Difference between simple stirred tank bioreactor and sparged stirred tank bioreactor

Dear Student,
A stirred tank bioreactor is cylindrical with a curved base to facilitate the mixing of the contents in reactor. Stirrer plays a role in mixing and equal oxygen availability throughout, So the difference is - Bubbles increases the surface area in sparged type hence increases transfer of oxygen whereas in simple type there is no presence of oxygen bubbles. 
Regards