In a nutrient broth at 37 °C, a strain of *E. coli* without a plasmid grows from $2\times10^{6}$ cells ml⁻¹ to $1.6\times10^{9}$ cells ml⁻¹ in 8 h. The same strain carrying a plasmid that confers resistance to a sub‑lethal concentration of an antibiotic grows from $2\times10^{6}$ cells ml⁻¹ to $5.0\times10^{8}$ cells ml⁻¹ in the same 8 h period. Assuming exponential growth, calculate the generation time for each strain. Then, if both cultures are allowed to grow for a total of 24 h under the same conditions, which strain will have the greater final cell density and by what approximate factor?

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Generation times: ≈0.83 h for the plasmid‑free strain and ≈1.00 h for the plasmid‑bearing strain. After 24 h the plasmid‑free culture will have roughly 32 times the cell density of the plasmid‑bearing culture.

Neco Model Questions Vol1 2019 Biology Question 32

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