2.52 understand the need for a transport system in multicellular organisms

Why do multicellular organisms need transport systems?
-cells in all living organisms need substances (such as water, minerals, sugars) to live. They also need to get rid of substances.
-although unicellular organisms can rely on diffusion (refer to 2.51), it would be too slow in multicellular organisms as they have a smaller surface area to volume ratio. For this reason, multicellular organisms rely on transport systems.

Common features of transport systems:
1. Tubes/vessels
   -carries materials from 1 part to another.
2. Close contact with cells
   -so substances can be exchanged easily in and out of cell.
3. Many have pumps
   -In humans it is the heart, which ensures constant circulation.
   -Plants don't have hearts, instead they have xylem and phloem.