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Edexcel A-Level Biology A2 6.3 Bacterial Growth Curves and Growth Rate Constants Questions

Interpret lag, exponential, stationary and death phases, compare microbial growth rates and calculate the growth-rate constant from log cell data.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
A2

Exam points

  • identify and interpret lag, exponential, stationary and death phases on a bacterial growth curve
  • calculate growth-rate constants or incubation time from log cell numbers and the growth equation
  • compare growth rates using curve gradients, turbidity and changes in living-cell numbers

Edexcel A-Level Biology A2 6.3 Bacterial Growth Curves and Growth Rate Constants Questions question 1

[Maximum number: 2]

Two students, student P and student Q, each cultured bacteria in a liquid medium for 20 hours. The culture conditions used by both students were identical. Every two hours, each student removed a sample of the culture to count the number of bacteria. Each student used a different method to count the number of bacteria in the samples. The graph shows the bacterial growth curve that each student drew using their results. log⁡10\log _{10} number of bacteria per cm3\mathrm{cm}^{3}

Figure for Question Edexcel A-Level Biology A2 6.3 Bacterial Growth Curves and Growth Rate Constants Questions question 1 — Edexcel A-Level Biology A2

Calculate the growth rate constant ( k ) of these bacteria between 2 hours and 6 hours of culture. Use the equation: k=log⁡10Nt−log⁡10N00.301×t\quad k=\frac{\log _{10} N_{t}-\log _{10} N_{0}}{0.301 \times t} where: log⁡10Nt=log⁡10\log _{10} N_{t}=\log _{10} number of cells at 6 hours log⁡10N0=log⁡10\log _{10} N_{0}=\log _{10} number of cells at 2 hours.

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