Q.75
Chemostat is a continuous culture system in which sterile medium is fed into the culture vessel at the same rate as the spent medium is removed.
If in a chemostat culture, the flow rate is 30 ml h−1 and volume of the medium inside the vessel is 100 ml,
the dilution rate in h−1 is
Introduction
A chemostat is a continuous culture system where fresh sterile medium
enters the vessel and spent medium leaves at the same rate. The culture volume remains constant.
The most important parameter controlling microbial growth is the
dilution rate (D).
Let us calculate the dilution rate step-by-step.
Given
Flow rate (F) = 30 ml h-1
Culture volume (V) = 100 ml
Find: Dilution rate (D)
Formula
Dilution rate:
D = F / V
where,
- D = dilution rate (h-1)
- F = flow rate (ml h-1)
- V = culture volume (ml)
Step-by-Step Calculation
Step 1: Substitute values
D = 30 / 100
Step 2: Solve
D = 0.30 h-1
Final Answer
0.30 h-1
Correct Option: (D)
Explanation of All Options
- (A) 3.33 – Calculated V/F instead of F/V (incorrect)
- (B) 1.50 – Wrong substitution or arithmetic mistake
- (C) 0.75 – Incorrect division
- (D) 0.30 – Correct using D = F/V
Conceptual Understanding
In a chemostat at steady state:
μ = D
where μ is the specific growth rate.
Higher dilution rate may cause washout of cells,
while lower dilution rate supports steady growth.
Exam Trick
Always remember:
D = F / V
Direct substitution saves time in competitive exams.
