Final answer:
Brown-fat mitochondria uncouple oxidative phosphorylation to produce heat.
Step-by-step explanation:
C) heat. Brown adipose tissue (BAT), or brown fat, contains a high density of mitochondria with a unique protein called uncoupling protein 1 (UCP1). Unlike in most tissues where mitochondria generate ATP through oxidative phosphorylation, in brown-fat mitochondria, UCP1 allows protons to re-enter the mitochondrial matrix without passing through ATP synthase. This uncoupling of the electron transport chain from ATP synthesis leads to the generation of heat instead of ATP. Brown fat is especially important for non-shivering thermogenesis, a process that helps in maintaining body temperature, particularly in newborns and during cold exposure.