In vitro studies refer to experiments that are conducted outside of living organisms, typically in a laboratory setting using cell cultures, isolated tissues, or biochemical assays. These experiments are designed to study the biological processes of cells, tissues, or molecules in a controlled environment.

On the other hand, in vivo studies refer to experiments that are conducted within living organisms, typically in animal models or in human subjects. These experiments are designed to study the biological processes of living organisms in a more complex environment that includes interactions between various systems, such as the immune system, nervous system, and endocrine system.

Both in vitro and in vivo studies are important for understanding the mechanisms of biological processes and for developing new treatments for diseases. In vitro studies are often used to screen potential drug candidates and to investigate the basic mechanisms underlying biological processes. In vivo studies, on the other hand, are used to test the safety and efficacy of drugs and to evaluate their potential side effects in a living organism.