Why is "Mixing up the effects of tar, nicotine and carbon monoxide" a common mistake in Biological consequences of smoking?

Why it happens: Students learn 'smoking is harmful' as one blurred idea instead of three separate chemicals with distinct effects. How to avoid it: Pair each chemical with its own effect: tar = carcinogen + cilia damage; nicotine = addictive + heart rate/blood pressure; carbon monoxide = binds haemoglobin → less oxygen. Source: Edexcel Biology examiner reports

Why is "Saying carbon monoxide damages the lungs or stops you breathing" a common mistake in Biological consequences of smoking?

Why it happens: Smoke is breathed into the lungs, so students assume every chemical acts there. How to avoid it: Carbon monoxide acts in the **blood** — it **binds to haemoglobin** and reduces **oxygen transport**. It is a circulatory effect, not a direct lung-damage effect. Source: Edexcel Biology examiner reports 2023–2024

Why is "Writing 'tar damages the lungs' without a mechanism" a common mistake in Biological consequences of smoking?

Why it happens: It feels like a complete answer, but it states the outcome without explaining how. How to avoid it: Give the mechanism: tar is a **carcinogen** (→ lung cancer) **and** it **destroys cilia** so mucus builds up (→ bronchitis). Source: Edexcel Biology examiner reports

Why is "Describing emphysema without mentioning surface area" a common mistake in Biological consequences of smoking?

Why it happens: Students say 'alveoli are damaged' but forget to link this to gas exchange. How to avoid it: Always state that damaged alveoli mean a **reduced surface area for gas exchange**, so **less oxygen** diffuses into the blood — that link is the marked point. Source: Edexcel Biology examiner reports

Why is "Confusing carbon monoxide (CO) with carbon dioxide (CO₂)" a common mistake in Biological consequences of smoking?

Why it happens: The names look similar and both are gases linked to the lungs. How to avoid it: Carbon **monoxide** is the harmful gas in smoke that binds haemoglobin. Carbon **dioxide** is the normal waste gas of respiration — do not swap them. Source: Edexcel Biology examiner reports

Why is "Claiming nicotine causes cancer" a common mistake in Biological consequences of smoking?

Why it happens: Nicotine is the best-known smoking chemical, so students assume it does the most damage. How to avoid it: **Tar** is the carcinogen that causes cancer. **Nicotine** is **addictive** and affects the heart rate and blood pressure — it is not the cancer-causing chemical. Source: Edexcel Biology examiner reports

Edexcel IGCSE Science(Double Award)-Biology (4WSD0-1B)

Biological consequences of smoking

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Detailed Study Notes

Detailed notes on Gas Exchange Function of Living Organisms for Edexcel IGCSE Science(Double Award)-Biology, covering key concepts, explanations, examples, and exam-focused revision points.

Biological Consequences of Smoking — Edexcel International GCSE Science (Double Award) Biology (4WSD0-1B) Study Notes

How the chemicals in tobacco smoke — tar, nicotine and carbon monoxide — harm the lungs and the circulatory system, causing lung cancer, bronchitis, emphysema and coronary heart disease. Covers Double Award Biology spec 2.49, assessed on Biology Paper 1 (4WSD0/1B).

At a glance

Three named chemicals to learn: tar, nicotine and carbon monoxide.
Tar is a carcinogen → causes lung cancer; it also damages the cilia, leading to bronchitis.
Nicotine is addictive and raises heart rate and blood pressure.
Carbon monoxide binds to haemoglobin in red blood cells, reducing oxygen transport.
Emphysema = alveoli walls damaged/broken down → reduced surface area for gas exchange → breathlessness.
Coronary heart disease (CHD) = damage to the heart's blood supply, made more likely by smoking.
Effects split neatly into lungs (tar, cilia, emphysema) and circulatory system (nicotine, CO, CHD).

What you’ll learn

Mapped to the Edexcel IGCSE 4SD0 syllabus (2026 onwards).

