Why is an open circulatory system less efficient than a closed circulatory system?

Answer 1

In an open circulatory system, a heart pumps blood all over without rhyme or reason. Blood can't be controlled, it all just moves about as it wants. oxygenated and deoxygenated blood mixes. This is slow and inefficient. In a closed system, blood is contained which allows for control and separation of deoxygenated and oxygenated blood.