Final answer:
The term that describes a disease-causing microorganism is D) pathogen. Pathogens can be microorganisms like bacteria and viruses that lead to infections and diseases which may be communicable between individuals.
Step-by-step explanation:
The correct term used to describe a disease-causing microorganism is pathogen. A pathogen is any agent, particularly a microorganism such as a bacterium or virus, that causes disease. These organisms can lead to infections by successfully colonizing hosts and may result in signs and symptoms, which represent a deviation from normal health.
According to the germ theory of disease, diseases are caused by microorganisms, also known as germs, which are too small to see without magnification. Human pathogens include but are not limited to bacteria, viruses, fungi, protists, helminths, and prions. Antibiotics can treat most diseases caused by bacteria, while antiviral drugs are used to address infections caused by viruses. Infectious diseases can be communicable, meaning they can spread between individuals, and pathogens can be spread through various means, such as person-to-person contact, vectors, or environments.