Infectious Disease is defined as a disease caused by the entrance into the body of organisms that then grow and multiply there, often used synonymously with communicable disease. Which choice matches this definition?

• A. A disease caused by toxins produced in the environment
• B. A disease not caused by microorganisms
• C. A disease caused by the entrance into the body of organisms that grow and multiply there
• D. A disease caused by genetic mutations

Answer: (C)

The key idea is that an infectious disease occurs when a microorganism actually enters the body and is able to grow and multiply there, causing illness and sometimes enabling transmission to others. The option that says a disease is caused by the entrance into the body of organisms that grow and multiply there directly describes that process, so it best matches the definition given.

Other possibilities describe mechanisms that aren’t infectious diseases as defined here: toxins produced in the environment cause illness without the pathogen entering and multiplying inside the body; a disease not caused by microorganisms is by definition not infectious; and a disease caused by genetic mutations involves changes in the host’s own genetic material, not an invading organism.