Explain why having only one ventricle makes the circulatory system less efficient than having two ventricles.

A double-circulatory system compromising two ventricles will be more efficient than with a single ventricle.

Explanation:

When there are two ventricles, they can receive impure deoxygenated and pure oxygenated blood separately.

The human heart is separated into four chambers. The right and left side are separated by the septum. The right ventricle collects deoxygenated blood from right atrium. This deoxygenated blood is pumped via the pulmonary artery to the lungs  for reoxygenation. This part of circulation is pulmonary circulation.

The left ventricle receives oxygenated blood from the left atrium and pumps it to all parts of the body through the aorta. This part of circulation is systemic circulation.

Hence to efficiently perform both systemic and pulmonary circulation, two ventricles are important.

Some animals like frogs have one ventricle and their circulatory system is less efficient.