What Is the Significance of the Industrial Practice of Waiting

What is the significance of the industrial practice of waiting for cultures to enter the stationary phase of growth before harvest?

A) The cells are at peak metabolic activity.
B) Secondary metabolites are often the desired product, and are only produced in stationary phase.
C) The desired primary metabolites are produced in stationary phase.
D) Potential toxins from log phase growth have been depleted.
E) An optimal combination of primary and secondary metabolites is being produced.