I am Groot?

We've all seen the wonder of science fiction that is, Guardians of the Galaxy, right? Well it contains some outstanding scientific achievements, like a cybernetic and overly narcissistic racoon, a vacuum repelling face mask, a black hole grenade, space shuttles capable of time dilation and, what I found most fascinating, a sentient, mobile tree-like organism. That got me thinking, why are there no such life forms on this planet? What stopped plants from developing a CNS + receptors, and becoming as developed as we are? It may be an ambitious aim, but I'm going to try an find out why we are not Groot... so to speak.

Lets start at the beginning, with LUCA (Last Universal Common Ancestor), a bacteria-like organism that lived deep below the earths surface around geothermal hotspots. So it obviously didn't contain chloroplasts for photosynthesis, it in fact used chemiosis, the generation of ATP by the movement of hydrogen ions across a membrane, for its energy. It contained DNA and RNA, with a genetic code composed of 3 base codons, and 80s ribosomes like all eukaryotic life on earth today. Just by looking at the phylogenic tree of life, derived from ribosomal RNA sequence data, you can see that animals and plants only branched from each other relatively recently on the eukaryota arm of the tree. What caused this divide between plant cells and animal cells you may be asking? Well, what could have happened was that during the eukaryotic cell's evolution, it ingested a smaller prokaryotic cell via endocytosis, and the prokaryote just happened to contain the organelles required for photosynthesis. This new combination thrived and became an entirely new brach of our phylogenic history, the plants. They use a complex electron transport chain between 2 photosystems and photolysis to generate NADPH and ATP, which then goes on to produce glucose in a light independent reaction. Whereas animals get their glucose from what they consume, and their ATP is produced via the Krebs cycle and another electron transfer system.

There are definitely other factors that led to this separation, however the key principle to understand here is that plants and animals are fundamentally different organisms, with little overlap in their phenotypes at least. The mechanisms they use to produce ATP , are different enough to warrant such different forms for these organisms, developed through evolution, a topic I will discuss further in my next post...