Question

what is the need for seperation of oxygenated and deoxygenated blood from mixing​

Answer 1

Now, yes. It is absolutely necessary to separated oxygenated and deoxygenated blood in mammals and birds. Actually, the evolution came up with the need for energy. With the need for higher activity, came requirement of more energy, and this evolution has made it possible. So now, mixing both the bloods will not only harm the being but will also kill it.

Answer 2

Such separation allows a highly efficient supply of blood. Birds and mammals who have high energy needs use this energy to maintain their body temperature.

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