system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What keeps blood "alive" after we donate it?
gpt
A part of you body that's separated from you like blood, or a severed limb, doesn't simply die instantly. All the cells that don't suffer some kind of direct damage simply keep on doing their jobs like normal until they run out of sugars, oxygen, or simply die off through their normal processes. If the cells are no longer connected to you, the first thing they're likely to run out of is oxygen. However, they only use up their oxygen when they're working - when they use energy to perform slcell functions. That's usually all the time, but if the cell is brought to a very low temperature safely (there are special techniques to make that happen), the cell's functions slow down and it doesn't use energy - and oxygen - as fast. That means the cells are still alive when they get put into another person.