In microbial physiology and bioprocess engineering, “balanced growth” is best defined as a growth state in which a population increases while maintaining a constant overall chemical composition and a constant specific growth rate. Which statement matches this definition most accurately?

Difficulty: Easy

Correct Answer: cultures undergoing balanced growth while maintaining a constant chemical composition

Explanation:


Introduction / Context:
Balanced growth is a foundational concept in microbiology and bioprocess engineering. It refers to a physiological state where every measurable component of the cell population (RNA, DNA, proteins, lipids, metabolites) increases in fixed proportion, so the overall composition remains constant while cell numbers and biomass rise exponentially. Understanding this state is critical for designing reproducible experiments and scalable fermentation processes.


Given Data / Assumptions:

  • A well-mixed, nutrient-replete environment (for example, early exponential phase or steady-state chemostat) is considered.
  • No limiting toxic byproducts accumulate during the observation window.
  • Specific growth rate (mu) is constant.
  • Macromolecular composition per cell remains constant over time.


Concept / Approach:
In balanced growth, cellular synthesis is coordinated. Ratios such as RNA/protein or protein/DNA do not drift, and the cell size distribution is stable. This contrasts with “unbalanced growth,” where a shift in nutrients, temperature, or pH causes compositional changes. Experimentalists often enforce balanced growth via continuous culture (chemostat) at fixed dilution rate and feed composition, producing steady-state conditions.


Step-by-Step Solution:
Identify the key hallmark: constant chemical composition while biomass increases. Link it to constant specific growth rate under steady conditions. Evaluate options: only one statement captures both growth and compositional constancy. Select the definition that directly states “cultures undergoing balanced growth while maintaining a constant chemical composition.”


Verification / Alternative check:
In a chemostat at steady state, cell composition, substrate concentration, and growth rate remain constant over many residence times—an empirical confirmation of balanced growth.


Why Other Options Are Wrong:

  • Controlling pH or temperature: Important operational controls, but they do not define balanced growth by themselves.
  • Changing nutrient composition: Typically induces unbalanced growth due to physiological shifts.


Common Pitfalls:
Confusing stable culture conditions (for example, constant pH) with true balanced growth. The essence is proportional synthesis and constant composition, not merely environmental control.


Final Answer:
cultures undergoing balanced growth while maintaining a constant chemical composition.

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