In aerobic and facultative cultures, what is the typical effect of low dissolved oxygen (DO) concentrations on overall biomass yield (g cells per g substrate)?

Introduction:
Dissolved oxygen is often the primary electron acceptor in aerobic bioprocesses. Its availability directly impacts the balance between respiration (energy-efficient) and overflow pathways (less efficient), which in turn determines how much substrate is channeled to cell mass versus by-products.

Given Data / Assumptions:

• Organisms can respire aerobically when DO is sufficient.
• Low DO forces metabolism toward less efficient pathways.
• Yield Y_x/s is defined as mass of biomass formed per mass of substrate consumed.

Concept / Approach:
When DO is low, cells experience oxygen limitation, reducing ATP generation per mole of substrate. More substrate is oxidized incompletely or diverted to overflow metabolites, lowering biomass yield. Conversely, well-aerated conditions maximize respiratory ATP and support higher yields.

Step-by-Step Solution:

Verification / Alternative check:
Oxygen-limited chemostat data show decreased Y_x/s and increased by-product formation (for example, acetate or ethanol), corroborating the yield drop at low DO.

Why Other Options Are Wrong:

• High yields: Opposite of expected under O2 limitation.
• No effect: Ignores fundamental role of oxygen in energy metabolism.
• None of the above: Not applicable because the correct effect is known.

Common Pitfalls:
Confusing growth rate with yield; DO limitation can reduce both, but yield decreases even if some growth persists via overflow metabolism.

Final Answer:
low biomass yields