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Edexcel IAL Biology 6.3 Growth curves and rate constants

Label both axes and four phases, select values from the exponential section and substitute logarithmic cell counts and elapsed time into the stated equation.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
A2

Exam points

  • Sketch a growth curve with labelled axes and lag, exponential, stationary and death phases.
  • Calculate a growth rate constant from log cell counts and elapsed culture time.
  • Compare exponential growth using graph gradients, turbidity or concentration trends.

6.3—Bacterial growth curves and growth rate constants 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 6.3—Bacterial growth curves and growth rate constants 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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