95. For a chemostat culture operating under steady state, which of the following statements is NOT
true?
1. At a dilution rate equal to maximum specific growth rate, the culture wash out takes place.
2. The dilution rate equals specific growth rate
3. The culture experiences balanced growth
4. The observed growth yield is same as the theoretical growth yield

 

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Question:

For a chemostat culture operating under steady state, which of the following statements is NOT true?

1. At a dilution rate equal to maximum specific growth rate, the culture wash out takes place.

2. The dilution rate equals specific growth rate

3. The culture experiences balanced growth

4. The observed growth yield is same as the theoretical growth yield

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Correct Answer:

4. The observed growth yield is same as the theoretical growth yield

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Explanation:

A chemostat is a continuous culture system where fresh medium is added and culture liquid is removed at the same rate to maintain a constant culture volume and growth environment.

Let’s evaluate each statement:

✅ 1. At a dilution rate equal to maximum specific growth rate, the culture wash out takes place.

• True. When the dilution rate $D$ equals or exceeds the maximum specific growth rate μmax\mu_{\text{max}}μmax, the cells can’t grow fast enough to replenish themselves, resulting in washout.

✅ 2. The dilution rate equals specific growth rate

• True. At steady state, the specific growth rate of the organism is equal to the dilution rate $D$, i.e., $\mu =D$.

✅ 3. The culture experiences balanced growth

• True. Under steady-state conditions, cells grow at a constant rate, and all cellular components increase proportionally, which defines balanced growth.

❌ 4. The observed growth yield is same as the theoretical growth yield

• Not necessarily true. The observed growth yield can differ from the theoretical yield due to:

  • Maintenance energy requirements

  • Substrate inhibition

  • Environmental stresses

  • Limiting nutrient conditions

Thus, Statement 4 is NOT true.

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Conclusion:

In a chemostat under steady state, while growth rate equals dilution rate and cells experience balanced growth, observed growth yield may differ from theoretical yield, making Option 4 the correct answer to the question.