Final answer:
Brown fat in mammals functions primarily for thermoregulation by generating heat through a specialized form of cellular respiration with high mitochondria density, crucial for maintaining body temperature in newborns and in adults in cold climates.
Step-by-step explanation:
The major function of brown fat in mammals is thermoregulation, particularly in generating heat. Brown fat contains a high density of mitochondria, which are specialized to perform cellular respiration producing less ATP and more heat than typical cellular respiration. This process is vital to help newborns maintain body temperature, as their bodies lose more heat per unit mass due to a larger surface area to mass ratio. In adults, the presence of brown fat is rarer but can be found in those living in cold climates to help maintain core temperature.
Brown fat works by having proteins within the mitochondrial inner membrane that allow protons (H+) to return to the mitochondrial matrix without producing ATP, which results in the release of energy as heat. This breakdown of brown fat is an automatic response to cold exposure, which is crucial for heat regulation in newborns.
Mammals conserve or dissipate heat in various ways, such as through insulation provided by fur, feathers, or fat. Brown fat plays a key role in this system by providing an efficient mechanism for heat generation.