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Pearson Edexcel IAL Biology 6.2 Measuring microorganism growth

Practise measuring microorganism growth using colony counts, dilution plating, haemocytometers, mass and optical turbidity data.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
A2

Exam points

  • justify serial dilution and plating steps to obtain countable living bacterial colonies
  • calculate cell concentration or ratios from haemocytometer diagrams and culture data
  • distinguish turbidity or optical density from colony counts as total cells versus living cells

6.2—Measuring microorganism growth 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 6.2—Measuring microorganism growth question 1 — Edexcel A-Level Biology A2

The number of bacteria in the samples taken after 10 hours were: 398107171 in the culture of student P 6309573 in the culture of student Q.

Student P and student Q used different methods for determining the number of bacteria. State which method each student used. Give a reason for your answer. (2) Student P Student Q

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