Alveoli, Exercise and Smoking

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 2.48 — How alveoli are adapted for gas exchange by diffusion
• 2.49 — Biological consequences of smoking for the lungs and circulatory system, including coronary heart disease
• 2.50 — Practical: investigate breathing in humans, including carbon dioxide release and the effect of exercise (required practical)

Specification section 2(g) Gas exchange — also taught in The Leaf: Structure and Gas Exchange, The Thorax and Ventilation, Why Transport Systems Exist, and the Two Plant Vessels, Gas Exchange in Plants, Day and Night.

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Your two lungs weigh about a kilogram and would fit in a shoebox, and the surface inside them is roughly the size of a tennis court. That is not a curiosity — it is the entire design. Gas exchange happens by diffusion, and diffusion is fast over a large area and a short distance and hopeless otherwise. Every feature of an alveolus is an attempt to win on one of those terms.

The four adaptations, and which factor each one buys

1. HUNDREDS OF MILLIONS OF ALVEOLI, each a tiny sphere: an enormous total surface area, so a great many molecules can cross at once.
2. WALLS ONE CELL THICK, and the capillary wall one cell thick too: a very short diffusion distance, so each molecule completes the crossing almost instantly.
3. A DENSE CAPILLARY NETWORK: blood constantly carries oxygen away and brings carbon dioxide, so the concentrations in the blood never have time to match those in the air — the gradient stays steep.
4. VENTILATION: breathing constantly replaces the air in the alveoli, so the oxygen in there never runs down and the carbon dioxide never builds up. This maintains the gradient from the other side.
5. The last two matter more than students expect. Surface area and thinness are fixed features; the gradient has to be actively maintained, and it is maintained from both directions at once.

Exercise makes the demand jump. Muscles respire faster, so they use oxygen faster and produce carbon dioxide faster. The body responds by increasing both the RATE of breathing — more breaths per minute — and the DEPTH, so more air moves per breath. Both changes deliver more oxygen to the alveoli and remove more carbon dioxide, and they persist after exercise stops because the lactic acid built up during it still has to be broken down.

What smoking does, substance by substance

1. TAR coats the airways and paralyses the cilia — the tiny hairs that normally sweep mucus, dust and bacteria up and out. Mucus then collects in the lungs, which produces the persistent cough and makes infection far more likely: chronic bronchitis.
2. TAR also contains carcinogens, substances that cause mutations in the DNA of the cells lining the airway, and so lung cancer.
3. SMOKE damages the walls between alveoli until they break down and merge into fewer, larger spaces. That is emphysema, and the consequence is exact: less total surface area, so less gas exchange, so breathlessness on the smallest effort.
4. CARBON MONOXIDE binds to haemoglobin far more strongly than oxygen does, and does not easily let go. Every molecule that binds is a red blood cell that can carry less oxygen, so the heart must work harder to deliver the same amount — and in pregnancy the fetus is supplied with less oxygen, so babies are smaller.
5. NICOTINE is the addictive substance, and it also raises heart rate and blood pressure and narrows blood vessels. Together with damage to the artery lining this encourages fatty deposits in the coronary arteries, restricting blood flow to the heart muscle itself — coronary heart disease, and ultimately a heart attack.

Notice that only two of those five are lung problems in the ordinary sense. Carbon monoxide and nicotine act on the blood and the circulation, which is why smoking damages the heart as well as the lungs — and why an exam question about smoking will very often be asking about the circulatory system rather than about breathing at all.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

Learn this definition · Gas exchange

The diffusion of oxygen from the alveolar air into the blood, and of carbon dioxide from the blood into the alveolar air, each moving down its own concentration gradient.

The alveolar adaptations, each with the factor it improves

Hundreds of millions of alveoli

an enormous total surface area, so many molecules can diffuse at the same time

Wall one cell thick

a very short diffusion distance between air and blood

Dense capillary network

constantly removes oxygen and delivers carbon dioxide, keeping the concentration gradients steep

Ventilation

constantly replaces the alveolar air, maintaining the gradients from the air side

Moist lining

gases must dissolve before they can diffuse across the cell membrane

The four harmful components of tobacco smoke — learn the substance AND its effect

Tar

paralyses the cilia so mucus collects, causing smoker's cough and bronchitis; also contains carcinogens that cause lung cancer

Carbon monoxide

binds strongly to haemoglobin, so the blood carries less oxygen; the heart works harder and a fetus receives less oxygen

Nicotine

the addictive component; raises heart rate and blood pressure and narrows blood vessels

Smoke particles generally

damage and break down alveolar walls, causing emphysema and a permanent loss of surface area

Why emphysema causes breathlessness — the chain that earns the marks

1. Smoke damages the walls between alveoli, so they break down and merge.
2. Many small alveoli become fewer, larger air spaces.
3. This greatly reduces the total surface area available for gas exchange.
4. Less oxygen diffuses into the blood per breath, so the person becomes breathless even on light exertion.

Required practical 2.50 — investigating breathing and the effect of exercise

1. Measure resting breathing rate by counting breaths for one minute while sitting still, and repeat three times to obtain a mean.
2. Exercise for a fixed time — for example three minutes of step-ups at a set rate — then immediately count breaths for one minute again.
3. Continue counting each minute afterwards until the rate returns to the resting value, and record the recovery time.
4. To show carbon dioxide is released, breathe out through a delivery tube into limewater; it turns milky, while limewater that room air is drawn through stays clear.
5. Plot breathing rate against time, marking the exercise period, and compare rest, exercise and recovery.

