Respiratory system: Smoking.

The idea

Smoking introduces tar, carbon monoxide, nicotine and irritants into the respiratory tract. Tar paralyses and destroys cilia, so mucus, dust and pathogens are not swept upwards and accumulate, causing coughing and increasing infection risk. Irritants trigger inflammation and narrowing of the airways, raising airway resistance and the work of breathing. Tar and chemicals destroy alveolar walls, reducing alveolar surface area for gaseous exchange. Carbon monoxide binds haemoglobin more readily than oxygen, forming carboxyhaemoglobin and reducing oxygen transport to working muscles. Nicotine increases heart rate and narrows blood vessels. Together these effects lower aerobic capacity, so a smoker fatigues sooner during endurance exercise.

What earns the marks

• Tar paralyses and destroys cilia, so mucus and pathogens accumulate and infection risk rises.
• Irritants cause inflammation and narrowing of airways, increasing airway resistance and the work of breathing.
• Tar and chemicals destroy alveolar walls, reducing alveolar surface area for gaseous exchange.
• Carbon monoxide binds haemoglobin more readily than oxygen, forming carboxyhaemoglobin and reducing oxygen transport.
• Nicotine raises heart rate and narrows blood vessels, increasing cardiac and respiratory demand.
• Reduced oxygen transport lowers aerobic capacity, so fatigue occurs sooner during endurance exercise.

Common mistakes and how to put them right

• Saying smoking reduces the number of red blood cells.

  Put it right: Carbon monoxide binds haemoglobin, so the blood carries less oxygen even though red blood cell count is unchanged.

• Thinking cilia grow stronger to cope with smoke.

  Put it right: Cilia are paralysed and destroyed, so mucus clearance fails.

• Believing tar only discolours the lungs.

  Put it right: It also destroys alveolar walls and reduces surface area for gaseous exchange.

• Confusing nicotine with carbon monoxide.

  Put it right: Nicotine raises heart rate and narrows vessels, while carbon monoxide reduces oxygen transport.

Exam tips

• Name the harmful component, then state its specific effect on a named respiratory structure.
• Use the chain cilia destroyed, mucus trapped, infection risk, airway resistance, reduced gaseous exchange for full-mark explanations.
• Distinguish clearly between effects on the airways, the alveoli and oxygen transport when answering comparison questions.