Hierarchy of Consciousness

A topic worth exploring...

I was thinking about the increasing complexity of biological systems and how these systems are related to consciousness.
My primary assumption is that panpsychism is correct in saying that everything in the universe is conscious to some degree. Starting from the tiniest sub-atomic particles to the vastness of galaxies and beyond. This, coupled with the fact that conscious individual agents bond together in more complex systems, giving rise to a consciousness that is more than just the sum of its parts, brings us to a very interesting deductions.

In simple terms, take cells for example. Cells have their own individuality. They interact with their surroundings, they reproduce, they have their own goals and purpose. When they bond together to form an organ, they all work together to fill a higher purpose. The organ itself acquires new faculties and tools to interact with their surroundings. This new entity thus seems to be more than just a mere accumulation of cells. 

If we go one step further, we arrive at the human being, who is a collection of organs and parts. Yet, most will agree that we are more than that. There is a consciousness that oversees the function of all the different parts. Again, there is a new identity, there are new tools to interact with the world and new purposes.

But what if we take this a step further? What if we are all part of a bigger "organism", resulting in a higher order of complexity and consciousness? 
If this drive to unite individual agents into more and more complex systems can be seen throughout nature, does it make sense to you that it would stop at the human being, as if we were the glorious culmination of a very long evolutionary process?
Or would it make more sense to identify the human being as just another step of this process? 

In short....
Lower systems are transcended and included in higher systems, resulting in a consciousness that is more than the sum of its parts.

What about consciousness?
However you may define consciousness, I think we can agree that human beings are conscious. 
Who or what else is conscious in your opinion? Lots of people believe that mammals with big brains are also conscious (dolphins, primates), but also dogs, pigs, horses etc. 
Then it gets more difficult. Can we attribute consciousness to "lower" life forms, such as birds, bugs or worms? Why or why not? 
What about plants? Are they conscious?
How far down the scale are you willing to attribute consciousness? 
What about cells? Atoms? Subatomic particles?