Correct Option: C

High density culture is dependent upon high levels of available dissolved oxygen at times of maximum growth (using cascades of process parameter such as stirrer speed, gas flow and oxygen supplementation) or control of feed to match the quantity of substrate which is already present in the bulk culture. In a microbial culture, microbial metabolism is controlled on the basis of respiratory quotient (R.Q.). If, however, there occurs a sudden increase in the R.Q. of the microbial culture, it implies that rate of fermentation is increasing more than that of the rate of respiration.