Year 9 Science · Unit 1 · Lesson 4
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Learning Goals
Order the steps
Number the events from 1 to 6 to show the correct order. Event 1 = what happens first when a pathogen is breathed in through the nose.
| Order | Event |
|---|---|
| Cilia in the respiratory tract beat in coordinated waves, sweeping the mucus and trapped pathogen upward toward the throat. | |
| The pathogen is swallowed and reaches the stomach. | |
| The pathogen-laden mucus arrives in the stomach, where hydrochloric acid (pH 2) destroys most pathogens. | |
| The pathogen enters the nose and is filtered by nasal hairs, slowing its travel. | |
| The pathogen becomes stuck in the sticky mucus secreted by the mucous membranes lining the respiratory tract. | |
| The pathogen cannot penetrate intact mucous membranes and would need to be swallowed to continue into the body. |
Compare two
Complete the table to compare skin (physical barrier) and stomach acid (chemical barrier).
| Feature | Skin (physical barrier) | Stomach acid (chemical barrier) |
|---|---|---|
| Mechanism, how does it stop pathogens? | ||
| Where in the body does it act? | ||
| Types of pathogen it stops | ||
| How can this barrier be bypassed? | ||
| One specific chemical or structural feature that makes it effective |
1. Smokers have damaged cilia in their respiratory tracts. Using your knowledge of the mucociliary escalator, explain why smokers are more likely to develop lung infections than non-smokers.
2. Lactoferrin in breast milk is a chemical barrier that binds iron, making it unavailable to bacteria. Explain why removing the iron supply would help stop a bacterial infection.
Wrap Up
In one sentence, what was the main idea of this lesson?