Final answer:
White adipose tissue is mainly for lipid storage and insulation, while brown adipose tissue, characterized by an abundance of mitochondria, is thermogenic, generating heat instead of ATP when metabolizing fats.
Step-by-step explanation:
The main feature that distinguishes white from brown adipose tissue is its content of mitochondria and associated capacity for thermogenesis. Brown adipose tissue contains a high number of mitochondria, which imparts a reddish-brown color to the tissue. These mitochondria are responsible for the tissue's ability to oxidize fatty acids and generate heat, a process aided by a protein known as thermogenin that uncouples oxidative phosphorylation, leading to less ATP production but more heat generation. In contrast, white adipose tissue stores lipids and provides insulation but is less involved in heat production.
White adipose tissue appears yellow due to carotene and related pigments from plant food and is most abundant in the body, often providing cushioning and protection to organs.
Both types of adipose tissue are highly vascularized, but it is the abundance of mitochondria that really sets brown adipose tissue apart from white adipose tissue, which has fewer mitochondria.