Which of the following is a characteristic of pathogens?

The characteristic that pathogens can cause disease in hosts is critical to understanding their role in public health and ecology. Pathogens include a wide variety of microorganisms, such as bacteria, viruses, fungi, and parasites, that can invade host organisms and cause illness. This pathogenic behavior is what differentiates harmful organisms from non-pathogens or beneficial microbes.

Understanding that pathogens can cause disease is essential for recognizing their impact on human health, agriculture, and the environment. This knowledge underlines the importance of monitoring water quality, as pathogens in surface water can lead to serious health risks for humans and animals.

The other options present characteristics that do not align with the general definition of pathogens. For example, not all pathogens are multicellular; many are unicellular microorganisms. Furthermore, while some microorganisms may be beneficial to human health, pathogens are specifically harmful. Lastly, pathogens do not only reproduce under laboratory conditions; they often reproduce in natural environments, including water, soil, and within host organisms.