A1 - Prairie dog
B2 - Wood frog
C3 - Snowy owl
D4 - Arctic hare
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Answer: Wood frogs have the uncanny ability to survive being frozen solid. In order to survive the cold, they have a unique adaptation: they are able to freeze solid without damaging their cells. Sugar acts as a natural antifreeze in their bodies, allowing them to spend the winter in this frogcicle state and regain normal function in the spring. At the first sign of ice in late fall or early winter, the frog freezes solid as a rock. When warmer spring temperatures trigger the frog to thaw, its heart and brain thaw first, followed by its body, all in perfect synchrony. Within 10 hours, the frog is fully functional.
During winter, the wood frog (Rana sylvatica) can be easily mistaken for a dead animal: it is frozen motionless, including the brain and the eye lens, and has no detectable heartbeat or breathing activities. However, the frogs survive this state and thaw back to life in spring; the cycle repeats for several years during the frog's lifetime.
This became possible thanks to several adaptations. First, special nucleating proteins remove the majority of the water from the frog's cells, so the ice, when formed, could not tear them apart. Then the frog's liver produces glucose, which fills the cells with the fluid that is resistant to being fully frozen.
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