Question

What do you mean by double anf single circulation?

Answer 1

Single circulation refers to a single cycle of blood moving in the heart.  

During a single cycle blood goes twice in the heart which is known as double circulation .

It is necessary in human beings 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

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It is called a double circulatory system because blood passes through the heart twice per circuit. The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart. The left pump sends the newly oxygenated blood around the body.