Which statement about pathogens is true?

Options

A. All pathogens are non-parasitic.
B. All microorganisms are pathogens.
C. All pathogens are harmful to humans.
D. All pathogens are beneficial to humans.

Answer

To determine which statement about pathogens is true, we need to analyze each of the provided statements based on our understanding of pathogens.

### Step-by-Step Solution:

1. **Understanding Pathogens**:
- Pathogens are organisms that cause diseases. They can be bacteria, viruses, fungi, or protozoa.

2. **Evaluating the Statements**:
- **Statement 1**: "All pathogens are non-parasitic."
- This statement is false. Some pathogens are parasitic, meaning they live on or in a host organism and derive nutrients at the host's expense. Examples include certain protozoa and helminths.

- **Statement 2**: "All microorganisms are pathogens."
- This statement is also false. While some microorganisms are pathogens, many are beneficial to humans, such as those used in fermentation or in the production of antibiotics like penicillin.

- **Statement 3**: "All pathogens are harmful to humans."
- This statement is true. By definition, pathogens are disease-causing organisms, and thus they are harmful to humans.

- **Statement 4**: "All pathogens are beneficial to humans."
- This statement is false. Since pathogens cause diseases, they cannot be considered beneficial to humans.

3. **Conclusion**:
- The only true statement about pathogens is **Statement 3**: "All pathogens are harmful to humans."

### Final Answer:
The true statement about pathogens is: **"All pathogens are harmful to humans."**

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