2.49 — Understand the biological consequences of smoking in relation to the lungs and the circulatory system, including the effect of tar, nicotine and carbon monoxide.

The three chemicals in tobacco smoke (spec 2.49)

Tar, nicotine and carbon monoxide each cause different harm.

Tobacco smoke contains thousands of substances, but for Paper 1 (4WSD0/1B) you must know three named chemicals and exactly what each one does:

Tar — a sticky brown substance that is a carcinogen (a chemical that causes cancer). It also damages the cilia lining the airways.
Nicotine — the addictive drug in tobacco. It increases heart rate and raises blood pressure.
Carbon monoxide — a poisonous gas that binds to haemoglobin in red blood cells, reducing the oxygen they can carry.

A clean way to organise your answer is by where the harm happens:

Chemical	Main effect	System affected
Tar	Carcinogen → lung cancer; damages cilia → bronchitis	Lungs
Nicotine	Addictive; raises heart rate + blood pressure	Circulatory system
Carbon monoxide	Binds haemoglobin → less oxygen carried	Circulatory system

Exam tip. When a question says "name a chemical in tobacco smoke and describe its effect", pick one chemical and give its specific effect — don't blur tar, nicotine and CO together.

Tar = carcinogen + cilia damage.
Nicotine = addictive + raises heart rate/blood pressure.
Carbon monoxide = binds haemoglobin, reduces oxygen transport.

See the full worked example for biological consequences of smoking →

Tar, cilia and the lungs (lung cancer & bronchitis)

Tar is a carcinogen and it stops the airways being cleaned.

Tar causes lung cancer. Tar is a carcinogen — it damages the DNA in lung cells, causing them to divide uncontrollably and form a tumour (cancer).

Tar causes bronchitis by damaging cilia. Normally the airways are lined with:

goblet cells that make mucus to trap dust and microbes, and
cilia — tiny hair-like structures that beat to sweep the mucus up out of the lungs.

Tar paralyses and destroys the cilia, so mucus can no longer be swept away. Mucus then builds up in the airways, which become infected and inflamed — this is bronchitis. The person coughs to try to clear the trapped mucus ("smoker's cough").

Tar destroys the cilia, so mucus is no longer swept out — it collects in the airways, causing bronchitis.

Exam tip. Many marks are lost because students write "tar damages the lungs". State the mechanism: tar is a carcinogen (cancer) and it destroys cilia so mucus builds up (bronchitis).

Tar is a carcinogen → lung cancer.
Cilia normally sweep mucus out of the airways.
Tar destroys cilia → mucus builds up → bronchitis.

See the full worked example for biological consequences of smoking →

Emphysema — alveoli damaged, surface area lost

Broken alveoli walls mean far less surface for gas exchange.

Emphysema is a long-term lung disease linked to smoking. Repeated coughing and inflammation damage and break down the walls of the alveoli (the tiny air sacs where gas exchange happens).

Many small alveoli merge into fewer, larger air spaces.
This greatly reduces the surface area available for gas exchange.
Less oxygen can diffuse into the blood, so the person becomes breathless, even with gentle activity.

Link it back to gas exchange. Healthy alveoli give a large surface area for efficient diffusion of oxygen and carbon dioxide. Emphysema destroys that large surface area, so the lungs work far less efficiently.

Exam tip. The key marking phrase is "reduced surface area for gas exchange", leading to reduced oxygen uptake / breathlessness.

Emphysema = alveoli walls damaged/broken down.
Surface area for gas exchange is reduced.
Result: less oxygen absorbed → breathlessness.

See the full worked example for biological consequences of smoking →

Nicotine, carbon monoxide and the circulatory system

Nicotine speeds the heart; CO starves the blood of oxygen.

Smoking also harms the heart and blood vessels (the circulatory system).

Nicotine is addictive (which is why smoking is hard to quit) and it acts as a stimulant:

it increases the heart rate, and
it raises blood pressure (partly by narrowing blood vessels).

Both of these put extra strain on the heart and arteries.

