Lesson 4 of 6 / Respiration in humans
Link smoke components to effects
Why do nicotine, tar and carbon monoxide need different explanations?
I can explain the major biological effects of the three named tobacco-smoke components.
I can explain effects of nicotine, tar and carbon monoxide.Syllabus
Syllabus K325, Topic 6(d). Explain effects of nicotine, tar and carbon monoxide.
About 4 min
Make a guess. You are not marked.
Cigarette smoke reduces how much oxygen your blood can carry. Which part of the smoke does this?
Show the answer
Carbon monoxide, which binds to haemoglobin.
Carbon monoxide binds strongly to haemoglobin, so less haemoglobin is free to carry oxygen.
The key idea
Nicotine affects dependence and circulation; tar damages airways; carbon monoxide reduces oxygen carriage.
These are qualitative teaching models. Counts and dimensions do not represent an exposure dose or predict an individual outcome.
Explanation
Nicotine is addictive. It stimulates responses that increase heart rate and constrict some blood vessels, raising blood pressure and increasing the work of the heart. Its effects are different from tar coating the airways.
Tar is a mixture containing carcinogenic substances. It can damage cilia, so mucus and trapped particles are cleared less effectively. Mucus accumulation and airway irritation contribute to chronic bronchitis and increased respiratory problems.
Long-term exposure to tobacco smoke can damage alveolar walls and contribute to emphysema. Loss of walls reduces gas-exchange area, and loss of elastic recoil makes expiration less effective. Carcinogens can damage genetic material and increase the risk of cancer.
Carbon monoxide binds strongly to haemoglobin, forming carboxyhaemoglobin and reducing the capacity for oxygen carriage. Less oxygen can be supplied to respiring tissues. Carbon monoxide does not need to destroy every red cell to produce this effect.
An exam explanation should connect substance -> biological change -> consequence. The three components are not interchangeable labels, and a risk factor does not mean every exposed person develops the same disease.
Step by step
- 1
Identify the substance
Use nicotine, tar or carbon monoxide rather than only "smoke".
- 2
Name its target
For example, nicotine affects circulatory responses; tar affects airways; carbon monoxide binds haemoglobin.
- 3
Explain the consequence
Connect the target effect to reduced clearance, oxygen delivery, exchange area or increased disease risk.
Worked example
Reduced oxygen carriage
Explain how carbon monoxide in inhaled smoke can reduce oxygen delivery even when the lungs receive air.
One way to explain it
Carbon monoxide crosses into the blood and binds strongly to haemoglobin. This leaves less haemoglobin available to carry oxygen, so blood can deliver less oxygen to body cells despite air entering the lungs.
Why this answer works
- The affected step is oxygen transport in blood.
- Binding to haemoglobin is the mechanism.
- Ventilation alone does not guarantee normal oxygen delivery.
Watch out for this
A student says: "Nicotine, tar and carbon monoxide all harm the body by blocking the trachea." What is wrong with this?
Show the answer
They have different targets. Explain nicotine through dependence and circulation, tar through airway and tissue damage, and carbon monoxide through haemoglobin binding.
Check your understanding
Cilia are damaged and mucus accumulates in the airways. Which explanation best links cause and effect?
Show the answer
Tar damages cilia, reducing movement of mucus towards the throat.
Poorer clearance leaves mucus and trapped material in the airways.
Quick recall
Why do nicotine, tar and carbon monoxide need different explanations?