The circulatory system transports oxygen and nutrients to every cell in the body
Single - celled organisms:
Small organisms such as amoeba do not need circulatory systems. They have a large surface area compared with their volume. Dissolved oxygen diffuses from the water they live in into the cell through the membrane. Waste material diffuses out of the cell. Larger animals need a circulatory system because diffusion cannot efficiently transport substances to and from their cells.
Open Systems - Insects:
Insects have open systems. They do not have arteries or veins but…