The shape of the lesson
By the end of the lesson, learners can
- Follow the air down the tree: The lab opens on the whole system.
- Cut through the airway walls: Pick trachea, bronchus, bronchiole and alveolus in turn and click each tissue in the wall.
- Keep the surface clean: Watch the particles fall onto the mucus and drift towards the throat.
- Recognise them under the microscope: You must identify these tissues and airways in light micrographs and electron micrographs, and draw plan diagrams of the trachea and bronchus walls.
- Trachea: C-shaped cartilage rings, ciliated epithelium, goblet cells, glands.
- Bronchus: cartilage plates, otherwise like the trachea.
- Bronchiole: no cartilage, relatively more smooth muscle, few goblet cells.
- Alveolus: squamous epithelium, elastic fibres, capillaries only.
One picture every idea returns to
Air passes through the trachea, which divides into two bronchi, one to each lung; these branch into many bronchioles, which end in clusters of alveoli surrounded by a capillary network. Cartilage is found as C-shaped rings in the trachea and irregular plates in the bronchi, but not in bronchioles or alveoli. Ciliated epithelium with goblet cells lines the trachea, bronchi and larger bronchioles. Smooth muscle and elastic fibres are in the walls of all the airways, with relatively most smooth muscle in the bronchioles. Squamous epithelium forms the alveolar walls, which are wrapped in capillaries. Goblet cells and mucous glands secrete mucus that traps dust, pollen and bacteria, and the cilia beat to sweep the mucus up to the throat, where it is swallowed.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, From trachea to alveolus, the walls change.. Air reaches the alveoli through a branching tree of airways. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 11 min | Teach and check: Follow the air down the tree | The lab opens on the whole system. Project tab 1 of the lab (Gas exchange lab, the gas exchange system) and let a student drive it while the class predicts. | Whole class, then pairs |
| 11 to 17 min | Teach and check: Cut through the airway walls | Pick trachea, bronchus, bronchiole and alveolus in turn and click each tissue in the wall. Project tab 2 of the lab (Gas exchange lab, tissues in the airway walls) and let a student drive it while the class predicts. | Pairs |
| 17 to 23 min | Teach and check: Keep the surface clean | Watch the particles fall onto the mucus and drift towards the throat. Project tab 3 of the lab (Gas exchange lab, cilia and mucus) and let a student drive it while the class predicts. | Pairs |
| 23 to 30 min | Teach and check: Recognise them under the microscope | You must identify these tissues and airways in light micrographs and electron micrographs, and draw plan diagrams of the trachea and bronchus walls. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 20 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Recognise them under the microscope, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Bronchioles have no cartilage; that is the quickest way to tell a bronchiole from a bronchus on a slide. | Do not say the trachea has complete rings: the rings are C-shaped, and the gap at the back, next to the oesophagus, is bridged by smooth muscle. |
| Cilia do not trap particles and they do not make mucus. | Mucus (from goblet cells and mucous glands) traps; cilia move the mucus. Keep the two jobs separate in your answer. |
The gas exchange system and its airways: worksheet
6 questions, 20 marks. Written in the style of the papers; no past paper question is reproduced.
Name, in order, the structures that air passes through from the trachea to the site of gas exchange.
Describe the distribution of cartilage, goblet cells and smooth muscle in the trachea, bronchi and bronchioles.
Explain how goblet cells, mucous glands and ciliated epithelial cells work together to maintain the health of the gas exchange system.
Suggest why people who smoke for many years often have a persistent cough and frequent chest infections.
A student looks at a slide of lung tissue and sees a tube with a lining of columnar ciliated cells, a ring of smooth muscle and no cartilage, surrounded by many thin-walled air spaces. Identify the tube and the air spaces and give the evidence for each.
Describe the features you would include, and those you would leave out, when making a plan diagram of a transverse section of the trachea wall.
Answer key and marking notes
- Trachea, then a bronchus.
- Then bronchioles (branching into smaller bronchioles).
- Then the alveoli, where gas exchange with the capillary network occurs.
- Cartilage: C-shaped rings in the trachea, irregular plates in the bronchi, none in the bronchioles.
- Goblet cells: in the ciliated epithelium of the trachea and bronchi; few or none in bronchioles.
- Smooth muscle: in the walls of all three.
- It makes up a relatively larger proportion of the wall in the bronchioles.
- Goblet cells and mucous glands secrete mucus onto the airway lining.
- The sticky mucus traps dust, pollen and pathogens such as bacteria in the inhaled air.
- Cilia beat in a coordinated way to move the mucus up to the throat, where it is swallowed.
- So particles and pathogens are removed before they reach the alveoli, reducing infection and keeping the exchange surface clean.
- Tobacco smoke paralyses and destroys cilia, so mucus is not moved up the airways.
- Smoke increases mucus secretion by goblet cells and mucous glands, so mucus builds up.
- Coughing is the only way to remove the mucus, and bacteria trapped in it multiply, causing infections such as bronchitis.
- The tube is a bronchiole.
- Evidence: no cartilage (so not trachea or bronchus) but a ciliated lining and smooth muscle.
