Biomass concentration
= Biomass concentration
{title2=$x$}
The <biomass concentration> is the mass of biological material per unit culture volume; here it is measured as dry cell mass in $\mathrm{g}\,\mathrm{L}^{-1}$. A <biomass concentration> differs from a cell count per unit volume because cell sizes can change. In the ideal <chemostat>, biomass leaves the vessel at rate $Qx$, giving a removal term $-Dx$ in the <ordinary differential equation> for $x$.