What are pathogens?

Explanation

**Step-by-Step Solution:**

1. **Definition of Pathogens**: Pathogens are microorganisms that cause diseases. They are responsible for various illnesses in humans, animals, and plants.

2. **Understanding Microorganisms**: Microorganisms are tiny living organisms that cannot be seen with the naked eye. They can only be observed under a microscope. Common types of microorganisms include bacteria, viruses, fungi, and protozoans.

3. **Types of Pathogens**: Pathogens can be classified into different categories based on their type:
- **Bacteria**: For example, *Salmonella typhi* causes typhoid fever.
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