What is the simplest entity that would be considered "conscious"? Generally, we think of humans as having a (relatively) advanced level of consciousness, but we don't think of simple molecules as having any sort of mental capacity at all. So where in between does the phenomenon of consciousness arise?

Update: I have chosen G.Tononi's definition: the quantity of consciousness corresponds to the amount of integrated information generated by a complex of elements
As strange as it may seem the answer to the question is that when two braincells or neurons work together a small conciousness is created. We have billions of neurons so that conciousness would be rather small. Of course, this depends on the definition of counciousness and neurons.