Air bubbles are sparged into bioreactor tanks. The role of these bubb…

The correct answer is Option (4) → Increase the area for oxygen transfer

In a sparged stirred-tank bioreactor sterile air is blown in as many small bubbles. Their large total surface lets more oxygen pass into the culture.

Option (1) Remove the foam — Incorrect. Foam is handled by the foam control system; bubbles in fact add to foam.

Option (2) Mix air with the medium — Incorrect. Air does enter the medium, but the purpose of many small bubbles is a larger oxygen transfer area.

Option (3) Mix all the contents properly — Incorrect. Mixing is done mainly by the stirrer, which gives even mixing and oxygen availability throughout the bioreactor. The air bubbles are a way of supplying oxygen, not the main mixing device.

Option (4) Increase the area for oxygen transfer — Correct. Blowing the air in as many small bubbles gives a larger surface area for oxygen transfer, so more oxygen passes into the medium and reaches the growing cells.

NCERT Extract:
Obtaining the Foreign Gene Product – “… A stirred-tank reactor is usually cylindrical or with a curved base to facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor. Alternatively air can be bubbled through the reactor. If you look at the figure closely you will see that the bioreactor has an agitator system, an oxygen delivery system and a foam control system, a temperature control system, pH control system and sampling ports so that small volumes of the culture can be withdrawn periodically.”