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Edexcel A-Level Biology A2 6.2 Measuring Microorganism Growth Questions

Measure microbial growth with serial dilution and colony counts, optical density or haemocytometer methods, then compare accuracy and limitations.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
A2

Exam points

  • use serial dilution, dilution plating and colony counts to measure viable microbial numbers
  • use optical density, calibration curves and haemocytometer counts to estimate microbial concentration and growth
  • compare microbial measurement methods, including living versus total cells and concentration-dependent accuracy

Edexcel A-Level Biology A2 6.2 Measuring Microorganism Growth 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 6.2 Measuring Microorganism Growth Questions 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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