Baby It's Cold Outside
Biologists state that unicellular cells freeze at a swifter rate than multicellular organisms. These scientists have pinpointed the lowest temperature at which simple life can live and grow. When temperatures dip below -20°C, single-celled organisms dehydrate, sending them into a vitrified -- glass-like -- state during which they are unable to complete their life cycle. Researchers hypothesize that, since the organisms cannot reproduce below this temperature, -20°C is the lowest temperature limit for life on Earth.
I read in a recent study that in order to test this theory, scientists placed single-celled organisms in a watery medium, and lowered the temperature. As the temperature fell, the medium started to turn into ice and as the ice crystals grew, the water inside the organisms seeped out to form more ice. This left the cells first dehydrated, and then vitrified. Once a cell has vitrified, scientists no longer consider it living as it cannot reproduce, but cells can be brought back to life when temperatures rise again. This vitrification phase is similar to the state plant seeds enter when they dry out. What is interesting is that once a cell is vitrified it can continue to survive right down to incredibly low temperatures. It just can't do much until it warms up.
More complex organisms are able to survive at lower temperatures because they are able to control the medium the cells sit in to some extent. For example, the research study revealed that animals, trees and insects have the ability to control the fluid that surrounds their internal cells. In a human's case its blood and lymph. In a complicated organism the cells sit in an environment that the organism can control. Free-living organisms don't have this; if ice forms in the environment they are subject to all the stresses that implies. And if a free-living cell cools too quickly it would be unable to dehydrate and vitrify; instead it would freeze and wouldn't survive.
These freezing conditions explain why preserving food using deep freezing works. Most fridge freezers operate at a temperature of nearly -20°C. At this level of temperature bacteria and molds are unable to multiply and spoil food.