Which term best fits the definition: The presence and activity of disease-causing organisms in the body and the body's response?

• A. Infection
• B. Immunity
• C. Aids
• D. Chemotherapy

Answer: (A)

The concept being tested is infection. It describes both the presence and activity of disease-causing organisms in the body and the body’s response to that invasion. When pathogens such as bacteria, viruses, fungi, or parasites infiltrate tissues, they multiply and cause damage, which then triggers the immune system to respond—fever, inflammation, and immune cell activation are all part of that host response. Immunity, by contrast, is the body’s defense against infection, not the ongoing presence of pathogens. AIDS is a specific disease caused by HIV that compromises the immune system, and chemotherapy is a treatment used for cancer (and sometimes infections) rather than the definition described.