“In vivo” is a Latin term that means “within the living”. It is used in biology to refer to processes, reactions, or phenomena happening within a living organism. When you’re talking about “cells in vivo”, you’re referring to cells as they exist and function within a living organism.

Studying cells in vivo is crucial because it allows for observation of cellular behavior, processes, and interactions in a natural, physiological context. Cells in a living organism interact with a variety of other cells, extracellular molecules, and physical forces that can significantly impact their behavior. These conditions are often difficult, if not impossible, to replicate accurately in vitro (in a lab dish or test tube).

In the context of research, in vivo studies can involve a wide variety of techniques, from microscopy for observing cells in live animals (like zebrafish or mice), to genetic manipulation techniques for studying the role of specific genes in living organisms.

However, in vivo studies also present significant challenges, particularly in terms of accessibility, ethical considerations (especially in the case of human subjects), and technical difficulties in observing and manipulating cells within a complex living organism.

Overall, while in vitro studies allow for controlled and detailed investigation of cellular mechanisms, in vivo studies are crucial for understanding how these mechanisms function in the context of a whole, living organism.