddy fields, cattle) means more heat is trapped, so the earth's average temperature rises: global warming. Effects: melting glaciers and polar ice, rise in sea level, changes in rainfall, floods and droughts.

Acid rain: sulphur dioxide and nitrogen oxides from fuels dissolve in rainwater to form sulphuric and nitric acids. Effects: corrosion of buildings and marble monuments, damage to leaves and forests, acidification of lakes (fish die), and leaching of nutrients from the soil.

Ozone layer depletion: the ozone layer in the upper atmosphere absorbs harmful ultraviolet (UV) rays. Chlorofluorocarbons (CFCs), used in refrigerators, air conditioners and aerosol sprays, release chlorine that breaks down ozone. More UV reaching the earth causes skin cancer, cataract, weaker immunity and crop damage.

Worked example

How does acid rain harm (a) marble buildings and (b) lakes?

Try it first, then show the solutionSolution

1. It corrodes buildings and marble monuments.
2. It acidifies lakes, killing fish (also damages leaves and leaches soil nutrients).

Answer: Corrosion of monuments; death of aquatic life (or soil nutrient loss).

Control measures and Swachh Bharat Abhiyan

• Unleaded petrol / CNG (compressed natural gas) in vehicles: no lead emissions; CNG burns cleaner, with far less smoke.
• Switching off engines at traffic signals: less fuel burnt, fewer exhaust gases.
• Social forestry: planting trees on public and common land (roadsides, canal banks); trees absorb CO₂ and dust and reduce noise.
• Sewage treatment plants: treat sewage before it is released into rivers.
• Ban on polythene and plastics: less non-biodegradable waste.
• Organic farming: manure and natural pest control instead of chemical fertilisers and pesticides.
• Euro / Bharat Stage (BS) vehicular standards: legal limits on vehicle emissions.

Swachh Bharat Abhiyan is a national campaign for a Clean India. Its objectives include ending open defecation by building toilets, proper collection and disposal of solid waste, keeping streets and public places clean, and creating awareness about sanitation and hygiene.

Worked example

What does Swachh Bharat Abhiyan set out to achieve? Give two of its aims.

Try it first, then show the solutionSolution

1. To eliminate open defecation by building toilets.
2. To manage solid waste scientifically and keep public places clean (also awareness of sanitation).

Answer: As above.

Pollution in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Types and Sources of Pollution
• Greenhouse Effect, Acid Rain and Ozone Depletion

Pollution: key facts

Acid rain formation (simplified)

$S{O}_2+H_{2}O\to H_{2}S{O}_3;2S{O}_2+O_2+2H_{2}O\to 2H_{2}S{O}_4$

Nitrogen oxides similarly form nitric acid.

Carboxyhaemoglobin

$Hb+CO\to HbCO$

Stable; blocks oxygen transport.

Combustion of fuels

$C{H}_4+2O_2\to C{O}_2+2H_{2}O$

CO₂ is a greenhouse gas.

Expansions

$\text{CFC = chlorofluorocarbon};\text{CNG = compressed natural gas};\text{BS = Bharat Stage}$

Common abbreviations.

Pollution: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Pollution

The question patterns to expect, and the method that works for each.

Tricks to remember Pollution

Short memory aids. Say each one aloud once, then use it on a question the same day.

• CO grabs Hb

  Carbon monoxide grabs haemoglobin tighter than oxygen: HbCO.

  Use it when: Why CO is dangerous.

• SO-NO make acid rain

  SO₂ and NO₂ in rain make sulphuric and nitric acids.

  Use it when: Acid rain causes.

• CFCs Chew the ozone

  Chlorine from CFCs chews holes in the ozone layer.

  Use it when: Ozone depletion.

• Hot water holds less O₂

  Like a warm fizzy drink losing gas, warm water loses oxygen.

  Use it when: Thermal pollution.

Pollution: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 6-mark question split into 1 + 2 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Pollution

The slips examiners see most often, and what to write instead.

• ✗Mistake: Water or radiation pollution for thermal

  CISCE examiners' comments, 2025: for warm cooling water from nuclear plants, candidates chose radiation or water pollution.

  Wrong working

  Radiation pollution.

  Right working

  Thermal pollution (heat is the pollutant).

  ✓Do this: Ask: what is the harmful agent? Heat = thermal.

  Usually costs: 1 mark.

• ✗Mistake: Wrong compound for CO

  CISCE examiners' comments, 2024: candidates gave vague answers or wrote carbamino haemoglobin instead of carboxyhaemoglobin.

  Wrong working

  CO forms carbaminohaemoglobin.

  Right working

  CO forms carboxyhaemoglobin, which reduces oxygen transport.

  ✓Do this: Carboxy- for CO; carbamino- is CO₂ transport.

  Usually costs: 1 mark.

• ✗Mistake: Vague effects of acid rain and noise

  CISCE examiners' comments, 2025: candidates wrote 'pollution', 'harms plants' or 'it is noisy' instead of specific effects such as corrosion of monuments, leaching of nutrients, sleep disturbance or hearing loss.

  Wrong working

  Acid rain harms plants.

  Right working

  Acid rain corrodes marble monuments and leaches nutrients from soil.

  ✓Do this: Give a named, specific effect.

  Usually costs: 1 mark each.

• ✗Mistake: Measures given as objectives

  CISCE examiners' comments, 2024 and 2025: for objectives of Swachh Bharat Abhiyan, candidates listed air pollution control measures or vague aims like 'to keep clean'.

  Wrong working

  Use CNG vehicles.

