Analyze trace evidence
Do now
Analyze your trace-evidence observations with a CER and evaluate documentation limitations.
- Hand in
- CER arguing what the trace evidence suggests about the scene, using Wednesday's microscopy observations as evidence and acknowledging at least one limitation.
- Where
- Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
You get two school days for every day you were absent, so this deadline moves with you.
Your fiber matches the description of the suspect's jacket. Does that prove the suspect was at the scene, and what would you need before you could even say that?
Analyze your trace-evidence observations with a CER and evaluate documentation limitations.
- • I can write a CER from trace-evidence observations.
- • I can identify limitations in evidence interpretation.
- Why is an observation of a fiber not the same as identifying it?
- Name one thing your still cannot prove even if it matches a suspect's clothing.
- 1Compare your trace-evidence descriptions to reference characteristics.
- 2Write a CER: what does this suggest about the scene?
- 3Evaluate whether your chain-of-custody log would hold up to scrutiny.
- 4List two variables that could change trace-evidence interpretation.
- 5State one limitation of as a sole source of proof.
What did this day actually feel like?
Analyze trace evidence
We took our observations under magnification and compared them to reference characteristics, then wrote a CER about what the trace evidence suggests about the scene.
The hard part was the last step, which was auditing our own chain of custody and asking whether it would survive someone attacking it. Ours would not, because of the photo problem on Wednesday. Writing down honestly that our own evidence had a weakness felt bad, and he said that is exactly what a real analyst has to do, because the alternative is being surprised by it in court.
My CER is getting better. The reasoning sentence now explains why the evidence supports the claim instead of just restating it. That took three weeks.
Turned in: CER → Claim Evidence Reasoning folder
Fiction. There is no such student. The lessons, labs and dates are the real planned course; the student, the classmates and the conversations are invented.
The same day, drawn.
We reshot and logged both versions. It cost us the period.
MR. MENDOZA
The fix was not better photography. Three of you worked in parallel and nobody sequenced it.
Fiction. There is no such student. The lessons, labs and dates are the real planned course; the student, the classmates and the conversations are invented.
🛠 Get unstuck · pick your level
🔑 Today's words · 5
Tap a word in the lesson for a plain meaning and one example. Recycled into next week's Do-Now.
Reasoning: connecting evidence to the claim
What separates sound reasoning from bad reasoning, and how do you check your own?
Reasoning is the part where you explain why your evidence supports your claim. It is the bridge. Without it, a claim and some data are just sitting next to each other; reasoning shows how the data leads to the conclusion, often using a scientific principle.
Good reasoning is logical (each step follows from the last), it actually uses your evidence (not just restates the claim), and it considers alternatives (could the data mean something else?). Bad reasoning leans on logical fallacies: jumping to conclusions, confusing correlation with causation, or attacking the person instead of the idea.
Check your own reasoning by trying to break it: state the opposite and see if your evidence rules it out. Ask “what would have to be true for me to be wrong?” If you cannot answer, your reasoning is not finished yet.
- • Logical: each step follows from the one before it.
- • Grounded: it uses your evidence, and names the principle that links it to the claim.
- • Fair: it considers other explanations and says why yours is better.
- • Self-checked: you tried to prove yourself wrong and could not.
- • Correlation is not causation: two things moving together does not mean one caused the other.
- • Hasty generalization: one case does not prove a rule.
- • Ad hominem: attacking the person, not their evidence.
Write the reasoning that links your evidence to your claim from earlier this week. Then write the strongest objection to it, and answer that objection.
Do the work · 80-minute blockfirst 5 min = hook▸
💡 Big idea: Observations become evidence only when compared to a reference and bounded by their limits, because corroborates a convergent chain rather than proving guilt alone.
- 0:00Return Wednesday scene packets; review the chain-of-custody log together
- 0:10Reference comparison: project reference fiber and hair characteristics; students compare their sketches
- 0:28CER writing: claim about what the suggests, evidence from observations, reasoning from comparison
- 0:50Chain-of-custody audit: students check their own log for missing fields; flag gaps
- 1:02List two variables that could change interpretation; state one limitation of alone
- 1:10Pair-share CERs; preview Friday submission
- • You collected yesterday. Now comes the harder question: what does it actually mean? A fiber is not evidence of anything by itself until you compare it to something else.
