Plasma and internal membranes
At the moment we don't have a description of membranes.
We removed the membrane synthesis from CWS module since it describes only CW and not peripheral biomass anymore. The internal compartments grow in a constant ratio to the overall cell volume, here, no membrane description is needed or can't be included easily. Nevertheless, we need a lipid sink in metabolism. We should start with the caluclations @veraschue did for the lipid metabolism model (Schützhold et al., 2016).