premise: Physical entities are distinguished by life.
hypothesis: Life is a characteristic distinguishing physical entities having biological processes , such as signaling and self-sustaining processes , from those that do not , either because such functions have ceased , or because they never had such functions and are classified as inanimate . Cells are sometimes considered the smallest units and `` building blocks '' of life . Death is the permanent termination of all biological functions which sustain an organism , and as such , is the end of its life .