- • Today you will use reference images to compare your trace observations. If your fiber matches the reference for a known sample, that is meaningful. If it does not, that is also meaningful.
- • Then you will audit your own chain-of-custody log. Could a defense attorney find a gap? An unsigned field? A time that is out of sequence? If yes, the evidence might not make it to court.
- • Finally, you will write a CER. This is your scientific argument: here is what I observed, here is why it matters, and here is what it cannot prove.
- • must be compared to reference standards (known samples) to have meaning; an observation alone is not identification.
- • Two key variables that affect trace-evidence interpretation are the condition of the sample (degraded vs. intact) and the analyst's reference library.
- • rarely proves guilt alone; it corroborates other evidence in a convergent chain.
Unit 1.1 Investigating the Scene: Forensic scene documentation, evidence log, crime-scene sketch, trace evidence, biometric data. · Analyze
Day 4 of this lesson. Open this exact section in myPLTW (find it in Clever, Microsoft sign-in), then do the work below.
Do this: In myPLTW, complete the Lesson 1.1 Investigating the Scene analysis reflection section.
Mark the Lesson 1.1 scene-analysis reflection complete in myPLTW.
You built the scene packet Wednesday. By the end of today your CER and chain-of-custody audit should both be finished.
Completed CER (written or typed) and annotated chain-of-custody log with any gaps flagged.
The official PLTW activity stays inside myPLTW. If myPLTW will not open, use F1 and E1-E3 on this page to complete today's local evidence decision, then make up the official activity when access returns. Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
Check things off as you work, then submit. This tells Mr. Mendoza how you're doing so he can help the class. It does not replace turning in your producible through the submission route shown below.
Use the code Mr. Mendoza gave you, not your name. Saved on this device.
Unit 1.1 Investigating the Scene: Forensic scene documentation, evidence log, crime-scene sketch, trace evidence, biometric data. · Analyze trace evidence
In myPLTW, complete the Lesson 1.1 Investigating the Scene analysis reflection section.
You built the scene packet Wednesday. By the end of today your CER and chain-of-custody audit should both be finished.
This is how Mr. Mendoza sees the class keeping pace with PLTW. Be honest, it only helps if it is accurate.
🎯 Analyze your trace-evidence observations with a CER and evaluate documentation limitations.
- Compare your trace-evidence descriptions to reference characteristics.
- Write a CER: what does this suggest about the scene?
- Evaluate whether your chain-of-custody log would hold up to scrutiny.
- List two variables that could change trace-evidence interpretation.
- State one limitation of as a sole source of proof.
CER: CER arguing what the suggests about the scene, using Wednesday's microscopy observations as evidence and acknowledging at least one limitation.
Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not. Use the checklist just below and upload by 11:29 PM for full credit. Absent with an excused absence? You get two school days for every day you were absent, so this deadline moves with you.
| Task | Who |
|---|---|
| Compare your trace-evidence descriptions to reference characteristics. | _______ |
| Write a CER: what does this suggest about the scene? | _______ |
| Evaluate whether your chain-of-custody log would hold up to scrutiny. | _______ |
| List two variables that could change trace-evidence interpretation. | _______ |
| State one limitation of as a sole source of proof. | _______ |
Working solo? Put your own name in "Who" for every row.
- I can write a CER from trace-evidence observations.
- I can identify limitations in evidence interpretation.
- 1Do thisAnalyze your trace-evidence observations with a CER and evaluate documentation limitations.
- 2Use this resource
- 3Submit thisCER: CER arguing what the trace evidence suggests about the scene, using Wednesday's microscopy observations as evidence and acknowledging at least one limitation.
- 4Submit it here
- 1Open the drop folder.
- 2Sign in with your district Microsoft account, not a personal one.
- 3Upload the file, named Lastname_Firstname__Assignment Title.
- 4Your own upload panel says Uploaded with a green check: that is your receipt.
Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not. Principles of Biomedical Technology (Principles of Biomedical Science) › Unit 1.1 Investigating the Scene: Forensic scene documentation, evidence log, crime-scene sketch, trace evidence, biometric data. › CEROpen the drop folder
Learn it · deck, reading, and vocabulary▸
The deck carries the prior idea forward, lets you inspect an analogy, maps the rule to biology, and ends with the same evidence decision and exit ticket used on this page.
Generated from this lesson's canonical data with a red-team citation check.
