How does the wood frog survive winters in which up to roughly two-thirds of its body water freezes solid?
- It burrows deep enough underground to stay below the frost line entirely
- It floods its tissues with glucose that acts as a natural antifreeze, protecting its cells as ice forms around them
- It slows its heart and breathing but keeps all of its body water in liquid form
- It produces a waxy skin coating that insulates it from freezing temperatures
Why B? And why not the others?
Correct answer: B. It floods its tissues with glucose that acts as a natural antifreeze, protecting its cells as ice forms around them
When ice crystals begin forming under a wood frog's skin, its liver floods the bloodstream with large amounts of glucose, which concentrates inside its cells and keeps them from freezing and rupturing even as ice spreads through the spaces between cells; its heart and breathing stop completely, and it can remain a frozen block for weeks before thawing back to life in spring. Wood frogs actually hibernate under shallow leaf litter rather than deep underground, which is precisely why they need a freeze-tolerance trick instead of simply escaping the frost line. Some hibernating animals do slow their metabolism dramatically while keeping all their body water liquid, but that is a different survival strategy from tolerating ice formation altogether. No frog is known to produce a wax-like skin coating for insulation against freezing.
Source: USGS & U.S. National Park Service: wood frog freeze tolerance and glucose cryoprotection.