Carbon monoxide is a poisonous gas that reduces how much oxygen the blood can carry:

it binds to haemoglobin in red blood cells (more strongly than oxygen does), and
this means less oxygen can be picked up and transported around the body.

So the heart has to work even harder to deliver enough oxygen — while CO is at the same time reducing the oxygen available. This combination contributes to coronary heart disease (CHD): the coronary arteries that supply the heart muscle become damaged/blocked, the heart muscle is starved of oxygen, and this can lead to chest pain or a heart attack.

Carbon monoxide binds to haemoglobin instead of oxygen, so the blood carries less oxygen around the body.

Exam tip. For CO, the marking points are "binds to haemoglobin" and "reduces oxygen transport/carriage". For nicotine, it's "addictive" and "increases heart rate and blood pressure".

Nicotine: addictive; raises heart rate and blood pressure.
Carbon monoxide: binds haemoglobin → less oxygen carried.
Together they increase the risk of coronary heart disease.

See the full worked example for biological consequences of smoking →

Putting it together — lungs vs circulation

Sort each effect under 'lungs' or 'circulatory system'.

The whole of spec 2.49 fits onto one map. Decide whether each effect is on the lungs or the circulatory system:

Effects on the LUNGS

Tar → carcinogen → lung cancer.
Tar → destroys cilia → mucus builds up → bronchitis.
Emphysema → alveoli damaged → reduced surface area → breathlessness.

Effects on the CIRCULATORY SYSTEM

Nicotine → addictive; raises heart rate and blood pressure.
Carbon monoxide → binds haemoglobin → less oxygen carried.
These contribute to coronary heart disease (CHD).

How to revise this. Make a two-column table (Lungs | Circulation) and write each chemical/disease into the correct column with its one-line mechanism. If a question asks specifically about "the circulatory system", do not waste time writing about cilia or alveoli — keep to nicotine, CO and CHD.

Lungs: tar (cancer + bronchitis), emphysema (alveoli/surface area).
Circulation: nicotine (heart rate/BP), CO (haemoglobin/oxygen), CHD.
Match your answer to the system the question asks about.

See the full worked example for biological consequences of smoking →

Quick recap

Three chemicals: tar, nicotine and carbon monoxide — each with a specific effect.
Tar is a carcinogen (lung cancer) and destroys cilia (mucus builds up → bronchitis).
Emphysema damages alveoli, reducing surface area for gas exchange → breathlessness.
Nicotine is addictive and raises heart rate and blood pressure.
Carbon monoxide binds haemoglobin, reducing oxygen transport; smoking raises CHD risk.

Memorise this

Verbatim phrases and definitions Edexcel mark schemes credit.

Tar = carcinogen (lung cancer) + damages cilia → mucus builds up → bronchitis.
Nicotine = addictive + raises heart rate and blood pressure.
Carbon monoxide = binds haemoglobin → reduces oxygen transport.
Emphysema = alveoli walls damaged → reduced surface area for gas exchange.
Coronary heart disease (CHD) = damaged blood supply to heart muscle; smoking increases the risk.
Cilia = hair-like structures that sweep mucus up out of the airways.
Sort effects into lungs (tar, cilia, emphysema) and circulation (nicotine, CO, CHD).

How it’s examined

Assessed on Biology Paper 1 (4WSD0/1B), 2 hours, 110 marks, untiered. Common question shapes: 'name a chemical in tobacco smoke and describe its effect' (2–3 marks), 'explain how tar leads to bronchitis' (cilia → mucus), 'explain how carbon monoxide reduces oxygen delivery' (binds haemoglobin), and 'explain how emphysema affects gas exchange' (reduced surface area). The keyword credits — carcinogen, cilia, haemoglobin, surface area — are reliable marks.

Sources: Pearson Edexcel International GCSE Science (Double Award) 4SD0 specification — Issue 4, September 2024 (valid for 2026 onwards); Pearson Edexcel International GCSE Biology 4BI1 specification — Issue 4 (shared Biology Paper 1 content); Pearson Edexcel 4SD0 / 4BI1 examiner reports 2022–2024. Last reviewed 2026-06-04.