Variables

Independent (changed) — whether the person is at rest or has exercised, and the time since exercise
Dependent (measured) — breathing rate in breaths per minute

Sources of error

Model answer [4 marks]

Explain how the alveoli are adapted for rapid gas exchange. [4]

There are hundreds of millions of alveoli, giving an enormous total surface area for diffusion. The alveolus wall and the capillary wall are each one cell thick, so the diffusion distance is very short. A dense capillary network carries oxygen away and brings carbon dioxide, keeping the concentration gradients steep. Ventilation constantly replaces the air in the alveoli, maintaining those gradients from the air side.

Model answer [4 marks]

Explain why a person who smokes may become breathless when climbing stairs. [4]

Smoke damages the walls between the alveoli, which break down and merge into fewer, larger spaces. This reduces the total surface area available for gas exchange, so less oxygen diffuses into the blood. Carbon monoxide in the smoke also binds to haemoglobin, so the blood carries less oxygen than it should. Less oxygen reaches the muscles, so less aerobic respiration is possible and the person becomes breathless on exertion.

Mark-losing trap. Name the substance AND the effect. 'Smoking damages the lungs' scores nothing; tar, carbon monoxide and nicotine each do something specific.

Mark-losing trap. Emphysema reduces surface area — it does not block the airways. That is the phrase the mark scheme is looking for.

Mark-losing trap. Carbon monoxide and nicotine damage the CIRCULATION. Many smoking questions are really about the heart, not the lungs.

Mark-losing trap. Breathing rate and depth both increase during exercise. Answers that mention only rate lose half the marks available.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · State [1 mark] — Which component of tobacco smoke binds to haemoglobin and reduces the amount of oxygen the blood can carry?
2. Grade 7 · Explain [2 marks] — During exercise, both the rate and the depth of breathing increase. Explain why.
3. Grade 8 · Explain [4 marks] — A long-term smoker develops emphysema and becomes breathless walking up a short flight of stairs. Select every statement that belongs in a full-mark explanation.
4. Grade 9 · Calculate [4 marks] — A pair of lungs contains about 300 million alveoli, each approximately a sphere of diameter 0.30 mm. The surface area of a sphere is πd². Calculate the total alveolar surface area in m², to two significant figures.
5. 9+ · Analyse [5 marks] — A smoker and a non-smoker of the same age and fitness both exercise for three minutes. Both reach a similar peak breathing rate, but the smoker's breathing takes far longer to return to its resting value, and blood tests show that the smoker's blood carried less oxygen throughout. Select every statement that belongs in a full-mark explanation.

The people behind this science

Three ways into the same idea — the one who proved smoking kills, without ever running an experiment, and the one who found which part of the air a body actually takes, and the one who learned what long exposure does to a body. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Richard Doll — the one who proved smoking kills, without ever running an experiment

You cannot assign half a population to smoke for thirty years, so the harm on this page had to be proved another way. Doll expected the rise in lung cancer to be caused by tarred roads; his data said tobacco, and he gave up his own cigarettes before publishing. He and Bradford Hill then followed 34,000 doctors for fifty years, and answered every objection — including the serious argument that smokers might simply be different people — with evidence rather than indignation.

• “What did you expect the cause of the rise in lung cancer to be?”
• “How do you prove something causes harm when an experiment is impossible?”
• “Why follow 34,000 doctors for fifty years instead of just asking patients?”
• “How did you answer the claim that smokers might just be a different sort of person?”
• “What did your statistics never tell you about what smoke actually does inside a lung?”

Antoine Lavoisier — the one who found which part of the air a body actually takes

Before Lavoisier, air was thought to be a single substance, and there was no way to say what breathing did to it. He showed that only one component is consumed and another is given back — which is why an alveolus needs two gradients running in opposite directions at once, and why ventilation has to keep replacing the air rather than simply filling the lungs.

• “How did you show that only part of the air is used up by breathing?”
• “What is given back to the air in exchange for what is taken?”
• “Why must fresh air keep arriving rather than simply filling the chest once?”
• “What did you think happened to the air once it was inside the body?”

Marie Curie — the one who learned what long exposure does to a body

Curie worked for years with materials whose danger nobody suspected, carrying tubes of radium in her pockets, and the illness that killed her almost certainly came from that exposure. Her case is the clearest example of the pattern this lesson describes in smoking: a harm that is invisible at the time, accumulates with dose, appears only after many years, and is denied by almost everyone while it is happening.

• “How can something be doing harm for years before anyone can see it?”
• “Why was the danger of your own materials so slow to be accepted?”
• “Does it matter how much of a harmful thing you are exposed to, or only that you are?”
• “What would have convinced you earlier that you were being harmed?”

Carry on through the course

• Previous lesson: The Thorax and Ventilation
• Next lesson: Why Transport Systems Exist, and the Two Plant Vessels
• Levels of Organisation — From organelle to organism — the five-step ladder that every later topic in biology is built on.
• Comparing Cells, and Stem Cells — What plant and animal cells share and where they differ — then why a cell specialising is one of the most powerful ideas in biology.
• Carbohydrates, Proteins and Lipids — The three big food molecules — what they are made of, what they are built from, and how to test for them.
• Enzymes: Catalysts With a Shape — Why a protein with a hole in it speeds up a reaction, and why heat destroys that ability permanently.
• Enzymes and pH — Why acid ruins one enzyme and is the only condition another will work in — and how to find an enzyme's best pH by experiment.
• All of Biology · Biology key terms · required practicals · Incandio Science · The 4BI1 specification