Final answer:
Homeostasis is the body's ability to maintain internal stability. In response to cold external temperature, mechanisms like vasoconstriction and shivering help increase body heat.
Step-by-step explanation:
Homeostasis is the body's ability to maintain internal stability despite changes in the external environment. It involves a feedback mechanism that uses negative feedback loops to keep variables within their normal range. In the case of cold external temperature as the stimulus, the body would respond by activating mechanisms to increase body heat and maintain a stable internal temperature. For example, vasoconstriction reduces blood flow to the skin, conserving heat, and shivering generates heat through muscle contraction. These responses help restore body temperature back to the normal range.