Biological consequences of smoking

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 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").

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).

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.

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.

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".

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.