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Edexcel IAL Biology Topic 6 Microbiology and immunity

Choose the correct culture or measurement method, interpret microbial and immune data and connect pathogen structures or transmission routes to host defence outcomes.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
A2

Exam points

  • Justify aseptic culture, dilution plating and microbial measurement methods.
  • Interpret growth curves, colony counts or turbidity and calculate growth constants.
  • Link pathogen structure and transmission evidence to barriers and immune responses.

Covered syllabus points

6.1—Culturing microorganisms and aseptic technique6.2—Measuring microorganism growth6.3—Bacterial growth curves and growth rate constants6.4—Core Practical 13 - microorganism growth rate6.5—Bacteria, viruses, lytic cycle and latency6.6—Mycobacterium tuberculosis and HIV infection6.7—Pathogen entry routes and barriers6.8—Non-specific responses to infection6.9—Antigens, antibodies and immune response6.10—B cells and T cells6.11—Natural, artificial, active and passive immunity6.12—Evolutionary race between pathogens and hosts6.13—Bacteriostatic and bactericidal antibiotics6.14—Core Practical 14 - antibiotics and bacteria6.15—Hospital-acquired infections and practice codes6.16—Microorganisms in decomposition and carbon recycling6.17—PCR amplification of DNA6.18—Gel electrophoresis of DNA fragments6.19—DNA profiling6.20—Determining time of death

Topic 6 - Microbiology, Immunity and Forensics question 1

[Maximum number: 8]

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 Topic 6 - Microbiology, Immunity and Forensics question 1 — Edexcel A-Level Biology A2

Question (a)

(a)

Both students used aseptic techniques to culture the bacteria.

[ 4 ]

Question (i)

(i)

Explain the importance of using aseptic techniques to culture bacteria.

[ 2 ]

Question (ii)

(ii)

Explain one aseptic technique that should be used when culturing bacteria.

[ 2 ]

Question (b)

(b)

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.

[ 2 ]

Question (c)

(c)

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.

[ 2 ]

Question (i)

(i)

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

[ 2 ]
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