What term describes an examination done in a living organism as opposed to in vitro?

The term that describes an examination or experiment conducted within a living organism is "in vivo." This Latin phrase translates to "within the living," indicating that the study or observation occurs inside a living biological system, such as an animal or human body. In vivo studies are crucial for understanding how various factors interact in a natural biological environment, allowing researchers to gain insights about physiological processes, disease mechanisms, and therapeutic effects.

The other terms, while related to methods of study, pertain to different contexts. "Ex vivo" refers to studies or experiments conducted on tissues or cells taken from a living organism but not in the organism itself. "In vitro" describes processes performed outside of a living organism, typically in a controlled laboratory setting, such as in test tubes or petri dishes. "In situ" means "in its original place," often used to describe observations or interventions that occur in the natural location within the organism or environment, such as a tumor at its site of origin.

Understanding these distinctions is vital for accurate communication in medical and scientific contexts, particularly in research and clinical practice. Thus, "in vivo" is the correct term when referring to examinations conducted within a living organism.