Paper 3 · June 2017 · aeroponics and fermenter design
The air supplied to a fermenter must be sterile because unsterilised air would
Acool the culture below the temperature that the chosen organism needs in order to grow.
Bdissolve too slowly to meet the oxygen demand of the culture.
Craise the pressure inside the vessel above its safe working limit.
Dcarry in microorganisms that compete with the culture and spoil the product.
Explanation
A fermenter holds a single chosen organism in a rich medium at a favourable temperature, which is equally favourable to any contaminant that gets in. Airborne bacteria and fungal spores would multiply alongside the culture, consume the substrate and leave a product that is impure or worthless. Filtering the air removes them.
Derived from ZIMSEC Biology Paper 3, Jun 2017, Q11