Question

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Answer 1

Warm-blooded animals such as birds and mammals maintain a constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, these animals require more oxygen $\left(O_2\right)$ for more cellular respiration so that they can produce more energy to maintain their body temperature. If the oxygenated and deoxygenated blood mixed together in mammals and birds, the availability of oxygen for cellular respiration would decrease and result in difficulty to maintain the internal body temperature which could be fatal for the organism.

Thus, it is necessary to separate oxygenated and deoxygenated blood in mammals and birds.