What role does a pathogen play in relation to health?

A pathogen is an organism that can cause disease in its host. This includes bacteria, viruses, fungi, and parasites, which invade the body and disrupt normal biological processes. The presence of a pathogen can lead to various health issues, ranging from mild illnesses to severe conditions, depending on the type of pathogen and the host's health status.

In contrast, nutrients are substances that provide nourishment to cells, supporting their functions and overall health. While some microorganisms may play beneficial roles in maintaining health, particularly in the gut, pathogens do not support cell function; rather, they interfere with it, often leading to injury or dysfunction. Tissue repair is typically facilitated by the body's natural healing processes and immune response rather than by pathogens, which negatively impact health. Thus, the primary role of a pathogen is to cause disease, making this option the correct choice.