Take this whole topic with you

Step-by-step worked examples — Biological consequences of smoking

Step-by-step solutions to past-paper-style questions on biological consequences of smoking, written exactly the way a tutor would explain them at the board.

Question type:

1Name a chemical in tobacco smoke and its effect (Getting started)
Getting startedIdentify & classify• 4WSD0/1B style — short answer• nicotine, spec-2.49
Question
Tobacco smoke contains nicotine. State two effects of nicotine on the body. (2 marks)
Step-by-step solution
1. Step 1
  Effect 1 (1). Nicotine is addictive — it makes the smoker dependent on tobacco.
2. Step 2
  Effect 2 (1). Nicotine increases heart rate and raises blood pressure.
Answer
Nicotine is addictive; it increases heart rate and raises blood pressure.
Examiner tip
Don't confuse nicotine's effects with those of tar or carbon monoxide. 'Addictive' + 'raises heart rate/blood pressure' are the two safe marking points.
2Why smokers get a 'smoker's cough' (Getting started)
Getting startedIdentify & classify• 4WSD0/1B style — short answer• tar, cilia, bronchitis, spec-2.49
Question
Tar in tobacco smoke damages structures in the airways. Name these structures and state what they normally do. (2 marks)
Step-by-step solution
1. Step 1
  Structure (1). The cilia (tiny hair-like structures lining the airways).
2. Step 2
  Normal job (1). They beat to sweep mucus (and trapped dust/microbes) up and out of the lungs.
Answer
Cilia — they normally sweep mucus and trapped particles up out of the airways.
Examiner tip
Once tar destroys the cilia, mucus is no longer cleared, so it builds up — leading to coughing and bronchitis.
3How carbon monoxide reduces oxygen transport (Building confidence)
Building confidenceMulti-step problem• 4WSD0/1B style — structured• carbon-monoxide, haemoglobin, spec-2.49
Question
Explain how carbon monoxide in tobacco smoke reduces the amount of oxygen carried around the body. (3 marks)
Step-by-step solution
1. Step 1
  Where it acts (1). Carbon monoxide enters the blood and binds to haemoglobin in red blood cells.
2. Step 2
  Why this matters (1). It binds in place of oxygen (and more strongly than oxygen), so less haemoglobin is free to carry oxygen.
3. Step 3
  Consequence (1). Therefore less oxygen is transported to the body's cells/tissues.
Answer
Carbon monoxide binds to haemoglobin in red blood cells (in place of oxygen), so the blood carries less oxygen around the body.
Examiner tip
The two essential marking words are 'haemoglobin' and 'less oxygen carried/transported'. Saying CO 'fills the lungs' scores nothing.
4Explain breathlessness in emphysema (Building confidence)
Building confidenceMulti-step problem• 4WSD0/1B style — structured• emphysema, alveoli, gas-exchange, spec-2.49
Question
A heavy smoker develops emphysema and becomes breathless. Explain why, referring to the alveoli. (3 marks)
Step-by-step solution
1. Step 1
  Damage (1). Emphysema damages and breaks down the walls of the alveoli.
2. Step 2
  Effect on structure (1). This reduces the surface area available for gas exchange.
3. Step 3
  Effect on the body (1). Less oxygen can diffuse into the blood, so the person cannot get enough oxygen and becomes breathless.
Answer
Emphysema breaks down the alveoli walls, reducing the surface area for gas exchange, so less oxygen diffuses into the blood — the person becomes breathless.
Examiner tip
'Reduced surface area for gas exchange' is the pivotal mark. Link it to reduced oxygen uptake / breathlessness for full credit.
5Two separate effects of tar on the lungs (Stretch)
StretchMulti-step problem• 4WSD0/1B style — extended• tar, lung-cancer, bronchitis, spec-2.49
Question
Tar is one chemical found in tobacco smoke. Explain two different ways in which tar can damage the lungs. (4 marks)
Step-by-step solution
1. Step 1
  Cancer route (1). Tar is a carcinogen — a chemical that causes cancer.
2. Step 2
  Cancer outcome (1). It damages lung cells so they divide uncontrollably, forming a tumour — this is lung cancer.
3. Step 3
  Bronchitis route (1). Tar destroys the cilia that normally sweep mucus out of the airways.
4. Step 4
  Bronchitis outcome (1). Mucus then builds up, the airways become infected/inflamed — this is bronchitis.
Answer
(1) Tar is a carcinogen, damaging lung cells so they divide uncontrollably → lung cancer. (2) Tar destroys the cilia, so mucus is no longer swept out and builds up → bronchitis.
Examiner tip
Two distinct mechanisms are required. A common error is giving only one effect twice; keep cancer (carcinogen) and bronchitis (cilia/mucus) clearly separate.
6Sort smoking effects: lungs vs circulation (Stretch)
StretchIdentify & classify• 4WSD0/1B style — extended• tar, nicotine, carbon-monoxide, spec-2.49
Question
For each of tar, nicotine and carbon monoxide, name one harmful effect and state whether it mainly affects the lungs or the circulatory system. (6 marks)
Step-by-step solution
1. Step 1
  Tar — effect (1). Carcinogen → lung cancer (or: destroys cilia → bronchitis).
2. Step 2
  Tar — system (1). Affects the lungs.
3. Step 3
  Nicotine — effect (1). Addictive; raises heart rate and blood pressure.
4. Step 4
  Nicotine — system (1). Affects the circulatory system.
5. Step 5
  Carbon monoxide — effect (1). Binds to haemoglobin, reducing oxygen transport.
6. Step 6
  Carbon monoxide — system (1). Affects the circulatory system.
Answer
Tar → lung cancer / bronchitis (lungs). Nicotine → addictive, raises heart rate and blood pressure (circulatory system). Carbon monoxide → binds haemoglobin, reduces oxygen transport (circulatory system).
Examiner tip
1 mark for each correct effect + 1 for the correct system. Examiners reward answers that match the named chemical to the right body system rather than blurring them together.

