The terminology used in biological research often includes Latin-derived phrases like in vivo and in vitro. These concepts categorize the environment in which a scientific experiment takes place, defining the study’s conditions. Clarifying the distinction between these terms is necessary for understanding modern scientific research, especially in drug development or cell biology. Determining the classification of common laboratory practices, such as cell culture, helps reveal the goals and limitations of different research models.
Understanding In Vivo and In Vitro
The distinction between in vivo and in vitro depends on whether a study is conducted inside or outside of a living organism. In vivo is a Latin phrase meaning “within the living,” describing experiments performed on a whole, living subject, such as a human, a laboratory mouse, or a plant. These studies are considered the most physiologically relevant because they involve all the complex interactions between cells, tissues, organs, and systems. Examples of in vivo research include clinical trials assessing drug effects or experiments tracking disease progression in an animal model.
In contrast, in vitro translates from Latin as “in glass” and refers to experiments that take place outside of a living organism, typically in a controlled laboratory setting. This research is traditionally performed in glassware, such as test tubes, flasks, or Petri dishes. In vitro methods allow scientists to isolate specific components, like cells or biological molecules, from their natural surroundings for focused analysis. Studying the effect of a toxin on a specific type of cell or testing the antibiotic sensitivity of bacteria are examples of studies conducted in vitro.
The Characteristics of Cell Culture
Cell culture, a foundational tool in molecular sciences, is classified as an in vitro method because it involves growing cells outside their native organism. This process requires isolating cells from a patient or tissue source and maintaining them in a highly controlled, non-living environment. The cells are typically grown in laboratory vessels, like plastic flasks or dishes, often forming a two-dimensional (2D) layer.
The environment is maintained artificially to mimic some conditions within the body. This involves submerging the cells in an artificial nutrient medium, a complex liquid containing growth factors, serum, and hormones. Researchers continuously regulate physical conditions, including temperature, which is often 37°C for mammalian cells. They also control the gas composition, managing levels of oxygen and carbon dioxide. Since the cells are sustained in this artificial system outside the whole organism, cell culture is considered an in vitro practice.
The Importance of the In Vitro Environment
The in vitro nature of cell culture grants researchers a significant advantage: a high degree of control over experimental variables. Scientists can precisely manage the physicochemical environment, including pH, osmotic pressure, and the concentration of nutrients or compounds being tested. This control promotes consistency and reproducibility, meaning experiments can be repeated with similar results.
This controlled environment is useful for foundational investigations, such as studying cell division, disease mechanisms, or the toxicity of pharmaceutical compounds. Researchers can test a specific drug concentration directly on a cell line without the interference of a whole organism’s systemic responses, such as metabolism or immune reactions. The simplicity and scalability of cell culture make it a cost-effective method for high-throughput applications, like initial drug screening. This allows researchers to screen compounds before proceeding to more complex in vivo testing. The ability to observe cellular behavior directly under a microscope also enables detailed analyses impossible within a living body.