Multicellular organisms consist of many cells that differentiate to take on specialised functions. For the organisms to function properly, they need transport systems to supply their cells with useful substances (e.g. glucose and oxygen). At the same time, they need to remove waste products that are made in the cells.
These organisms cannot rely on diffusion alone because they are made up of millions of cells. As the size of the organism increases, the surface area to volume ratio decreases. In a larger organism, the reduced surface area means there are fewer places for diffusion to take place. Also, the rate of diffusion may not be fast enough to meet the cell’s requirements. The solution to this is specialised transport systems.
An effective exchange surface has a large surface area and a thin membrane, which provides a short diffusion path. In animals, it is also important to have an efficient blood supply and good ventilation.
The circulatory system in many animals is made up of fluids that can easily pick up and transport substances throughout the body. The circulatory system also includes:
The job of the circulatory system is to transport substances from one area of the body to another.
Plants have transport systems too.