Microorganisms which cause diseases are called

Options

A. antigens
B. antibodies
C. pathogens
D. vectors.

Explanation

**Step-by-Step Solution:**

1. **Understanding Microorganisms**: Microorganisms are tiny living organisms that can only be seen under a microscope. They include bacteria, viruses, fungi, and protozoa.

2. **Identifying Disease-Causing Microorganisms**: Among these microorganisms, some are harmful and can cause diseases in humans, animals, and plants.

3. **Defining Key Terms**:
- **Antigen**: A substance that triggers an immune response in the body. It is not a disease-causing microorganism but rather something that the immune system reacts against.
- **Antibody**: A protein produced by the immune system in response to an antigen. Antibodies help to neutralize or destroy pathogens but are not the pathogens themselves.
- **Pathogen**: This is the correct term for microorganisms that cause diseases. Examples include bacteria (like those causing typhoid), viruses (like HIV), and protozoa (like Plasmodium causing malaria).
- **Vector**: An organism that transmits a pathogen from one host to another. While vectors can spread diseases, they are not the pathogens themselves.

4. **Conclusion**: The microorganisms that cause diseases are specifically referred to as **pathogens**.

**Final Answer**: Microorganisms which cause diseases are called **Pathogens**.

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