Section 4: Bioprocess Engineering and Process Biotechnology
Bioreactor types, scale-up
Subtopic: Fundamentals of Bioreactor types, scale-up
Question Statement:
Which of the following factors can affect the growth of a microbial culture in a
batch cultivation process?
Options:
(A) pH of the medium
(B) Osmolarity of the medium
(C) Substrate concentration in the medium
(D) Substrate feed rate
Official Answer Key:
A;B;C
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.52)**
**1. Governing Concept**:
- **Topic**: Microbial Kinetics & Environmental Factors in Batch Fermentation
- Microbial specific growth rate ($\mu$) and biomass yield in a batch bioreactor depend on physicochemical and nutritional parameters:
1. **Temperature**: Influences enzyme kinetics (Arrhenius behavior) and membrane fluidity.
2. **pH**: Dictates transmembrane proton motive force, protein ionization state, and enzyme activity.
3. **Dissolved Oxygen (DO)**: Crucial terminal electron acceptor in aerobic respiration; low DO triggers oxygen limitation or metabolic shifts.
4. **Initial Inoculum Size**: Determines the duration of the lag phase and rate of substrate consumption.
**2. Option Analysis**:
- **Option (A) [Temperature of the culture medium] is CORRECT**: Growth follows cardinal temperatures ($T_{\min}, T_{\text{opt}}, T_{\max}$).
- **Option (B) [pH of the culture medium] is CORRECT**: Deviations from optimal pH severely curtail specific growth rate.
- **Option (C) [Dissolved oxygen concentration in aerobic culture] is CORRECT**: Sub-critical dissolved oxygen limits respiratory ATP synthesis and biomass production.
- **Option (D) is INCORRECT**: Invariant geometric constants do not govern cellular biological growth rate directly if mixing and mass transfer remain unconstrained.
**3. Final Answer**:
- **Correct Options**: **A, B, C**
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