Model Answers — Biological consequences of smoking

High-scoring sample answers for biological consequences of smoking on the Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
4WSD0/1B style2 marks
Name one chemical found in tobacco smoke and describe one harmful effect it has on the body. (2 marks)
Model answer
Carbon monoxide (1).

It binds to the haemoglobin in red blood cells, so the blood carries less oxygen around the body (1).

(Equally acceptable: tar — a carcinogen that causes lung cancer / destroys cilia; nicotine — addictive and raises heart rate and blood pressure.)
Why this scores
1 mark for a correctly named chemical, 1 for its specific effect. Vague effects like 'it is bad for you' score nothing.
Question 2
4WSD0/1B style3 marks
Explain how tar in tobacco smoke leads to a build-up of mucus in a smoker's airways. (3 marks)
Model answer
The airways are lined with cilia, tiny hair-like structures that normally sweep mucus up and out of the lungs (1).

Tar destroys / paralyses the cilia (1).

Without working cilia the mucus is no longer cleared, so it builds up in the airways (and can lead to bronchitis) (1).
Why this scores
The mark scheme wants the normal role of cilia, the damage by tar, and the consequence (mucus build-up). Naming 'cilia' is essential.
Question 3
4WSD0/1B style5 marks
Describe what happens to the lungs in emphysema and explain how this affects gas exchange. (5 marks)
Model answer
Long-term smoking causes inflammation and repeated coughing that damage the walls of the alveoli (1).

The alveoli walls break down, so many small alveoli merge into fewer, larger air spaces (1).

This reduces the total surface area available for gas exchange (1).

Less oxygen can diffuse into the blood (and less carbon dioxide is removed) (1).

