ABSTRACT
Growth of living (viable) cells requires intimate contact of a small quantity of living cells with a liquid solution (medium) containing appropriate levels of nutrients at a suitable pH and temperature. Depending on the morphology of cells under consideration, one needs to consider two different manifestations of cell growth. For unicellular organisms which divide as they grow, an increase in biomass (mass of viable cells) is accompanied by an increase in the number of cells present in the culture (cell-medium suspension). The situation is very different in the case of growth of molds, which are popular organisms for industrial production of a variety of antibiotics. In the case of molds, the length and number of mycelia increase as the growth proceeds. The growing mold therefore increases in size and density (concentration) but not necessarily in numbers. (There isn’t a one-to-one relation between the number of distinct multicellular units and amount of biomass.)
The extent of complexity of the kinetic description to be considered depends on the complexity of the physical situation under consideration and the intended application of the kinetics (fundamental understanding of cellular processes, design and simulation of bioprocesses, optimization and control of bioprocesses). However simple or however complex the kinetic description be, it must incorporate certain key cellular processes, such as cell replication (cell growth), consumption of essential nutrients, synthesis of end products (followed by intracellular accumulation or excretion of these), and cell death/lysis.