Scene documentation works only as a team SOP, because a missing scale marker, unlogged item, or unrecorded magnification anywhere breaks the chain and weakens everyone's evidence.
Observations become evidence only when compared to a reference and bounded by their limits, because corroborates a convergent chain rather than proving guilt alone.
A detective board holds observations, possible explanations, and one next question.
- Which notes are direct observations?
- Which notes are explanations?
- What new evidence would separate the explanations?
Keep observations separate from explanations, then collect the evidence that can distinguish the options.
Biomedical investigations use controlled procedures and validated measurements, not intuition alone.
- • Board notes map to E1-E3.
- • Possible explanations map to the decision options.
- • The next question maps to the evidence-based action.
Driving question: Your fiber matches the description of the suspect's jacket. Does that prove the suspect was at the scene, and what would you need before you could even say that?
What you already know: Scene documentation works only as a team SOP, because a missing scale marker, unlogged item, or unrecorded magnification anywhere breaks the chain and weakens everyone's evidence.
New idea: Observations become evidence only when compared to a reference and bounded by their limits, because corroborates a convergent chain rather than proving guilt alone.
Visual or model: F1. F1. A lesson illustration or teaching diagram for Analyze trace evidence. Use it with E1-E3; it is a model or context image, not experimental or patient data. What to notice: Trace the labeled observation or evidence sequence before choosing an explanation.
- Observe or measure the relevant feature in Analyze .
- Organize the observation with a stable evidence ID.
- Apply this rule: Keep observations separate from explanations, then collect the evidence that can distinguish the options.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: Your fiber matches the description of the suspect's jacket. Does that prove the suspect was at the scene, and what would you need before you could even say that?
What the evidence supports: E1-E3 and F1 support the daily take-home when the response meets the stated success criteria.
What it cannot prove: The package does not support claims beyond this lesson's or any real patient diagnosis.
- • : Relating to the use of science to examine evidence and answer questions in legal investigations, such as identifying a person or cause of harm.
- • : Tiny physical materials, such as hair, fibers, or soil, transferred during contact at a scene, used to link people, places, and objects in an investigation.
- • biometric: A measurable physical or behavioral trait, such as a fingerprint, iris pattern, or heart rate, used to identify a person or track health.
- • observation: Information gathered directly through the senses or instruments, recording what actually happens without yet interpreting it.
- • inference: A conclusion drawn by reasoning from evidence and observations rather than from direct, firsthand measurement.
- • : The documented record of who handled a piece of evidence, when, and where, proving it was never lost, swapped, or tampered with.
- • : A reference sample treated like the others but without the variable being tested, giving a baseline to compare experimental results against.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
must be compared to reference standards (known samples) to have meaning; an observation alone is not identification.
Limit: E1 supplies context or an observation; it does not by itself establish the explanation.
Observations become evidence only when compared to a reference and bounded by their limits, because corroborates a convergent chain rather than proving guilt alone.
Limit: E2 is a teaching statement or comparison and must be checked against the task evidence.
I can write a CER from trace-evidence observations.
Limit: E3 supports only the result or product criterion named here; it cannot justify a broader clinical or causal claim.
PLTW-PBT-2026-09-14 · Simulated classroom evidence scenario
Your role: biomedical investigator
Decision: Your team must decide what the evidence from Analyze supports before submitting the claim-evidence-reasoning response named on the lesson page.
- • Choose the strongest supported explanation.
- • Choose the next evidence to collect.
- • Hold the decision because the evidence is insufficient.
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Submit it as the claim-evidence-reasoning response.
Claim ceiling: The supplied lesson evidence can support an observation, pattern, classroom mechanism, or next-step decision about Analyze . It cannot by itself prove causation, establish a real clinical diagnosis, or justify action outside this classroom task.
Reason for review: Your team must decide what the evidence from Analyze supports before submitting the claim-evidence-reasoning response named on the lesson page.
Context: An observation only becomes evidence when it is compared to a known reference and its limits are stated, because corroborates a story but rarely proves guilt by itself.
- • T1: Compare your trace-evidence descriptions to reference characteristics.
- • T2: Write a CER: what does this suggest about the scene?
- • T3: Evaluate whether your chain-of-custody log would hold up to scrutiny.
- • T4: List two variables that could change trace-evidence interpretation.
- • T5: State one limitation of as a sole source of proof.
- • E1: must be compared to reference standards (known samples) to have meaning; an observation alone is not identification.
