In microbial growth kinetics, the specific growth rate μ is influenced by multiple environmental and process factors. Which set best captures its main dependencies?

Introduction / Context:
The specific growth rate μ (per hour) describes how rapidly biomass increases per unit biomass. It is central to Monod-type models and bioreactor design. This question checks your understanding that μ depends on more than just the carbon source, especially in real reactors where inhibition and oxygen transfer constraints appear.

Given Data / Assumptions:

• Organism may be aerobic (thus oxygen transfer can limit μ).
• Substrate can be limiting (Monod behavior).
• Products (e.g., organic acids, ethanol) may inhibit at high concentrations.

Concept / Approach:
In a simplified Monod model, μ = μ_max * S / (K_s + S). Practical kinetics extend this to include inhibition terms (product inhibition, substrate inhibition) and oxygen limitation (e.g., dependence on dissolved oxygen C_O2 via a saturation function). Hence, μ responds to substrate availability, product buildup, and oxygen transfer/solubility constraints.

Step-by-Step Solution:

Verification / Alternative check:
Chemostat experiments commonly report μ varying with inlet S, aeration/kLa, and product concentration; engineering models incorporate all three.

Why Other Options Are Wrong:

• Single-factor views (S only, P only, O2 only) ignore well-known multi-factor control.
• Agitation alone matters only through its effects on transfer; chemistry still rules.

Common Pitfalls:
Overfitting a Monod curve without checking inhibition or oxygen limitation.

Final Answer:
All of these: substrate, inhibitory products, and oxygen supply.