A test tube is a common laboratory tool made of glass or plastic, characterized by its cylindrical shape with a rounded, closed bottom and an open top. It is primarily used to hold, mix, or heat small quantities of liquids, chemicals, or biological samples during experiments. Test tubes come in various sizes and materials, including borosilicate glass for heat resistance and plastics like polypropylene for chemical resistance.

In laboratories, test tubes serve multiple purposes such as conducting chemical reactions, growing and culturing microorganisms like bacteria, storing samples, and heating solutions. They are essential for qualitative observations rather than precise measurements and can be sealed with caps or stoppers to prevent contamination. Specialized types include centrifuge tubes for spinning samples and PCR tubes for genetic testing.

Test tubes are favored in scientific research due to their durability, ease of use, and versatility across disciplines including chemistry, biology, and biochemistry. Their transparent nature allows scientists to closely observe reactions and changes during experiments.