OCR AAQ Applied Science • F185 • Lesson 2 • Task 1 preparation

Evidence: What Can a Scene Tell Us?

Biological, physical and trace evidence — and why some evidence narrows a group while other evidence may be much more discriminating.

📖 UCF: Biological Evidence📖 NIJ: Solving Crimes with Soil Bacteria
By the end

You should be able to…

  • classify evidence as biological, physical or trace
  • distinguish class (generic) evidence from potentially individualising evidence
  • explain why evidence value depends on quality and context
  • identify what scientific question a piece of evidence could help answer
Is biological evidence always the strongest evidence?
Evidence landscape

Four ideas that organise the evidence

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

🧬Biological evidenceMaterial from living organisms or biological processes.Click for information
👣Physical evidenceMarks, impressions and objects that can be compared.Click for information
🧵Trace evidenceSmall transferred material such as hair, fibres, soil or paint.Click for information
🎯Class vs individualHow strongly can the evidence narrow the possible source?Click for information
Evidence strength is not a fixed league table. Relevance, condition, quality, quantity, comparison material and corroboration all affect how useful a result is.

Probative evidence

Probative evidence helps prove or disprove something relevant to the investigation.

Ask: What question can this evidence help answer?

A blue fibre is found on a broken window. Useful or useless?
Teacher model

From evidence to a scientific question

Practice item: a muddy shoeprint is photographed beside a forced door.

What can it realistically contribute?

What would make a shoeprint comparison stronger?
Guided practice

Evidence type, strength and sensible conclusions

Press start

Work through the cases one at a time.

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

Independent consolidation

The Community Centre Break-In

A community-centre office has been broken into. Investigators recover a partial shoeprint, three red fibres, a strand of hair, a small blood-like stain and soil from the windowsill.

  1. Classify each item.
  2. Choose two and explain whether they are mainly class evidence or potentially more discriminating.
  3. For each, write one statement it could support and one thing it could not prove alone.

Review notes

  • Biological evidence comes from organisms or biological processes.
  • Physical and trace categories can overlap in real investigations.
  • Trace evidence is often small material transferred during contact.
  • Class evidence associates a sample with a group/category rather than one unique source.
  • Evidence value depends on relevance, quality, quantity, context, method and corroboration.
  • Forensic conclusions should state what evidence supports rather than decide guilt.

Glossary

Why this matters for Task 1

P1 requires students to recognise likely evidence and connect it to relevant forensic-biology disciplines. This lesson gives them the evidence map they need before choosing specialists.

Final checkpoint

Lesson 2 quiz