- • E2: Observations become evidence only when compared to a reference and bounded by their limits, because corroborates a convergent chain rather than proving guilt alone.
- • E3: I can write a CER from trace-evidence observations.
Measurements: Use only the measurements, units, graph, or counts supplied in today's task. No additional patient measurement is implied.
Figure finding: Teaching diagram for Analyze . Trace the labeled observation or evidence sequence before choosing an explanation. This is a teaching model, not patient or experimental data.
Uncertainty: This is a composite classroom scenario. Missing history, measurements, or confirmation tests remain unknown and limit the conclusion.
Mean = sum of values / number of values. Median = middle ordered value. Range = maximum - minimum.
For 2, 4, 4, and 10: mean = 20 / 4 = 5, median = 4, and range = 10 - 2 = 8.
Mean, median, and range keep the measurement unit. Order the values before finding the median.
Calculate the requested summary for today's supplied values, then write what it reveals and what it hides.
Students often think Students think that if their matches a suspect's clothing or hair, that match proves the suspect was at the scene.. The trap: A match to a common fiber or hair type is corroboration, not proof, because many people own the same materials and trace can transfer indirectly. It strengthens a case only when it converges with other evidence, and it never stands alone as identification.
Claim: The shoe impression lifted from the scene is consistent with a size 10 athletic-tread pattern, but on its own it cannot identify a specific shoe or the person who wore it.\nEvidence: When I measured the cast and compared it to the reference chart, the impression showed a wavy zig-zag tread and an overall length near 30 centimeters, which match the reference characteristics for a size 10 running shoe rather than a flat-soled dress shoe.\nReasoning: Comparing my measurement to a known reference is what turns a mark in the dirt into a usable class characteristic, since an impression by itself is just a shape. The match narrows the possibilities to one common shoe type, but a factory makes thousands of identical soles, so a shared tread pattern shows a category, not a single owner.\nLimitation: This impression is a class characteristic, not an individual one. Without unique wear marks, cuts, or embedded debris tied to one shoe, it can support other evidence but cannot prove which person left it.
This model shows the level of evidence and organization needed to complete: A claim-evidence-reasoning paragraph interpreting a team's forensic observations against reference characteristics, including at least one limitation of the evidence. Modeled on a shoe-impression comparison so it shows the format without answering today's fiber prompt.
- Write one defensible claim.
- Choose specific evidence that supports the claim.
- Explain the scientific rule that connects the evidence to the claim.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Upload your CER to the tracker or hand in the written copy by end of class.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Tap the speaker to hear a term. Add two of these to your notebook glossary with a definition and an example in your own words.
Pick just 2 or 3 words from today and make them yours: write what each one means in your own words, name the context clue or evidence that helped, then give one example from what you actually did in Analyze trace evidence. Try your own words first; the glossary is there if you get stuck. This is voluntary and counts as extra credit, so keep it short.
Saved on this device. Show Mr. Mendoza or add these to your notebook glossary to claim the extra credit.
Hand-picked readings and interactives for this lesson, from authoritative open organizations and PLTW's own public course outline.
Check yourself · commit, then reveal▸
Claim ceiling for this check: The supplied lesson evidence can support an observation, pattern, classroom mechanism, or next-step decision about Analyze . It cannot by itself prove causation, establish a real clinical diagnosis, or justify action outside this classroom task.
Your hair sample matches the suspect's hair color and thickness under the microscope. Write a claim about what this shows, and state its single biggest limitation.
Write an answer and pick a confidence to unlock the key.
Fast retrieval with instant answers, not the commit-then-reveal check above. Try each from memory first: write what you remember about the earlier units, then check yourself here.
Go further and get help▸
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
Today is individual work you can do from home: complete the same target above, then submit your CER.
Open the drop folderTurn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
Class still runs. Complete the online activity above (it's self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
Khan Academy: using the microscope (Cell biology)- CompleteEvery required part of the artifact is present, nothing left blank.
- AccurateThe science and the data are correct and match the evidence.
- Scientific reasoningYou explain your claim with evidence and reasoning (CER), not just an answer.
- Professional communicationClear, organized, labeled, and written the way a clinician or scientist would.
- SubmittedTurned in the right way, on the class site or handed to Mr. Mendoza in class, and confirmed. Not in Schoology: that is where the report-card grade appears later.