[Doctor Stochastic]

So being presented with one cell which is dead and one which is alive, how would you describe the difference?

One is dead. The other is alive. But that isn't the interesting case (although it may be rather difficult to tell whether a cell is dead or alive.)

Living creatures can have dead cells (hair, nails, skin) and dead creatures can have living cells (all cells do not die at the same time when a mammal dies; some may even be kept "alive" indefinitely in a nutrient broth.)

The requirement of restricted environment shouldn't disqualify something from being called living.

[Alamo-Girl]

One is dead. The other is alive. But that isn't the interesting case (although it may be rather difficult to tell whether a cell is dead or alive.)

Living creatures can have dead cells (hair, nails, skin) and dead creatures can have living cells (all cells do not die at the same time when a mammal dies; some may even be kept "alive" indefinitely in a nutrient broth.)

But I'm not asking for anything so grand as whether an entire creature is alive or dead.

Just take two skin cells, one alive, one dead and describe the difference between them.

In my view, that is the first question which must be answered before anyone can seriously approach the "origin of life" question.