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How do exercise and smoking affect breathing and the lungs?

Explain the effects of physical activity on breathing and the harmful effects of tobacco smoke

A focused answer to the O-Level Biology outcome on exercise and smoking. Why breathing rate and depth rise during exercise, and the harmful effects of tar, nicotine and carbon monoxide in tobacco smoke.

Generated by Claude Opus 4.88 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

SEAB wants you to explain why breathing rate and depth increase during exercise and how this benefits the body, and to describe the harmful effects of the main substances in tobacco smoke (tar, nicotine and carbon monoxide). This connects respiration, gas exchange and human health.

The answer

Why breathing changes during exercise

When you exercise, your muscles work harder and respire faster to release more energy. This means they use more oxygen and produce more carbon dioxide. The increase in carbon dioxide in the blood is detected by the body, which responds by increasing:

  • the breathing rate (more breaths per minute), and
  • the depth of breathing (more air per breath).

How this helps the body

Breathing faster and more deeply brings more oxygen into the lungs each minute and removes the extra carbon dioxide. This supplies the muscles with the oxygen needed for increased aerobic respiration, so more energy is released, and it prevents a harmful build-up of carbon dioxide. The heart also beats faster to carry the oxygen and carbon dioxide more quickly.

The harmful substances in tobacco smoke

Tobacco smoke contains many harmful substances. Three important ones are:

Tar
A sticky brown substance that collects in the airways and lungs. It is a carcinogen (causes lung cancer), damages the airways (contributing to bronchitis and the destruction of alveoli in emphysema), and paralyses or destroys the cilia that sweep mucus and dirt out of the airways.
Nicotine
An addictive substance that makes smoking hard to give up. It also raises the heart rate and blood pressure and narrows blood vessels.
Carbon monoxide
A gas that binds to haemoglobin in red blood cells in place of oxygen, reducing the amount of oxygen the blood can carry, so the body gets less oxygen.

Diseases linked to smoking

Long-term smoking is linked to lung cancer, chronic bronchitis (inflamed, mucus-filled airways), emphysema (destroyed alveoli, reducing surface area for gas exchange), and coronary heart disease.

Examples in context

Example 1. Recovering after a run. After exercise, breathing stays fast for a while to take in the extra oxygen needed to break down lactic acid built up by any anaerobic respiration, repaying the oxygen debt before breathing returns to normal.

Example 2. A smoker with a cough. Tar paralyses the cilia that normally sweep mucus and dirt out of the airways. Mucus and trapped dirt build up, so the smoker coughs to clear the airways, the familiar smoker's cough, and infections become more likely.

Try this

Q1. State two ways breathing changes during exercise. [2 marks]

  • Cue. The breathing rate increases (more breaths per minute) and the depth of breathing increases (more air per breath).

Q2. State one harmful effect of carbon monoxide in tobacco smoke. [1 mark]

  • Cue. It binds to haemoglobin in place of oxygen, reducing the amount of oxygen the blood can carry.

Q3. Explain why a smoker's airways become blocked with mucus. [2 marks]

  • Cue. Tar paralyses or destroys the cilia that normally sweep mucus and dirt out, so mucus builds up in the airways.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original5 marksDuring exercise, a person's breathing rate and depth both increase. Explain why this happens and how it helps the body.
Show worked answer →

During exercise, the muscles work harder and respire faster, so they use more oxygen and produce more carbon dioxide. The rise in carbon dioxide is detected by the body, which increases the breathing rate and depth.

Breathing faster and more deeply brings more air, and so more oxygen, into the lungs each minute, and removes the extra carbon dioxide. This supplies the muscles with the extra oxygen needed for increased aerobic respiration to release more energy, and prevents a harmful build-up of carbon dioxide.

Markers reward more respiration in the muscles producing more carbon dioxide and using more oxygen, the increased breathing supplying oxygen and removing carbon dioxide, and the link to releasing more energy.

Original4 marksTobacco smoke contains tar, nicotine and carbon monoxide. State one harmful effect of each of these three substances on the body.
Show worked answer →

Tar collects in the lungs and airways, where it is a carcinogen (causes lung cancer) and damages the airways, contributing to bronchitis and the destruction of alveoli (emphysema). It also paralyses or destroys the cilia that clean the airways.

Nicotine is an addictive substance that makes smoking hard to give up; it also raises heart rate and blood pressure and narrows blood vessels.

Carbon monoxide binds to haemoglobin in red blood cells in place of oxygen, reducing the amount of oxygen the blood can carry.

Markers reward one correct harmful effect for each of the three substances: tar (cancer or airway damage), nicotine (addiction or raised heart rate), and carbon monoxide (reduces oxygen carried by the blood).

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