Qui's first organisms were little more than simple strands of DNA surrounded by thin membranes. The membranes surrounding these primitive organisms allowed necessary compounds from the environment in and conducted waste products out.
These organisms eventually gained the ability to convert energy from Qui's sun into the chemical energy required for cell maintenance and growth.
A meteor collided with Qui, bringing with it (among other things) a class of organisms very similar in size and shape to those found in Qui's oceans, but with one very significant difference - the ability to engulf and "digest" food particles, including the native photosynthetic organisms. The invaders quickly spread throughout Qui's oceans.
Balance was restored as Qui's native organisms eventually developed techniques to deal with these foreign invaders, including avoidance mechanisms and chemical defenses.