- The air spaces are alveoli: thin walls of squamous epithelium.
- Include clear, continuous outlines of each tissue layer: ciliated epithelium, smooth muscle, the C-shaped cartilage and the lumen.
- Draw the layers in the correct relative proportions and label them.
- Do not draw individual cells and do not shade.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which sequence shows the route taken by air from the larynx to the site of gas exchange?
- Atrachea, bronchus, bronchiole, alveolus
- Btrachea, bronchiole, bronchus, alveolus
- Cbronchus, trachea, bronchiole, alveolus
- Dtrachea, bronchus, alveolus, bronchiole
Which tissue is present in the walls of the trachea, bronchi and bronchioles but is absent from the walls of the alveoli?
- Asmooth muscle
- Belastic fibres
- Ccartilage
- Dsquamous epithelium
In a photomicrograph of the trachea lining, a student sees cup-shaped cells with pale-staining upper parts and no cilia, scattered among tall ciliated cells. What are these cells?
- Agoblet cells
- Bciliated epithelial cells
- Csquamous epithelial cells
- Dsmooth muscle cells
Where are the mucous glands of the gas exchange system found?
- Abeneath the epithelium of the trachea and bronchi
- Bin the walls of the alveoli
- Con the surface between the cilia
- Dinside the rings of cartilage
The table shows the tissues seen in transverse sections of four different airways, W, X, Y and Z. Which section is a bronchiole?
- AZ
- BW
- CX
- DY
Samples of bronchus lining from long-term smokers had fewer ciliated cells and more goblet cells than samples from non-smokers. Which consequence follows from these changes?
- Amucus is made faster than it is removed, so it collects with trapped bacteria
- Bless mucus is made, so more dust reaches the alveoli unhindered
- Cthe extra goblet cells take over the job of moving mucus upwards
- Dthe airway widens, so air reaches the alveoli more easily
In a photomicrograph of the trachea at a magnification of ×40, the cartilage ring measures 18 mm across its thickness. What is the actual thickness of the cartilage?
- A450 μm
- B720 μm
- C45 μm
- D4.5 mm
In an inherited condition the cilia of the airways are present but cannot beat. Which problem would people with this condition be most likely to have?
- Arepeated chest infections, as mucus and trapped bacteria stay in the airways
- Bno mucus at all, as goblet cells need beating cilia to secrete
- Cslower diffusion of oxygen, as alveoli need cilia to exchange gases
- Dcollapsed bronchi, as cilia hold the cartilage plates in place
Quiz key
The trachea divides into two bronchi, which branch into many bronchioles, and the bronchioles end in alveoli where gas exchange happens. Bronchioles are smaller than bronchi, so they cannot come before them; the trachea is the first tube below the larynx, not the bronchus; and alveoli are the blind-ended sacs at the end of the tree, so nothing comes after them.
Smooth muscle is in all the airway walls, relatively thickest in the bronchioles, but the alveolar wall has none. Elastic fibres are also found around the alveoli, so they are not absent there. Cartilage is absent from the bronchioles as well, so it fails the first part. Squamous epithelium is the alveolar lining itself, not a tissue of the trachea or bronchi.
Goblet cells are shaped like a cup and their upper part is filled with mucus, which stains pale; they have no cilia. Ciliated epithelial cells carry the cilia, so they are the tall cells around them. Squamous cells are thin and flat and line the alveoli, not the trachea. Smooth muscle cells are spindle-shaped and lie deeper in the wall, not in the lining.
Mucous glands lie in the submucosa beneath the epithelium of the trachea and bronchi and secrete mucus through ducts onto the lining. The alveolar wall has only squamous epithelium, elastic fibres and capillaries, with no glands. The mucus-secreting cells that sit on the surface between ciliated cells are goblet cells, not glands. Cartilage is a supporting tissue with no glands inside it.
Z has no cartilage, a ciliated lining and a thick layer of smooth muscle: a larger bronchiole. W has cartilage plates, so it is a bronchus. Y has a C-shaped ring, so it is the trachea. X has no cartilage, no cilia and no smooth muscle, which fits an alveolus rather than an airway.
More goblet cells secrete more mucus, while fewer ciliated cells move less of it towards the throat, so mucus builds up with the bacteria trapped in it, leading to coughing and infections such as bronchitis. Mucus production rises, not falls. Goblet cells have no cilia, so they cannot move mucus. Nothing in these changes widens the airway; extra mucus narrows it.
Actual size = 18 mm / 40 = 0.45 mm = 450 μm. 720 comes from multiplying 18 by 40 instead of dividing. 45 μm is a factor of ten too small, an error in converting mm to μm (1 mm = 1000 μm). 4.5 mm is ten times too large and also bigger than the image itself, which is impossible at a magnification greater than 1.
Cilia sweep mucus towards the throat; if they cannot beat, mucus and the pathogens trapped in it stay in the airways, so infections recur. Goblet cells secrete mucus whether or not cilia beat. Alveoli have no cilia, and gas exchange depends on diffusion across squamous epithelium. Cartilage supports the bronchi without any help from cilia.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.