There are a variety of answers to this question, but no definite way to determine which is right or wrong. Indeed, as Hartmann and Miller point out, methods of attempting to define llife have evolved to an understanding of life as a series of prcesses, rather than life as a condition or an instant result of exposure to a vital force or earlier definitions. In my opinion, there are certain qualities or characteristics necessary to categorize an organism as alive. One characteristic is the ability to reproduce. This is commonly recognized as an essential component of what we define as life.
Reproduction is indicative of a desire within an organism or set of organisms to continue itself.
Through reproduction, obviously, the parents are able to continue living through their offspring, even after their own lives have ended. This is true especially in terms of the genetic makeup inherited from parents. Another characteristic is the idea of a living thing as something that takes in material and processes it before eliminating the waste it produces. This is a helpful definition of life as it illustrates the processional nature of the system of life. Living organisms find it imperative to interact with their surrounding environments precisely through such processes as eating, drinking, producing chemicals, growing and eliminating wastes.