**3-1 Heat Release due to Growth**

Consider the growth reaction when no significant amount of extracellular product is formed. Under these conditions Eq (2-1) simplifies to

Since nitrogen consumption is usually small compared to the amount of carbon consumed, and that nitrogen does not go through oxidation (while C does !), we can approximate the above as,

Consider heat balance of this reaction using one mole of glucose consumed as the basis.

where (-DH_{C}) and (-DH_{S})
are heat of combustion per gram of cell and per gram of substrate respectively.
Rearranging,

The left hand side is the amount of heat released per gram of substrate consumed and the coefficient of the first term on the right is growth yield. That is,

where Y_{D/S} is "heat yield"
on the basis of substrate consumed. Dividing the above by Y_{X/S }gives

(3-4)

Both Eq (3-1) and (3-2) are useful in determining heat release due to
growth, Y_{D/X }and substrate consumption,
Y_{D/S}.