Humans, just like every other living organism on our good, green planet, function properly thanks to our cells. They are the building blocks of life; without them, we wouldn't exist. In order for the cells to operate fairly, they need to be continuously taking in nutrients, such as oxygen and food.
Likewise, the cells need to dispose their wastes: carbon dioxide, any excess of toxins, etc. Since cells are what keep us breathing, moving, and living, it is very important to make sure they function properly and get what they need to work well. Nevertheless, not all of the organisms are exactly the same; and for that reason, there are two types of systems: a simple system and a complex system.
A simple transportation system can be found in any unicellular organism, for instance amoeba (picture on right). Unicellular organisms are made up of only one cell, so their transportation systems are quite basic, since as they do not have lots of cells that have to be nourished. Amoebas, for example, nurture themselves by letting oxygen and other nutrients into the cell and then discharge carbon dioxide and excess wastes out into the atmosphere. This happens with ease since there is less oxygen in the amoebas than in the nearby atmosphere; that is because the oxygen inside the amoebas is continually being respired at the same time as the oxygen outside of it is just floating around. This goes for carbon dioxide as well, except that in this case it goes in the other direction: the amoebas contain more carbon dioxide than the surrounding atmosphere; consequently, the carbon dioxide slides out of the cell, hence getting rid of any wastes the cell might produce.
Complex transportation systems are a little more complicated because they consist of many cells, and therefore require a much more elaborate way to meet all of those cells’ needs. That means blood is needed to transport all of the required nutrients the cells need. Blood requires a heart to pump it, lungs to give...