Final answer:
In microbiology, growth refers to an increase in the number of microbial cells, particularly during the log phase of the growth curve. It is typically measured during the production of microbial mass or secondary metabolites.
Step-by-step explanation:
In microbiology, the term growth usually refers to an increase in the number of microbial cells. This growth is evident during the log phase of the microbial growth curve, where cell numbers increase exponentially. The definition of growth can vary among different organisms; for multicellular organisms like humans, growth can include increases in cell number, increases in the amount of non-cellular materials, and limited increases in cell size. However, for microorganisms, particularly bacteria, growth typically pertains to the increase in cell numbers through processes like binary fission.
Microbial mass production often relies on maintaining cultures in the log phase, while the production of secondary metabolites, such as antibiotics, might be optimized during the stationary phase when the growth rate has stabilized.
In the context of the options provided, an increase in the number of microbial cells, which is choice 'a', is the closest definition of growth in microbiology.