Diffusion

Particle movement 
In high, low concentrations
In and out of cells 

To Do or Not To Do

Afferent in to

The Central Nervous System

Efferent back out

Leukocytes

It will protect you
There are different types of cells
They are colorless 

red blood cells

In everybody
It contains hemoglobin
Little red blood cell

Which Blood Type am I ?

I'm universal 
I produced antibodies 
But not antigen