# Tuberculosis (TB) is a communicable disease caused by the bacterium Mycobacterium tuberculosis. It is spread by droplets released into the air when an infected person coughs or sneezes. Explain how TB spreads from one person to another and how the body's defences attempt to prevent infection once the bacteria have been inhaled.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.2 Pathogens and infection · Explain · 5 marks

> Tuberculosis (TB) is one of the world's leading infectious diseases. In crowded, poorly ventilated environments the disease spreads rapidly. Despite this, many people who inhale the bacterium do not develop symptoms.

## Mark scheme (5 marks)

1. TB is spread when an infected person coughs or sneezes, releasing droplets containing Mycobacterium tuberculosis into the air
2. Mucus in the airways traps the bacteria / pathogens before they can reach the lungs
3. Cilia waft the mucus (and trapped bacteria) upward towards the throat so it can be swallowed or expelled
4. Hydrochloric acid in the stomach destroys any bacteria that are swallowed
5. If bacteria reach the lungs, white blood cells / phagocytes can engulf and destroy them by phagocytosis

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-525c357d) · Published by Druglandscape Ltd.