Question

Bacillus cereus divides every 30 minutes. You inoculate a culture with exactly 100 bacterial cells. After 3 hours, how many bacteria are present and what is the generation number and time?

(a) (24,000), (3 generations), (30 minutes per generation)

(b) (64,000), (6 generations), (30 minutes per generation)

(c) (24,000), (6 generations), (60 minutes per generation)

(d) (64,000), (3 generations), (60 minutes per generation)

I had been asked this question in a national level competition.

I want to ask this question from Graph Paper with Logarithmic Coordinates in section Presentation and Analysis of Data of Bioprocess Engineering

Answer 1

Correct choice is (b) (64,000), (6 generations), (30 minutes per generation)

The best I can explain: Number of cells:

In 3 hours, B.cereus will divide 6 times. Therefore, n=6.

2^6 = 64 or 2 × 2 × 2 × 2 × 2 × 2.

100×64=64,000cells.

Number of generations:

Number of generations = [log (cells at the end of incubation)]-[log (cells at the beginning of incubation)]/0.301.

Therefore, [(log 6400) – (log 100)]/0.301 = (3.81-2)/0.301 = 6 generations.

Generation time:

60 min×3 hours / 6 generations = 30 minutes per generation.