Heat flux and the growth reaction

The validity of the constructed growth reaction can be tested by the enthalpy balance method (see Sections 2 and 5.2.4). The metabolism of animal cells is much more complex than that of microbes but it has been found that in practice the components of the growth reaction can be simplified sufficiently to make the exercise a feasible one for cells grown in a defined medium without serum [44]. Although there are still many nutrients without this complex additive, it has been shown that the micronutrients can be neglected and that, for enthalpy balance studies, it is justifiable to ignore the amino acids [105] because the 

It means that the metabolic activity of the cell determines the stoichiometry of the growth equation and a particular set of stoichiometric coefficients for this equation corresponds to a value of the metabolic activity for the same amount of viable cell mass. Thus, for Equation (13), the growth reaction is characterised by its set of stoichiometric coefficients [105], that is. 

Looking at Equation (14) in the light of Equation (15), it is explicit that the cellular metabolic requirement can be determined by measuring the metabolic flux, specifically represented by the heat flux variable [105]. Since the metabolic flux varies with time in culture, the stoichiometry expressed by Equation (14) must change to reflect it. If the variable is measured for the culture on-line and 

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