If I had a microscope that could see atoms and molecules, how far out would I need to zoom before I could tell I was looking at life?
I’ve heard things like “people are 70% water” but water is not alive.
I’m asking in chemistry because I’m not sure if life at a molecular level is considered biology.
In: Chemistry
This is very difficult to answer, because how do we define life? Would having active cellular processes count as being alive? Would the cell have to perform a full range of life processes for it to be counted as living?
You could watch a sperm cell swimming around, for instance, but although it’s an alive cell it isn’t a living organism.
Zooming in to a cell’s membrane, you could watch proteins such as ion pumps, powered by energy made by the cell in the form of ATP molecules, do their thing. At an atomic level, you could see ions being pumped through, but we could fake that in a lab by artificially supplying ATP and ions. Likewise, we could look at DNA being transcribed or proteins being manufactured within the cell, but we can do that in the lab too using modified cells that aren’t really alive.
I think the smallest thing you could measure that you could undoubtedly say was life would be the smallest living organism, the single-celled [*Nanoarchaeum equitans*](https://en.wikipedia.org/wiki/Nanoarchaeum_equitans) at 400nm, as it’s the smallest thing that can do everything we associate with life (movement, respiration, growth etc.). Even then, it has to live inside a larger single-celled organism as a parasite as it’s missing a lot of normal cellular processes!
I think your question may be more rooted in philosophy than chemistry or biology.
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