Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Pathogens are microorganisms, such as viruses and bacteria, that can cause disease in living organisms. They invade the body and disrupt normal bodily functions, leading to illness.
Bacteria are single-celled microorganisms that can be found almost everywhere. While some bacteria are harmless or even beneficial, others can cause infections and diseases.
Parasites: Parasites are organisms that live on or inside another organism (the host) and rely on it for survival. They harm the host by taking nutrients or causing damage to tissues.