OCR AAQ Applied Science • F185 • Lesson 3 • Task 1 preparation

Serology: Blood and Bodily-Fluid Evidence

What serology contributes to an investigation — and how to avoid turning a test result into a claim it cannot support.

📖 OCR SOW: What is Serology?▶ Serology Blood Test / Serologic Tests (3 min)▶ What is a pathologist? (1 min, wider field)
By the end

You should be able to…

  • explain what forensic serology studies
  • identify blood, saliva and urine as bodily fluids relevant to forensic biology
  • explain the purpose of presumptive testing at an introductory level
  • write a cautious interpretation of a positive screening result
A stain gives a positive presumptive test for blood. What can you say?
Relevant branch

Serology: what does it investigate?

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

🩸SerologyBodily-fluid evidence and serological testing.Click for information
🔴Blood evidenceA biological fluid containing cells and other components.Click for information
💧Saliva / other fluidsBiological material can include cells and detectable components.Click for information
🧪Presumptive testingScreening suggests possible presence; it is not final proof.Click for information
Wider field: pathology is another forensic-biology branch, but it examines disease, injury and tissue changes. We acknowledge it without turning it into a full unit here.

Antigens and antibodies — enough for today

Antigens can be recognised by specific antibodies. Serological tests can use that specificity.

Focus on the idea of specific detection, not an immunology degree.

Why use a screening test before a more specific test?
Teacher model

Interpreting a stain result

A reddish-brown stain from a fictional office break-in gives a positive presumptive blood result.

How should it be reported?

Why is “this is the suspect’s blood” too strong?
Guided practice

What does the result actually support?

Press start

Work through the cases one at a time.

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

Independent consolidation

The Changing-Room Incident

Three stains are recovered: A is reddish-brown, B is colourless on a drinks bottle and C is yellowish on a floor tile.

  1. Suggest a possible bodily fluid for each.
  2. Explain why appearance alone is insufficient.
  3. Write a cautious sentence after a positive presumptive blood result for A.
  4. State why follow-up testing could be useful.

Review notes

  • Forensic serology concerns blood and other bodily fluids.
  • Blood, saliva and urine are bodily fluids students should recognise in F185.
  • Presumptive tests are screening tests and may require confirmation/further analysis.
  • Antigen–antibody interactions can provide specific detection.
  • A forensic result should say what is supported and what remains uncertain.
  • Pathology is related but different: disease, injury and tissue changes.

Glossary

Why this matters for Task 1

P1 may require students to identify serology where bodily-fluid evidence is likely. P3/M2 later require an analysis plan and a reason why the chosen method is appropriate.

Final checkpoint

Lesson 3 quiz