What are pathogens?

Pathogens are defined as microorganisms that have the capability of causing disease in their host. This definition encompasses a variety of organisms, including bacteria, viruses, fungi, and parasites. These agents can invade the body, disrupt normal functions, and provoke an immune response, which can lead to illness.

While the other choices mention specific categories or types of organisms, they do not encompass the broader definition of what pathogens are. For instance, the choice regarding viruses that only affect plants is too narrow, as it excludes other pathogens that affect animals and humans. The mention of healthy bacteria pertains to normal flora, which are beneficial and do not cause disease, thus falling outside the definition of pathogens. The reference to components of the immune system does not relate to pathogens at all, as it describes the body's defense mechanisms rather than the organisms that cause diseases. Therefore, identifying pathogens as microorganisms that can cause disease accurately captures the essence of their impact on health.