# Tuberculosis (TB) is a communicable disease caused by the bacterium Mycobacterium tuberculosis. It is spread when an infected person coughs or sneezes, releasing droplets into the air. Explain how TB spreads from one person to another and describe two ways the human body attempts to prevent the pathogen from causing infection once it has been inhaled.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 5.2 Pathogens and infection · Explain · 5 marks

> Tuberculosis (TB) remains one of the leading infectious diseases worldwide. It is caused by the bacterium Mycobacterium tuberculosis and primarily affects the lungs. The disease is most prevalent in overcrowded living conditions where people are in close proximity for extended periods.

## Mark scheme (5 marks)

1. TB is spread through the air via droplets / aerosols released when an infected person coughs or sneezes (droplet transmission / airborne transmission)
2. Overcrowding / close contact increases the risk of transmission because droplets travel easily between people in close proximity
3. Mucus in the airways (produced by goblet cells) traps the bacteria / pathogens, acting as a physical barrier
4. Cilia (hair-like structures on ciliated epithelial cells) waft / move the mucus (and trapped bacteria) away from the lungs towards the throat where it is swallowed
5. White blood cells / phagocytes engulf and destroy any bacteria that reach the lungs / tissues by phagocytosis

## Key terms

- [communicable disease](https://www.gradenine.co.uk/glossary/communicable-disease)
- [pathogen](https://www.gradenine.co.uk/glossary/pathogen)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/tuberculosis-tb-is-a-communicable-disease-0ab39720) · Published by Druglandscape Ltd.