Compounds Protect From Freezing

a brown and black frog with gold eyes peek out from under algae in a pond

Biological Strategy

Wood frog

AskNature Team

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Protect From Ice

Freezing temperatures can be difficult for living systems to manage. They can cause ice crystals to form in blood and tissues, which causes damage to cells and ultimately, death. Living systems can’t afford the energy required to melt ice crystals, so instead, many have strategies to prevent crystals from forming in the first place. Many amphibians, plants, and insects have chemicals that act as antifreeze to prevent icy crystal formation. Another challenge ice presents is that it creates a slick surface, requiring friction to traverse. This is why polar bears’ paws have a rough surface that grips ice.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Amphibians

Class Amphibia (“to live a double life”): Frogs, salamanders, toads

Amphibians live a “double life” by being able to survive both on land and in water. Unlike reptiles with dry, scaly skin, amphibians have smooth skin that needs to be kept moist. Many live in the water through development and start life with gills, and then transition to breathing with lungs. They can get even more oxygen through cutaneous respiration, or breathing through their skin. This class represents the first animal group to be able to efficiently walk on land—aided by the well-defined limbs that gave them a “leg up” on their finned competitors.

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Compounds, such as sugar, in the blood of wood frogs protect them from freezing temperatures by affecting how water freezes in the body.

“The North American wood frog (Rana sylvatica), for instance, can survive freezing temperatures for as long as seven months, relying on a natural antifreeze in its blood to protect its organs.” (Morell 2001)

Last Updated August 9, 2017

References

“The accumulation of high levels of low-molecular-weight solutes (polyhydric alcohols, saccharides [e.g., the sugar glucose]) provides cryoprotection to freeze-tolerant animals by minimizing, via colligative [binding] effects, the percentage of body water converted to extracellular ice and the extent of cell volume reduction…[F]reeze-tolerant frogs respond to ice formation in peripheral tissues by synthesizing large amounts of glucose in the liver and rapidly distributing the sugar throughout the body…Proton magnetic resonance imaging of freezing and thawing in whole frogs showed a new adaptive effect of the very high glucose levels in core organs; during thawing, organs such as liver and heart melted first, allowing recovery of their vital functions to begin while the rest of the frog thawed.” (Storey 1997:319)

Journal article

Organic Solutes in Freezing Tolerance

Comparative Biochemistry and Physiology Part A: Physiology | 01/07/1997 | Storey KB

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Reference

“Seminal studies of freeze tolerance in woodland frogs have documented their efficacious system for copiously mobilizing glucose or glycerol in direct response to corporal freezing (Schmid, 1982; Storey and Storey, 1988). Cryoprotectant is chiefly derived from glycogen that accumulates in liver, representing up to 20% of organ mass, during late summer and autumn. Triggered by ice nucleation, its synthesis and export to other tissues proceeds rapidly, with concentrations in blood and core organs ultimately reaching 100–250 mmol l⁻¹. Such levels are readily tolerated by these frogs, but would be deleterious in endotherms. Upon thawing, cryoprotectant is returned to the liver and reconverted to glycogen; reabsorption of glucose in the urinary bladder assists this process and limits the excretory loss of this valuable solute (Costanzo et al., 1997a).” (Costanzo and Lee 2013:1965)

Journal article