I remember there is this lifeform that maintains a symbiosis, in the sense that it's a transparent lifeform, and this particular algea grows within it's insides.
Between the two, light makes the algea grow, and the lifeform feeds from the algea, they can coexist.
The cellular structure of plants in comparison to that of animals is different, not just due to one acting on photosynthesis while the other works on other chemical reactions without need of light.
You can guess that planet RNA has a far different pattern to that of a human, in fact it's a less complicated pattern and more versitile.
I did previously wonder about creating a creature from fungus. (Yes, a Quorn Creature) The reason for this is Fungi can "destroy and retrograde" cellular structures, which basically means it can evolve(mutate) a derivative from the original.
In fact if anyone else actually has read "Neuromancer" by William Gibson, they will note that Gibson creates a piece in the world for replacing nerve tissues, in which case a mycosynthetic tissue was used.
(Note:
In Cybernetics, a Myco-electric process is what can be used to control a cybernetic limb, that's acting as a replacement for an amputation.
http://www.biol.tsukuba.ac.jp/~macer/EJ116/ej116c.htm
)