Edexcel IGCSE Biology · Spec 2.49
Smoking and the Lungs
The harmful substances in tobacco smoke and their effects on the lungs, including emphysema and disease.
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Smoking and the Lungs
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Explained
What tobacco smoke does, substance by substance
Four harmful components are examinable, and each causes a different problem by a different mechanism. Learning them as four separate chains is far more reliable than remembering that smoking is bad for you.
Tar
Tar is sticky and collects in the airways. It damages the cilia, the tiny hairs that normally sweep mucus and trapped dirt up and out of the lungs.
With the cilia damaged, mucus is not removed, so it builds up. The body coughs to shift it, which is smoker's cough, and the airways become inflamed, which is bronchitis. The trapped mucus and dirt also mean bacteria stay in the lungs, so chest infections are more common.
Carcinogens
Tobacco smoke contains carcinogens, chemicals that cause cancer by damaging the DNA in cells. Damaged DNA can make a cell divide uncontrollably, forming a tumour. This is why smoking is linked to lung cancer, and to cancers of the mouth and throat.
Carbon monoxide
Carbon monoxide binds to haemoglobin in red blood cells in place of oxygen, and it binds more strongly. Haemoglobin carrying carbon monoxide cannot carry oxygen, so less oxygen reaches the tissues.
In a pregnant woman this matters twice over, because the fetus receives less oxygen too, which can lead to low birth mass.
Emphysema
Repeated coughing and inflammation break down the walls of the alveoli, so many small air sacs become fewer large ones.
That reduces the total surface area available for gas exchange, so less oxygen diffuses into the blood. Breathlessness follows, at first only on exertion and eventually all the time.
Nicotine
Nicotine is the addictive substance, which is why stopping is difficult. It also narrows blood vessels and raises heart rate and blood pressure, increasing the risk of heart disease and stroke.
What the mark scheme accepts and rejects
An Edexcel International GCSE Biology mark scheme asks why smokers use oxygen at a lower rate, for three marks, and offers seven routes: a lower rate of oxygen use, tar, emphysema or mucus building up or cilia damaged, less surface area of the alveoli, less diffusion of oxygen into the blood, carbon monoxide binding to haemoglobin, and narrowing of arteries reducing blood flow.
Its guidance accepts less oxygen uptake, accepts alveoli walls breaking down, deforming or being damaged, and accepts the converse throughout for a non smoker.
Each of those is a link in a chain rather than a separate fact. The examiners are looking for the route from the substance to the consequence, and a three mark question wants three steps of it.
A report on the same paper makes the point in another context, noting that a response would have been more accurate if the candidate had written about less respiration, less growth and less protein rather than describing the effect in general terms. Naming what the shortage of oxygen prevents is what turns a description into an explanation.
Structuring the answer
Name the substance, say what it damages, and say what that damage prevents. Tar damages the cilia, so mucus is not removed, so infections are more likely. Carbon monoxide binds to haemoglobin, so less oxygen is carried, so less aerobic respiration takes place.
Three clauses each time. It is the same shape as the chain in every other topic where the examiners award marks for links, and it is the reason the mark schemes here run to seven points for three marks.
Spec 2.49
What you need to know
- Name the harmful substances in tobacco smoke
- Describe their effects on the lungs
- Link smoking to disease
Active recall
Quick check
Answer each question before opening the answer.
Name two harmful substances in cigarette smoke and their effects.
Any two of: tar (carcinogen), nicotine (addictive, raises heart rate), carbon monoxide (reduces oxygen carried by the blood).
Name a disease linked to smoking.
Lung cancer, emphysema, chronic bronchitis or coronary heart disease.
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