The Alaskan wood frog "Rana sylvatica"

 

The Alaskan wood frog "Rana sylvatica" survives winter by freezing solid, a remarkable adaptation called cryoprotection. 

As temperatures drop, it produces high levels of glucose, acting as a natural antifreeze, which prevents ice crystal formation in cells, protecting them from damage. 

Up to 65% of its body water freezes, halting breathing, heartbeat, blood flow, and brain activity. The frog enters a state of suspended animation, with metabolic processes nearly stopped. 

Ice forms in extracellular spaces, while vital organs remain unfrozen due to glucose. In spring, rising temperatures thaw the frog, and its systems restart—heart, lungs, and brain resume function as if unaffected. 

This ability relies on specialized proteins and glucose metabolism, allowing the frog to endure extreme cold. 

This adaptation fascinates scientists, offering insights into organ preservation and potential medical applications, like cryopreservation, while showcasing nature’s resilience.