How do you know if a unknown substance is dead or alive?

To determine if an unknown substance is alive or dead, scientists typically look for key characteristics of life, such as responsiveness to stimuli, growth, reproduction, metabolism, and cellular organization. If the substance shows signs of metabolic activity, such as consuming nutrients or producing waste, it is likely alive. Additionally, microscopic examination can reveal cellular structures and activity that are indicative of life. In contrast, a lack of these characteristics suggests the substance is dead.