Question

why is it necessary to separate oxygated and deoxygenated blood in mammals and birds​

Answer 1

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It is necessary in mammals and birds to separate oxygenated and de-oxygenated blood because this makes their circulatory system is more efficient and helps in maintaining constant body temperature

Answer 2

As they need to maintain their body temperature (Thermoregulation) so they need a constant supply of energy. They need a good supply of oxygen to facilitate their daily activities hence the separation of oxygenated and deoxygenated blood.