Firstly, to design submodel 1, an ODE model was written and simulated for the growth of the bacterial volume depending on a constant growth rate. Here, it was assumed that the concentration of the nutrient does not influence bacterial growth.
Next, the ODE model was modified to take into account the effect the concentration of nutrient inside the bacteria has on the growth rate. This was achieved by using the Hill Function. The Hill function models the cooperativity between a ligand and a macromolecule. So in this case, it links the concentration of nutrients and growth together.
In the final part of step 1, it was assumed that the internal concentration of nutrients (i.e. the nutrient concentration inside the bacteria) varies with time in a way illustrated by a piecewise function. This resulted in a new ODE model.