The person gets too little oxygen and becomes breathless, even with gentle activity (1).
Why this scores
Up to 5 marks following the chain: alveoli damaged → walls break down → reduced surface area → reduced diffusion of oxygen → breathlessness. 'Reduced surface area' is the key linking idea.
Question 4
4WSD0/1B style6 marks
Smoking affects the circulatory system. Explain how nicotine and carbon monoxide each affect the body. (6 marks)
Model answer
Nicotine

Is addictive, which makes it hard for a smoker to stop (1).

Increases the heart rate (1).

Raises blood pressure (partly by narrowing blood vessels), putting extra strain on the heart and arteries (1).

Carbon monoxide

Is a poisonous gas that binds to the haemoglobin in red blood cells (1).

It binds in place of oxygen, so the blood carries less oxygen (1).

The heart must work harder to deliver enough oxygen to the body's tissues (1).
Why this scores
Up to 3 marks per chemical. Keep nicotine (addictive / heart rate / blood pressure) and carbon monoxide (haemoglobin / less oxygen) clearly separated — mixing them loses marks.
Question 5
4WSD0/1B style — extended open response7 marks
Explain how the chemicals in tobacco smoke increase a smoker's risk of coronary heart disease. (7 marks)
Model answer
Coronary heart disease (CHD) occurs when the coronary arteries that supply the heart muscle with oxygenated blood become damaged or blocked, starving the heart muscle of oxygen.

Nicotine is a stimulant that increases the heart rate and raises blood pressure (1).

Higher heart rate and blood pressure put the heart and arteries under greater strain (1).

Raised blood pressure can damage the lining of the coronary arteries (1).

Carbon monoxide binds to haemoglobin in red blood cells (1).

This means the blood carries less oxygen, so the heart muscle receives less oxygen (1).

With the arteries damaged/narrowed and the blood carrying less oxygen, the heart muscle can become starved of oxygen (1).

This raises the risk of chest pain and a heart attack — i.e. coronary heart disease (1).
Why this scores
Examiners reward a linked chain: nicotine (heart rate/blood pressure/strain) + carbon monoxide (haemoglobin → less oxygen) → heart muscle short of oxygen → CHD. Marks come from the mechanism, not just naming the chemicals.
Question 6
4WSD0/1B style — extended open response9 marks
Give a full account of the biological consequences of smoking on both the lungs and the circulatory system, naming the chemicals responsible. (9 marks)
Model answer
Effects on the lungs

Tar is a carcinogen: it damages lung cells so they divide uncontrollably, forming a tumour — lung cancer (1).

Tar also destroys the cilia that line the airways (1).

Cilia normally sweep mucus out, so without them mucus builds up and the airways become infected/inflamed — bronchitis (1).

Long-term damage breaks down the alveoli walls, reducing the surface area for gas exchange — emphysema — causing breathlessness (1).

Effects on the circulatory system

Nicotine is addictive (1).

Nicotine increases heart rate and raises blood pressure, straining the heart and arteries (1).

Carbon monoxide binds to haemoglobin in red blood cells (1).

This reduces the oxygen the blood can transport around the body (1).

Together these effects increase the risk of coronary heart disease, where the heart muscle is starved of oxygen (1).
Why this scores
Up to ~4–5 marks per system. Strong answers name the chemical AND its mechanism (carcinogen, cilia, alveoli/surface area, haemoglobin, heart rate/blood pressure) and place each effect under the correct body system.

Key Definitions and Keywords — Biological consequences of smoking

Definitions to memorise and the exact keywords mark schemes credit for biological consequences of smoking answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) sitting.

