To help you figure out what the blood might look like, sometimes it is easier if we know what it needs to do. Sort of working backwards. In this analogy we will try to see how the blood carries out its function.

You might think of the blood as a system for delivering materials, much like UPS or Federal Express. If the blood were like a delivery system, what might it need?

If you had a number of these traveling through the circulatory system constantly, what might that look like?

What would they carry?

Where do they travel? Why?