7.3 Smoking and the Risk of Disease

A free GCSE Biology lesson for AQA (8461) from OBA School: nicotine, carbon monoxide and tar; lung disease, cardiovascular disease, cancer and harm in pregnancy. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Name the harmful substances in tobacco smoke and describe their effects
• Explain how smoking increases the risk of lung disease, lung cancer and cardiovascular disease
• Explain how smoking during pregnancy affects the unborn baby
• Interpret data on smoking and disease, including relative risk

Key words

• Nicotine: The addictive drug in tobacco. It raises heart rate and blood pressure.
• Carbon monoxide: A poisonous gas in smoke that combines with haemoglobin, so the blood carries less oxygen.
• Tar: A sticky black mixture that coats the airways and lungs. It contains many carcinogens.
• Cilia: Tiny hairs on cells lining the airways. They sweep mucus, dirt and pathogens up out of the lungs.
• COPD: Chronic obstructive pulmonary disease: long-term lung damage that includes bronchitis and emphysema.
• Relative risk: How many times more likely a group is to get a disease compared with a group without the risk factor.

What is in tobacco smoke?

Tobacco smoke contains thousands of chemicals. Three of the most harmful are nicotine, carbon monoxide and tar.

• Nicotine; Effect on the body addictive, so smokers find it hard to stop; increases heart rate and narrows blood vessels, raising blood pressure
• Carbon monoxide; Effect on the body combines with haemoglobin in red blood cells more readily than oxygen does, so the blood carries less oxygen
• Tar; Effect on the body contains carcinogens; coats the airways and damages the cilia, so mucus builds up in the lungs

Exam tip: Nicotine is the addictive substance, but it is mainly the tar (carcinogens) and carbon monoxide that cause disease.

Lung disease and lung cancer

• Bronchitis: tar damages the cilia, so mucus is not cleared; the airways become inflamed and the smoker develops a "smoker's cough". Infections are more likely.
• Emphysema: the walls of the alveoli break down, forming fewer, larger air spaces with a much smaller surface area for gas exchange, so the person is breathless.
• Lung cancer: carcinogens in tar cause mutations in lung cells, leading to uncontrolled cell division. Smoking also raises the risk of cancers of the mouth, throat, oesophagus, bladder and pancreas.

Worked example: relative risk

In a study, the death rate from lung cancer was 12 per 100 000 non-smokers each year and 228 per 100 000 heavy smokers each year. How many times greater is the risk for heavy smokers?
relative risk = 228 ÷ 12 = 19

Answer: heavy smokers were 19 times more likely to die of lung cancer

Cardiovascular disease

Smoking is a major risk factor for cardiovascular disease (coronary heart disease, heart attacks and strokes).

• Chemicals in smoke damage the lining of the arteries, so fatty material builds up more easily and the arteries narrow.
• Nicotine raises the heart rate and blood pressure, so the heart works harder.
• Carbon monoxide reduces the oxygen carried by the blood, so the heart has to pump more blood to supply enough oxygen.

Key fact: Smoking increases the risk of blood clots forming in narrowed arteries, which can block a coronary artery (heart attack) or an artery in the brain (stroke).

Smoking in pregnancy

Carbon monoxide from smoke passes into the mother's blood, so less oxygen reaches the fetus through the placenta. The fetus does not grow as well. Smoking in pregnancy increases the risk of premature birth, low birth weight and stillbirth.

Worked example: percentage change

In a study, babies of non-smokers had a mean birth mass of 3.40 kg. Babies of mothers who smoked 20 a day had a mean birth mass of 3.06 kg. Calculate the percentage decrease.
decrease = 3.40 − 3.06 = 0.34 kg
percentage decrease = (0.34 ÷ 3.40) × 100 = 10%

Answer: 10% lower birth mass

Common mistakes

• Saying nicotine causes lung cancer. The carcinogens in tar cause cancer; nicotine is the addictive substance.
• Saying carbon monoxide "blocks the lungs". It combines with haemoglobin, so less oxygen is carried in the blood.
• Saying smoking "makes the alveoli smaller". In emphysema alveolus walls break down, giving a smaller surface area.
• Thinking a high relative risk means every smoker gets the disease. It shows a higher chance, not a certainty.

Revision questions

Try these, then check your answers below each one.

Question 1. Which substance in tobacco smoke is addictive? (Choose from: Tar, Carbon monoxide, Nitrogen, Nicotine.)

Answer: Nicotine

Working: Nicotine is the addictive substance.

Question 2. True or false? Smoking during pregnancy increases the risk of a baby having a low birth weight.

Answer: True

Working: True. Less oxygen reaches the fetus, so it grows less well.

Question 3. Lung cancer deaths were 13 per 100 000 non-smokers and 260 per 100 000 heavy smokers each year. How many times greater is the death rate for heavy smokers?

Answer: 20

Working: 260 ÷ 13 = 20 times greater.

Related lessons

• Previous lesson: 7.2 Cancer
• Next lesson: 7.4 Diet, Exercise, and Disease
• In this chapter: 7.1 Non-Communicable Diseases
• In this chapter: 7.5 Alcohol and Other Carcinogens

Continue in the full course

This lesson is section 7.3 (AGCBH0703) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.