Which of the following is considered a characteristic of a pathogen?

A pathogen is defined as any organism or agent that can cause disease. This definition emphasizes the role of a pathogen in instigating illness in a host, which may include plants, animals, and humans. While there are various types of pathogens, including bacteria, viruses, fungi, and parasites, they are all linked by their ability to induce disease conditions in their respective hosts.

The other choices do not fit the definition of a pathogen. For instance, providing nutrients to plants is a characteristic of supportive organisms like certain bacteria or mycorrhizal fungi, which play a beneficial role in plant health but are not pathogens. Similarly, being a parasite implies a relationship where one organism benefits at the expense of another; however, not all pathogens behave this way, as some may affect hosts without being classified strictly as parasites. Finally, beneficial organisms contribute positively to human health, whereas pathogens, by definition, are harmful and lead to disease. Thus, the accurate characterization of a pathogen is its capacity to cause disease, making this the correct choice.