Lesson 3 of 5 / 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 state the three named smoke components and their health effects.Syllabus
Syllabus K224 / K225, Topic 6(c). State the three named smoke components and their health effects.
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 makes the heart beat faster and narrows some blood vessels. This raises blood pressure and makes the heart work harder.
Tar contains substances that can cause cancer (carcinogens). Tar damages cilia, so mucus and trapped dirt are not cleared from the airways. Mucus builds up and the airways become irritated, which can lead to chronic bronchitis.
Smoking for many years can break down the walls of the alveoli. This is emphysema. With fewer walls, there is less surface for gas exchange, and the lungs spring back less well when you breathe out. Carcinogens in smoke can also damage DNA and cause cancer.
Carbon monoxide joins tightly to haemoglobin, forming carboxyhaemoglobin. That haemoglobin can no longer carry oxygen. So less oxygen reaches the cells that are respiring.
In an exam answer, link each substance to what it does and to the result. Nicotine, tar and carbon monoxide each cause different damage. A risk factor makes a disease more likely, but not every smoker gets the same disease.
Step by step
- 1
Name the substance
Say nicotine, tar or carbon monoxide, not just "smoke".
- 2
Say what it acts on
Nicotine acts on the heart and blood vessels. Tar acts on the airways. Carbon monoxide joins haemoglobin.
- 3
Give the result
Say what goes wrong: less mucus cleared, less oxygen carried, less surface for exchange, or a higher risk of disease.
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?