Final answer:
Many animals engage in shivering, an involuntary muscular activity, to generate heat when insulation like fur, fat or feathers is insufficient. Shivering efficiently converts ATP energy into heat, helping to maintain body temperature under cold conditions.
Step-by-step explanation:
When insulation fails, many animals resort to shivering, which is a form of involuntary muscular activity that increases heat production. Shivering involves rapid, rhythmic muscle contractions that generate metabolic waste heat, helping the animal to maintain its body temperature. In extreme cold, this reflex is essential for survival in endotherms, as it allows the conversion of energy from ATP into necessary heat.
In addition to shivering, certain animals, particularly mammals, have adaptations such as fur, fat, and feathers to provide insulation. For example, animals like the polar bear or the arctic fox have thick fur that traps a layer of insulating air close to the skin. Furthermore, mammals have a fatty layer known as brown fat that specializes in generating heat. The involuntary action of arrector pili muscles can also increase this insulating effect by causing hair to stand up, although in humans, this primarily results in goose bumps due to our relatively hairless bodies.