The system which helps in the transportation of various useful substances in the body of living system is known as transportation system or circulatory system.
It generally consists of a heart, blood vessels, blood plasma, blood, blood cells and the lymphatic system.
The circulatory system transports oxygen to the cells for respiration, takes carbon dioxide from the cells and transports it to lungs, transports impure blood to kidneys for purification, transports excretory materials, transports various hormones, etc.
Transportation of all these substances is essential for sustaining the life of the living organism. In this way, the transportation system helps the living organisms by sustaining their life.