Tar
Examiner keyword
A sticky brown substance in tobacco smoke that is a carcinogen (causes lung cancer) and damages the cilia lining the airways.
Nicotine
Examiner keyword
The addictive drug in tobacco smoke; it acts as a stimulant, increasing heart rate and raising blood pressure.
Carbon monoxide
Examiner keyword
A poisonous gas in tobacco smoke that binds to haemoglobin in red blood cells, reducing the amount of oxygen the blood can carry.
Carcinogen
Examiner keyword
A chemical that can cause cancer by damaging cells so that they divide uncontrollably. Tar is a carcinogen.
Cilia
Examiner keyword
Tiny hair-like structures lining the airways that beat to sweep mucus (and trapped dust/microbes) up and out of the lungs.
Emphysema
Examiner keyword
A lung disease in which the alveoli walls are damaged and break down, reducing the surface area for gas exchange and causing breathlessness.
Bronchitis
Inflammation of the airways caused by a build-up of mucus when tar has destroyed the cilia, leading to coughing and infection.
Coronary heart disease (CHD)
Examiner keyword
Disease in which the coronary arteries supplying the heart muscle become damaged or blocked, starving the heart of oxygen; smoking increases the risk.

Common Mistakes and Misconceptions — Biological consequences of smoking

The traps other students keep falling into on biological consequences of smoking questions — taken from recent Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) examiner reports and mark schemes — and how to avoid them.

✕Mixing up the effects of tar, nicotine and carbon monoxide
Edexcel Biology examiner reports
Why it happens
Students learn 'smoking is harmful' as one blurred idea instead of three separate chemicals with distinct effects.
How to avoid it
Pair each chemical with its own effect: tar = carcinogen + cilia damage; nicotine = addictive + heart rate/blood pressure; carbon monoxide = binds haemoglobin → less oxygen.
✕Saying carbon monoxide damages the lungs or stops you breathing
Edexcel Biology examiner reports 2023–2024
Why it happens
Smoke is breathed into the lungs, so students assume every chemical acts there.
How to avoid it
Carbon monoxide acts in the blood — it binds to haemoglobin and reduces oxygen transport. It is a circulatory effect, not a direct lung-damage effect.
✕Writing 'tar damages the lungs' without a mechanism
Edexcel Biology examiner reports
Why it happens
It feels like a complete answer, but it states the outcome without explaining how.
How to avoid it
Give the mechanism: tar is a carcinogen (→ lung cancer) and it destroys cilia so mucus builds up (→ bronchitis).
✕Describing emphysema without mentioning surface area
Edexcel Biology examiner reports
Why it happens
Students say 'alveoli are damaged' but forget to link this to gas exchange.
How to avoid it
Always state that damaged alveoli mean a reduced surface area for gas exchange, so less oxygen diffuses into the blood — that link is the marked point.
✕Confusing carbon monoxide (CO) with carbon dioxide (CO₂)
Edexcel Biology examiner reports
Why it happens
The names look similar and both are gases linked to the lungs.
How to avoid it
Carbon monoxide is the harmful gas in smoke that binds haemoglobin. Carbon dioxide is the normal waste gas of respiration — do not swap them.
✕Claiming nicotine causes cancer
Edexcel Biology examiner reports
Why it happens
Nicotine is the best-known smoking chemical, so students assume it does the most damage.
How to avoid it
Tar is the carcinogen that causes cancer. Nicotine is addictive and affects the heart rate and blood pressure — it is not the cancer-causing chemical.

Biological consequences of smoking

Detailed Study Notes

At a glance

What you’ll learn

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Name a chemical in tobacco smoke and its effect (Getting started)

2Why smokers get a 'smoker's cough' (Getting started)

3How carbon monoxide reduces oxygen transport (Building confidence)

4Explain breathlessness in emphysema (Building confidence)

5Two separate effects of tar on the lungs (Stretch)

6Sort smoking effects: lungs vs circulation (Stretch)

Tar

Nicotine

Carbon monoxide

Carcinogen

Cilia

Emphysema

Bronchitis

Coronary heart disease (CHD)

✕Mixing up the effects of tar, nicotine and carbon monoxide

✕Saying carbon monoxide damages the lungs or stops you breathing

✕Writing 'tar damages the lungs' without a mechanism

✕Describing emphysema without mentioning surface area

✕Confusing carbon monoxide (CO) with carbon dioxide (CO₂)

✕Claiming nicotine causes cancer