OCR AAQ Applied Science • F185 Forensic Biology • Lesson 1

The Forensic Toolkit

What is forensic biology, what can it really tell us, and why does every investigation need the right specialist for the evidence?

▶ An Intro to Forensics: The Science of Crime (9 min)
OCR SOW suggested opening video — useful either as a hook or after the starter.
Today

By the end you should be able to…

  • define forensic science and forensic biology;
  • explain the difference between criminal and civil law;
  • explain Locard’s exchange principle;
  • name the major branches of forensic biology and describe what each broadly investigates;
  • select a sensible forensic specialist for a piece of evidence.
What do forensic scientists actually do?

Write one sentence. Avoid TV-show language.

The big picture

Forensic science is bigger than “solving crimes”

Forensic science

The application of science to questions in criminal and civil law.

It can include biology, chemistry, physics, digital evidence, toxicology, document analysis and many other specialist areas.

⊃

Forensic biology

A part of forensic science concerned with biological material and biological processes that may provide evidence.

Examples include blood, saliva, hair, microorganisms, plant material, bones, teeth and insects.

Important: not all forensic evidence is biological, and not every investigation needs every branch of forensic biology.
📖 Types of Forensic Science (OCR SOW: ~5 min read) 🔬 Forensic Biology – CFSRE 🧑‍🔬 Forensic scientist career profile

Criminal law

Concerns alleged offences against the law. Forensic evidence may help establish what happened, connect people or objects, exclude possibilities, or test an account.

Examples: theft, assault, criminal damage.

Civil law

Concerns disputes between people or organisations. Scientific evidence can still be important even where no criminal offence is being prosecuted.

Examples: negligence, product disputes, some workplace or medical claims.
Criminal or civil?

A company claims a laboratory supplier sold contaminated material that caused financial loss.

▶ Civil and criminal law explained (under 2 min) 📖 Criminal vs civil law (OCR SOW: ~10 min read)
A major misconception

What forensic scientists do not decide

They can…

observe, measure, compare, test and interpret scientific evidence.

They can…

explain the strength, limitations and uncertainty of their findings.

They cannot…

decide guilt.

That is a legal judgement, not a scientific test result.

▶ Forensic Science – Last Week Tonight (caution does have swearing...) (18 min) 📖 6 forensic science myths 📖 The CSI effect in forensic science
Teacher option: the Last Week Tonight clip is suggested by OCR as a longer discussion starter about how forensic science is portrayed in the media. Preview it first and use selected sections if that suits your group.
Locard's exchange principle

“Every contact leaves a trace”

When two people, objects or environments come into contact, material may be transferred between them.

This principle helps explain why trace evidence may exist.

But: transfer does not guarantee useful evidence will still be present later. Material can be lost, cleaned away, degraded or contaminated.
Person A Person B shared surface Contact can transfer material in both directions
▶ Locard’s Exchange Principle (OCR SOW: ~2 min) 📖 How Locard’s Exchange Principle works (OCR SOW: ~3 min read) 📖 Principles of Trace Evidence (OCR SOW: ~3 min read)

Locard ≠ trace evidence

Locard's principle is the broader idea that contact can cause transfer.

Trace evidence is material that may be transferred and recovered, such as hairs, fibres, soil, paint or small particles.

MWB: Give one example of transfer in each direction.

A person climbs through a broken garden window.

▶ Locard’s Exchange Principle – deeper explanation (teacher/stretch) 🧪 A practical way to teach Locard
Forensic biology is a huge field

Eight branches you should know exist

Click a panel. Information appears immediately — no extra reveal.

🩸SerologyBlood and other bodily fluidsWe will revisit this
🫀PathologyDisease, injury and cause of deathWider field
🦴AnthropologySkeletal evidenceWider field
🦷OdontologyTeeth and dental evidenceWe will revisit this
🌿BotanyPlant materialWider field
🦠MicrobiologyMicroorganisms and microbial evidenceWe will revisit this
🪶OrnithologyBirds and feathersWider field
🪰EntomologyInsects and their life cyclesWider field
📖 Explore more forensic disciplines 🔬 Explore forensic biology
Evidence is not all equally powerful

Class evidence and individual evidence

Class / generic evidence

Places an item or sample into a group or category, but normally cannot by itself identify one unique source.

Examples: a common fibre type, blood group, a common shoe-tread design.

Potentially individualising evidence

May contain enough distinctive information to associate evidence much more strongly with one source, if quality and comparison conditions are good.

Examples: a high-quality fingerprint with sufficient ridge detail; a suitable DNA profile.

This distinction is deliberately simplified today. Evidence strength depends on quality, quantity, context, method and uncertainty. We will return to this later.
Guided practice

Which forensic specialist?

Practice case

Press start.

These are separate practice cases, not the assessed scenario.

🗂 Mesa Police mock crime-scene resource
Worked example

How experts think

Practice evidence: insect larvae are recovered from human remains outdoors.

Evidence→ Relevant branch→ What it may tell us→ Limitation
Why is “call every forensic specialist” a poor investigation plan?
Independent consolidation

A different case: The Laboratory Break-In

A teaching laboratory is broken into overnight. A small blood-like stain is found on broken glass. A muddy shoeprint is photographed beside the window. A strand of hair and several blue fibres are recovered from a torn curtain. A potted plant has been knocked over and soil is spread across the floor.

Your task

  1. Identify three types of evidence that may be useful.
  2. For each, suggest a suitable forensic branch or analysis approach.
  3. State one thing the evidence could tell investigators.
  4. State one limitation or reason to be cautious.
Student review notes

Everything you need from Lesson 1

Core ideas

  • Forensic science = applying science to questions in criminal and civil law.
  • Forensic biology = the biological part of forensic science.
  • Locard: contact can transfer material between people, objects and environments.
  • Transferred material may later be lost, degraded, cleaned or contaminated.
  • Forensic scientists interpret evidence; they do not decide guilt.

The eight branches

Serology • Pathology • Anthropology • Odontology • Botany • Microbiology • Ornithology • Entomology

Different investigations need different specialists. Evidence should drive the choice.

Why this matters later

One of the skills assessed in F185 is recognising potential evidence, identifying the forensic biology disciplines required for an investigation, and explaining how those disciplines could help. Today builds the map; later lessons build the detail.

🕵️ University of Portsmouth CSI online activity 🧑‍🔬 Explore a forensic scientist career

Glossary

Click for an instant definition.

Exit MWB: explain Locard in 15 words or fewer.
Final checkpoint

Lesson 1 quiz

10 questions. Options are shuffled each time you restart.