Pathogens — Bacteria and Viruses

This lesson covers bacterial and viral pathogens as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the structure of bacteria and viruses, how they cause disease and be able to describe specific examples including Salmonella, HIV and TMV.

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What Are Pathogens?

A pathogen is a microorganism that causes disease. Pathogens are parasites — they live on or inside a host organism and cause damage to the host while benefiting themselves (by gaining nutrients or a place to reproduce).

There are four types of pathogen: bacteria, viruses, fungi and protists. This lesson focuses on bacteria and viruses.

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Bacteria

Structure of a Bacterial Cell

Bacteria are prokaryotic organisms. They are much smaller than eukaryotic cells (typically 1–5 μm in length) and have a simpler structure: