MRS. C GREN (Movement, Respiration, Sensitivity, Cells, Growth, Reproduction, Excretion and Nutrition.) is an acronym I learnt at school to categorise things as living or non-living. If something does all of these it is considered alive.
My teacher told me cells are included to categorise fire as non living (as fire fulfills all other requirements).
Even after finishing school I am still annoyed by this requirement. Cells are the basic unit of life. So cells need to be alive to be cells, but you also need to have cells to be alive, in other words you need to be alive to be alive, not very useful for determining if things are living or not.
So I propose an amendment, remove C and add E - for ability to Evolve. Fire cannot evolve, but I see evolution as an essential requirement for all forms of life.
Much more elegant.
Also as a bonus, MRS. GREEN is a nicer acronym and I think its easier to remember.
Were you taught a better acronym? Or perhaps do you have an even more elegant idea?
MRS GREEN would still exclude viruses as being alive. As viruses can neither respirate nor reproduce without a host cell and they can also not grow.
I'm weird and think a virus in a system of virus + host cell, is a part of the living cell, even if its a detrimental self-serving part.