So what we were thinking a while ago is that firstly the cell needs to able to make a copy of itself. To do that it has to make proteins, DNA and fatty acids. That’s why this diagram has those things at the peaks. (Proteins also have Agents above them as Agents are just specialist proteins).
Secondly fatty acids act as a storage container. So if you are in a nutrient rich area you fill up on fatty acids and then burn them later in a nutrient poor area. On the transition to multicellular some cells can specialise as fat storage cells and have that as their primary function, allowing the player to add fat stores to their creature.
Very happy to discuss any of this again 
Great work on the process system in general.