OCR AAQ Applied Science • F185 • Lesson 5 • Task 1 preparation

Forensic Microbiology: Soil and Microbial Evidence

Using microorganisms as comparative forensic evidence without pretending a school agar plate uniquely identifies a place or species.

📖 NIJ: Solving Crimes with Soil Bacteria📖 Microbial Succession as a Forensic Tool📖 NIJ: The Forensic Microbiome
By the end

You should be able to…

  • explain what forensic microbiology investigates
  • describe how soil microorganisms can support sample/location comparisons
  • describe colony morphology using size, shape, colour and surface appearance
  • state limitations of school-level microbial comparison
Can two soil samples look similar but contain different microbial communities?
Relevant branch

Microbiology in the forensic toolkit

Click each information panel. It opens straight to the information — no extra reveal.

🦠Forensic microbiologyMicroorganisms and microbial communities as evidence.Click for information
🌍Soil microbiologySoil carries communities that can vary between locations.Click for information
🧫Colony morphologySize, shape, colour and surface appearance.Click for information
⚠️Limits of school methodsMorphology is comparative evidence, not species proof.Click for information
Wider field: forensic microbiology also includes decomposition research, microbiomes and biosecurity. Our working focus is the comparison of cultured soil/microbial evidence.
Visual model

What does colony morphology mean?

Plate A

Plate B

What four colony features would you record?
Teacher model

Questioned soil culture vs references

A questioned culture contains three dominant colony appearances. Reference A shows the same three broad morphologies; B and C differ substantially.

Can we say the questioned soil definitely came from Reference A's location?
Guided practice

Compare microbial evidence cautiously

Press start

Work through the cases one at a time.

These are parallel practice examples, not the live set assignment.

Independent consolidation

The Muddy Boot Comparison

FeatureQuestionedRef ARef BRef C
Large orange circular colonyPresentPresentAbsentPresent
Small cream smooth colonyPresentPresentPresentAbsent
Green irregular colonyPresentPresentAbsentAbsent
  1. Which reference is most consistent?
  2. Use the table to justify.
  3. Explain why morphology alone does not prove a unique source.

Review notes

  • Forensic microbiology uses microorganisms and microbial communities as evidence.
  • Soil contains microorganisms and can be compared between questioned and reference samples.
  • Colony morphology is described using size, shape, colour and surface appearance.
  • Similar morphology can support an association but does not identify species or a unique location.
  • Sampling, culture medium and incubation conditions affect what grows.
  • Aseptic technique and practical culture safety will be revisited before Task 3.

Glossary

Why this matters for Task 1

Microbiology is especially relevant because Task 3 requires microbiological analysis. For Task 1, students need enough knowledge to choose and justify a workable cultured-soil comparison.

Final checkpoint

Lesson 5 quiz