The three key chemicals in tobacco smoke
| Chemical | Effect |
|---|---|
| Tar | A carcinogen that damages cilia lining the airways and causes lung cancer |
| Nicotine | An addictive stimulant that raises heart rate and blood pressure, narrowing arteries |
| Carbon monoxide | Binds irreversibly to haemoglobin, forming carboxyhaemoglobin, reducing the oxygen-carrying capacity of the blood |
Exam answers must match each chemical to its correct effect. A common error is attributing addiction to tar or cancer to nicotine.
Damage to the respiratory system
Tar settles on the lining of the airways and destroys the cilia, the tiny hair-like structures that sweep mucus and trapped particles up and out of the lungs. Without functioning cilia, mucus accumulates, blocking smaller airways and triggering a persistent cough (smoker's cough). Bacteria trapped in the mucus can cause repeated infections.
Long-term exposure leads to chronic bronchitis (inflammation and excess mucus in the bronchi) and emphysema (destruction of alveolar walls, reducing surface area for gas exchange). Together these are called chronic obstructive pulmonary disease (COPD). Tar is also a carcinogen, meaning it causes mutations in lung cells that can lead to uncontrolled cell division and lung cancer.
Effects on the cardiovascular system
Nicotine stimulates the release of adrenaline, which increases heart rate and blood pressure. It also causes blood vessels to narrow (vasoconstriction). Over time this damages artery walls and promotes the build-up of fatty deposits, increasing the risk of coronary heart disease and stroke.
Carbon monoxide reduces the amount of oxygen carried by the blood. The heart must work harder to deliver sufficient oxygen to tissues, further raising blood pressure. In pregnant women, carbon monoxide reduces oxygen delivery to the fetus, which can result in low birth weight.
Smoking during pregnancy
Carbon monoxide crosses the placenta and binds to fetal haemoglobin, reducing the oxygen supply to the developing baby. Nicotine constricts blood vessels in the placenta, further reducing nutrient and oxygen delivery. These effects can lead to low birth weight, premature birth and increased risk of complications.
This is a common Supplement-level question: link the specific chemicals to their mechanism of harm on the fetus rather than simply stating "smoking harms the baby".