Comment by TeMPOraL

They are not independent. They're specialized. They're machines bred to perform highly specific functions in a very specific environment. They cannot survive outside of it.

Edit: in fact, this "negative space" is probably underappreciated as the force defining the concept of a "living organism" itself. The fact that we can't just swap cells or pieces of cells around, that there is no universal, general-purpose cell that can be a skin cell today, a muscle cell tomorrow, a brain cell next week - is what makes nature be composed of organisms, instead of just being one big soup of cells.