What are pathogens?

Pathogens are defined as microorganisms that cause disease. This includes a variety of different types of organisms such as bacteria, viruses, fungi, and parasites. When these pathogens invade a host, they can disrupt normal bodily functions and lead to illness. The concept of pathogens encompasses a broad range of disease-causing agents, highlighting their role in infectious diseases and the various mechanisms through which they can affect health.

The other choices describe specific types of microorganisms or their roles but do not accurately capture the broader definition of pathogens. For example, while viruses can be pathogens, stating that they can only survive in human hosts is too limiting and not a characteristic of all pathogens. Similarly, beneficial bacteria and fungi that break down organic material play important roles in ecosystems or health but do not fit the definition of pathogens, which specifically refers to disease-causing organisms.