  Right working

  End open defecation; manage solid waste; clean public places.

  ✓Do this: Link objectives to sanitation and waste.

  Usually costs: 1 mark each.

• ✗Mistake: Biomedical vs biodegradable

  CISCE examiners' comments, 2025: candidates wrote 'waste from medicals', gave 'plastic' as an example, or confused biomedical with biodegradable waste.

  Wrong working

  Biomedical waste: waste that decomposes.

  Right working

  Waste from hospitals, clinics and laboratories, e.g. used syringes.

  ✓Do this: Biomedical = from health care.

  Usually costs: 1 mark.

• ✗Mistake: Wrong expansions

  CISCE examiners' comments, 2025: candidates expanded CFC as 'compressed fluorocarbons' and confused CNG with LPG or invented terms.

  Wrong working

  CNG = carbon neutral gas.

  Right working

  CNG = compressed natural gas; CFC = chlorofluorocarbon.

  ✓Do this: Learn the expansions exactly.

  Usually costs: 1 mark each.

Practice questions on Pollution

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which of the following is non-biodegradable?
   (a) Vegetable peel
   (b) Paper
   (c) Styrofoam
   (d) Cotton cloth

   Hint

   Microbes can't break it.

   Answer

   (c)

2. Q2 · 1 mark · MCQBoard level

   Acid rain is mainly caused by:
   (a) CO₂ and CH₄
   (b) SO₂ and NO₂
   (c) CFCs
   (d) O₃

   Hint

   SO-NO.

   Answer

   (b)

3. Q3 · 1 mark · Very short answerHarder board level

   Odd one out, with category: used syringe, soiled dressing, banana peel, discarded needle.

   Hint

   Hospital waste.

   Answer

   Banana peel; the others are biomedical wastes.

4. Q4 · 1 mark · Assertion-reasonHarder board level

   Assertion (A): Organic farming reduces soil pollution.
   Reason (R): Organic farming uses chemical fertilisers in larger amounts.
   (a) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (b) Both (A) and (R) are true, but (R) is not the correct explanation for (A).
   (c) (A) is true and (R) is false.
   (d) (A) is false and (R) is true.

   Hint

   Manure, not chemicals.

   Answer

   (c)

5. Q5 · 2 marks · Short answerHarder board level

   A school stands next to a construction site where drilling goes on all day. Give two harmful effects of this noise on the students.

   Hint

   Ears and sleep.

   Answer

   Hearing loss; disturbed sleep (also stress, high blood pressure, headache).

6. Q6 · 2 marks · Short answerHarder board level

   Name the sources of radiation pollution mentioned in the syllabus and give two of its effects.

   Hint

   Medical and nuclear.

   Answer

   X-rays and radioactive fallout from nuclear plants. Effects: mutations (genetic defects), cancers such as leukaemia (also burns).

7. Q7 · 3 marks · Short answerHarder board level

   How do household detergents cause the death of fish in ponds?

   Hint

   Phosphates and algae.

   Answer

   Phosphates in detergents act as nutrients, causing an algal bloom. Dead algae are decomposed by bacteria, which use up dissolved oxygen, so fish die.

8. Q8 · 2 marks · Short answerHarder board level

   Explain how switching off engines at traffic signals and Bharat Stage norms reduce air pollution.

   Hint

   Less fuel; limits.

   Answer

   Switching off engines stops fuel burning while idle, cutting exhaust gases. Bharat Stage norms set legal limits on vehicle emissions, forcing cleaner engines and fuels.

9. Q9 · 3 marks · Case-basedHOTS / competency

   A city replaces diesel buses with CNG buses and plants trees along roads. Predict two changes in air quality and one health benefit.

   Hint

   Smoke, dust, CO₂.

   Answer

   Less smoke, soot and unburnt hydrocarbons from buses; trees absorb dust and CO₂ and reduce noise. Health benefit: fewer breathing problems such as asthma and bronchitis.

10. Q10 · 2 marks · Short answerHOTS / competency

    Why does a ban on polythene bags help both soil and water, even though polythene is not poisonous to touch?

    Hint

    Non-biodegradable effects.

    Answer

    Polythene is non-biodegradable: it stays in soil, blocking water and air movement and harming soil fertility, and it clogs drains and water bodies; animals that swallow it can die.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Gas from vehicles that forms carboxyhaemoglobin?Show answer

   Carbon monoxide.

2. 2.Two gases causing acid rain?Show answer

   Sulphur dioxide and nitrogen oxides.

3. 3.Chemicals responsible for ozone depletion?Show answer

   Chlorofluorocarbons (CFCs).

4. 4.Two examples of non-biodegradable waste?Show answer

   Plastics and glass (also Styrofoam, DDT).

5. 5.Two examples of biomedical waste?Show answer

   Used syringes and soiled dressings.

6. 6.Effect of thermal pollution?Show answer

   Less dissolved oxygen in water; aquatic animals die.

7. 7.Expand CNG.Show answer

   Compressed natural gas.

8. 8.Purpose of social forestry?Show answer

   Planting trees on public land to absorb pollutants, provide fuel and fodder, and green the area.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you list sources of air, water, soil, biomedical, radiation and noise pollution?
• ☐Can you explain why CO is dangerous?
• ☐Can you give two specific effects of acid rain, noise and ozone depletion?
• ☐Can you classify any waste as biodegradable or not?
• ☐Can you explain how CNG, social forestry and sewage treatment help?
• ☐Can you write two objectives of Swachh Bharat Abhiyan?

Pollution: frequently asked questions