Polar bears have composite internal lungs for gas exchange of O2 and CO2 as they also decrease water loss. Closely attached with a closed double transport system as they transfer oxygen from the lungs and remove CO2 from the cells.

Polar bears have a closed circulatory system, just like other mammals. A closed circulatory system is when their blood never leaves their arteries, veins, and capillaries.

Their digestive system absorbs about 84% of its protein and 97% of the fat it consumes. At least 4.4 pounds of fat is needed per day to survive in the Arctic, and takes 20 hours to digest completely. Like humans, it comes out the other end as feces.

Out of all bear species, Polar bears are the most carnivorous because of their large body sizes that metabolize fat more efficiently than protein that causes them to need an energy-rich diet. They feed primarily on ringed seals, but their diet also consists of bearded seals, harp seals, hooded seals, harbor seals, birds, fish, and vegetation (such as kelp) when food is scarce.  They occasionally take on bigger prey, such as walrus, narwhal, whale carcasses, reindeer, and beluga.

The Polar bears most common prey are seals. The Polar bear waits on the seal to come to the surface of sea ice to breathe, where they then bite/grab the seal and pull it onto land to feed.

The Polar bears structural adaptations includes thick layers of fat and fur. This provides insulation against the cold. A small surface area to volume ratio is to minimize heat loss. A greasy thick coat that sheds water after swimming is to help reduce heat loss.

Fur even grows on the bottom of the Polar bears paws to protect them against the cold surfaces of the Arctic ground and provides good grip on the ice.

Like humans, polar bears run and walk. They have a plantigrade stance, which means they walk on the souls of their feet with their heels touching the ground first. Generally, a Polar bear will walk with a steady, lumbering gate. Like other bears, they can also stand on two feet and walk upright, but only for short walking distances.

A Polar bear is endothermic, which means it can maintain a constant body temperature independent of the environment.

A dominant male Polar bear may succeed in mating with several females in a season. Once paired, the male and female stick together for a week or more. Females are induced ovulators.

Male Polar bears actively seek mating partners in late spring and early summer. These males seek out females by following their scent. Two males may fight over a female. Whichever bear wins, wins the female over and they stay together for about a week or so.