Adding acid or alkali in a bioprocess is related to which control?

Correct answer: pH control

The governing concept is pH regulation in a biological culture. Acids release hydrogen ions and generally lower pH, whereas alkalis neutralize acidity and generally raise pH. During fermentation, microbial metabolism can change the acidity of the medium, so sensors and a control system may add acid or base to keep pH within the range required for growth, enzyme activity and product formation. Option B is therefore correct. Temperature control uses heating or cooling, pressure control changes vessel pressure, and light control concerns illumination; none is identified by adding acid or alkali. The addition must be gradual and monitored because an excessive dose can create local pH shock or harm cells.