Final answer:
Animals respond to the cold by growing more fur, which serves as an insulator, and by using arrector pili muscles that make the hair stand up to trap more air for warmth.
Step-by-step explanation:
Response to a Stimulus in Animals
When the weather gets colder, a physiological response is triggered in animals to grow more fur. This is a biological adaptation mechanism where the fur serves as an insulator, trapping warm air close to the body and conserving heat. The process is controlled by the nervous system responding to the stimulus of cold temperatures. Arrector pili muscles in the skin contract, causing the hair to stand up, which increases the insulating effect by trapping more air. This hair-raising reaction preserves a constant, warm body temperature, which is essential for survival in cold climates.
The growth of thicker fur in animals like polar bears, seals, and the Arctic fox serves as a prime example of this response. Fat layers can also contribute to insulation, helping to conserve heat. However, the loss of significant amounts of body fat can compromise an individual's ability to conserve heat, underscoring the importance of both fur and fat as mechanisms for heat conservation in cold environments.
Humans and the Cold Stimulus
Similarly, humans exhibit a residual response to cold through the contraction of the arrector pili muscles, resulting in what we call "goosebumps." While not as effective due to our relatively hairless bodies, it is a remnant of this heat-conservation response seen in other mammals.