Which type of biological agent consists of living microorganisms?

The correct answer identifies pathogens as types of biological agents consisting of living microorganisms. Pathogens include bacteria, fungi, and some parasites, which can cause disease in their hosts. These microorganisms can replicate and multiply in their environment, leading to infection and adverse health effects.

In contrast, toxins are poisons produced by living organisms but do not consist of living microorganisms themselves; instead, they are chemical byproducts that can cause harm. Viruses, while biological agents, are not classified as living microorganisms in the traditional sense because they require a host cell to replicate and do not exhibit characteristics of life outside of a host. Biohazards encompass a broader category that includes any biological substance that poses a threat to the health of living organisms, which may include pathogens and toxins. Thus, pathogens specifically represent the living microorganisms responsible for infectious diseases.