“Carbon’s Metabolic Pathways” by NREL . Carbon goes through numerous metabolic pathways to synthesize compounds needed by the cells. Here’s a representation of two possible pathways. Diatoms store carbon in lipid form or carbohydrate form. The result of the NREL experiments suggests that it might be possible to alter which path the cells use for storage (e.g. more toward lipid synthesis, less to carbohydrate synthesis).