Final answer:
The shape of a polar bear, being large and round, helps them retain heat and survive in cold Arctic conditions thanks to adaptations such as thick fur and a dense layer of fat, also known as blubber.
Step-by-step explanation:
The large and rotund shape of a polar bear is an adaptation to their cold environment. This body shape conforms to the need for conserving heat and maintaining a stable internal temperature. Polar bears generate heat metabolically and reduce heat loss through their thick fur and a layer of fat beneath their skin. These adaptations are crucial for polar bears to survive in their Arctic ecosystem. The white color of their fur acts as camouflage in the snow and ice, further protecting these top predators. When food is plenty during the summer, polar bears convert excess food into fat, which they can later utilize during periods of scarcity in the winter. The layer of fat, known as blubber, is also found in other animals such as whales and penguins, helping them retain their body heat.