73. A bacterial culture is grown using 2.0mg/ml fructose as the sole source of carbon and energy.
The bacterial biomass concentrations immediately after inoculation and at the end of the growth
phase are 0.1mg/ml and 0.9mg/ml, respectively. Assuming complete utilization of the substrate,
the bacterial growth yield (𝑌) on fructose is ____

Bacterial Growth Yield on Fructose

Bacterial growth yield on fructose is calculated as the ratio of biomass
produced to substrate consumed. In this case, biomass increased from
0.1 mg/ml to 0.9 mg/ml, while
2.0 mg/ml fructose was completely utilized, giving a yield
value of 0.4. This calculation follows standard microbial
kinetics definitions.

Correct Answer

Step-by-Step Explanation

Bacterial growth yield (Y) measures the efficiency with
which a microorganism converts substrate into biomass. It is defined as:

Given data:

• Initial biomass (X₀) = 0.1 mg/ml
• Final biomass (X) = 0.9 mg/ml
• Initial fructose = 2.0 mg/ml (sole carbon source, fully utilized)

Biomass produced (ΔX):

Substrate consumed (ΔS):

Growth yield:

This means that 40% of the fructose mass is converted into
bacterial dry biomass, a typical value for aerobic heterotrophic growth on
sugars.

Common Options Analysis

In multiple-choice questions, incorrect options often arise from ignoring
initial biomass or misusing the formula.

• 0.4 (Correct): Proper use of ΔX/ΔS.
• 0.05: Uses an incorrect ratio and ignores biomass increase.
• 0.8: Considers only biomass gain, forgets to divide by
  substrate consumed.
• 0.45: Uses final biomass / initial substrate, omitting Δ.
• 2.0: Inverted ratio, implying impossible >100% efficiency.

Exam Relevance

This problem tests understanding of yield coefficients in microbial
kinetics, a core concept in bioprocess engineering and
GATE Biotechnology preparation. Yield values depend on
substrate type and organism but remain constant under defined growth
conditions. Practicing yield calculations alongside Monod growth models
strengthens exam performance.