What do you understand by double circulation? Explain the transport and exchange of oxygen and carbon dioxide with the help of schematic representation (diagram).

Hint: The human circulatory system is a double circulatory system and is composed of the heart and a system of blood vessels (arteries, veins, and capillaries). In this process, the blood passes two times through the heart in one cycle.

Complete answer:
The circulatory system of humans (higher vertebrates) is divided into two separate systems of circuits, the systemic circuit, and the pulmonary circuit. Each of these systems consists of a similar sequence of blood vessels. The aorta carries oxygenated blood to all parts of the body, and the superior and inferior vena cava brings deoxygenated blood from the entire body and drains into the heart this process is known as systemic circulation.
The circulation of oxygenated blood starts from the left auricle followed by the left ventricle. It distributes nutrients and oxygen to body parts. Blood is pumped out of the heart into arterioles through arteries (blood vessels which are muscular tubes lined by smooth tissue) of decreasing size, which merge before reaching the sites of exchange with the capillaries (tiny blood vessels connecting arteries to veins). Blood leaving the capillaries is gathered into venules and then veins before returning to the heart. Also, the left side (left auricle and left ventricle) provides pressure to propel blood to the entire body.
The pulmonary circuit, the right side of the heart, carries deoxygenated blood from the heart to the lungs for gas exchange with the atmosphere and returns oxygenated blood to the left atrium and ventricle of the heart. Both the systems, i.e systemic circulation, and pulmonary circulation are readily paired and contrasted with each other.

Note: Capillaries are very tiny blood vessels and they help to connect arteries and veins. The primary function is to facilitate the exchange of certain elements between your blood and tissues.