Multicellular Organisms
- Multicellular organisms, like humans, have bodies made up of more than one cell
- The bodies of these organisms contain many layers of cells, meaning that the distance between the surface of the organism to its centre is relatively long and the diffusion distance is too great to rely on diffusion alone
- Diffusion to all of the cells would take far too long
- Diffusion cannot occur at a sufficient rate to meet the needs of the organism, so larger organisms usually have transport systems
- The transport system in animals is the circulatory system which carries the necessary substances around the body in the blood
- The transport system in plants is the vascular system:
- The xylem moves water and mineral ions from roots to shoots
- The phloem moves sugars and amino acids to where they are needed in the plant
Humans and some plants have specialised transport systems
