A test tube is a small, cylindrical glass or plastic container used in laboratories for holding, mixing, or heating liquids. They are often used in scientific experiments to observe chemical reactions or to store samples. Test tubes come in various sizes and are usually open at the top, making it easy to add or remove substances. In addition to their use in science, test tubes are also popular in educational settings, where students learn about basic chemistry concepts. They can be found in many science labs, and are essential tools for scientists and researchers working in fields like biology and chemistry.