Bacteria can continue like nothing happened after being exposed to low temperatures why doesn't this happen to humans as well? Why can't our metabolic machinery continue as normal?

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    $\begingroup$ I think a better question would be something along the lines of "Do human cell lines tolerate cold temperatures?" The question as is is quite trivial - we are multicellular organs that rely on systemic functional integrity, whereas generally bacteria are single-cellular organisms. It's comparing apples and oranges at the minute. I think there is an interesting question in there, but major edits would be required. $\endgroup$ – James May 14 '16 at 4:57
  • $\begingroup$ @James Why would this be a homework question? $\endgroup$ – SaudiBombsYemen May 16 '16 at 15:20

Let's look at what happens when a single cell within a cell wall freezes. We end up with a little drop of ice, within which are encased all the cellular structures. Thaw this ice, and all is well - provided neither freezing nor thawing happen too rapidly.
Now take what happens in a human being.
First, the blood in the extremities gets colder, and cools the interior somewhat. But we have mechanisms to conserve heat in the core, at least for a little while. This doesn't help the extremities much. If the blood freezes there, we get frostbite - the tissues die for lack of blood supply. Fingers and toes and the end of the nose, and other extremities, are compromised.
Now let the core temperature drop. Below a certain temperature, conduction in the heart slows and eventually stops. This is fatal.
There are many other effects, all of them related to the relative vulnerability of different tissues to cold. Freezing is generally bad for animal cells, which will rupture because of the mechanical effects of the expansion of water as it forms ice. Frozen body fluids can't do their jobs. Frozen nerves can't conduct impulses, so muscles won't contract once their temperature drops below the shivering point. And so on.

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    $\begingroup$ But why can't our cells resume normal activity after being frozen? Once that blood reaches the cells again why can't it function normally? What structures in our body or cells prohibits this from happening? $\endgroup$ – SaudiBombsYemen May 14 '16 at 11:41
  • $\begingroup$ I edited to make clear that ice formation will rupture the cells. If the heart has stopped, the body dies. And when the formerly frozen body thaws, the cells do function normally by decaying, which is normal function for dead cells. $\endgroup$ – frank May 14 '16 at 16:28

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