Multicellular organisms are organisms made up of many cells, with groups of 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, there are fewer places for diffusion to take place due to the lower surface area. Also, the rate of diffusion may not be fast enough to meet the cell’s requirements. The solution to this is specialised transport systems.
The effectiveness of an exchange surface is increased by having a large surface area and a thin membrane. This provides a short diffusion path. In animals, it is also important to have an efficient blood supply and good ventilation.
Many animals have a circulatory system that is made up of fluids. They can easily pick up and carry substances around 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.