Micropipetting and aseptic technique
This page has four parts, in the order you use them. Part 1 is what you need to know. Part 2 says what to do, in plain English. Part 3 shows the work done once on a case that is not yours. Part 4 is your own work and where to turn it in.
Open your materials, follow the steps, then turn in your work.
Practise setting and using a micropipette, and explain why aseptic technique changes the number you get.
Optional: listen or watch a unit review▸
Part 1 of 4 · Background and definitions▸
💡 Big idea: A pipetting error does not announce itself: it becomes a number that looks fine and is wrong, which is why technique is the measurement.
- • A delivers only volumes inside its printed range; a setting outside the range damages it and moves the wrong volume.
- • The plunger has two stops: the first stop measures the volume you draw in, and the second stop pushes out the last drop when you deliver.
- • keeps other samples and microbes out of yours: a fresh tip for every sample, lids closed, and a clean bench.
Biodiversity is the search space, so an argument about patents is also an argument about what gets searched and by whom.
A pipetting error does not announce itself: it becomes a number that looks fine and is wrong, which is why technique is the measurement.
Driving question: You set a volume and press the plunger. From the receiving tube alone, how would you know whether the volume you set is the volume that actually went in?
What you already know: Biodiversity is the search space, so an argument about patents is also an argument about what gets searched and by whom.
New idea: A pipetting error does not announce itself: it becomes a number that looks fine and is wrong, which is why technique is the measurement.
Visual or model: No figure is attached to this lesson. The readings, the worked example and E1 to E3 carry the evidence.
- Observe or measure the relevant feature in today's lesson.
- Organize the observation with a stable evidence ID.
- Apply this rule: Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: You set a volume and press the plunger. From the receiving tube alone, how would you know whether the volume you set is the volume that actually went in?
What the evidence supports: E1 to E3 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.
- • innovation: A new idea, method, or product that improves on what came before and creates real value for people.
- • stakeholder: Any person or group affected by a project or decision, such as users, patients, families, or the team building a solution.
- • limitation: A weakness or boundary of a study, design, or method that restricts how far its results can be trusted or applied.
- • claim: The position you are defending, stated in one clean sentence; if you cannot say it simply, you do not have it yet.
- • evidence: The facts, data, and cases that carry your claim. Opinions are free; evidence costs homework.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice. This is thinking practice for the one turn-in named under Turn in, not a second submission.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
Laboratory depends on matching each identified hazard to an appropriate containment practice, protective measure, and stop-work condition before the procedure begins.
Limit: The lesson check does not replace the site-specific SDS, approved procedure, teacher supervision, or emergency plan.
Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
Limit: A well-organized classroom study can still be limited by , measurement quality, confounding, and the population represented.
Demonstrate the two-stop plunger without prompting.
Limit: E3 defines the classroom product or success criterion. It is not independent scientific evidence and cannot justify a clinical or causal claim.
Today's decision · Simulated classroom evidence scenario
Your role: biomedical team member
Decision: Your team must decide what the evidence from today's lesson supports before submitting the notebook record named on today's page.
- • Repeat the transfer until the two-stop motion is consistent, because an unpracticed plunger stop produces a number that still looks normal.
- • Move on once the volume is dialed correctly, since the setting you chose is the amount the pipette will deliver.
- • Hold your volume claim until a repeated transfer shows the same result, since one clean-looking reading cannot tell technique from luck.
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Use it inside the one turn-in named under Turn in; it is not a separate submission.
Claim ceiling: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
Students often think a contaminated sample will fail visibly, so if the reaction runs and the reading lands in a , the technique must have been fine. The trap: does not stop the chemistry. A trace of the previous sample rides in on a reused tip, the reaction develops normally, and the result lands somewhere believable. In range is not the same as correct, which is why the control is a fresh tip at the bench rather than a check on the numbers afterwards.
- 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.
Part 2 of 4 · Directions in plain English▸
2.1 Open your materials
Use the materials named in the first step below. Open lesson resources.
2.2 Start the work
Read the micropipette care resource and record the volume range of the pipette you were issued.
Show all 5 required steps
- Read the micropipette care resource and record the volume range of the pipette you were issued.
- Set a volume, seat a tip, and practise the two-stop plunger until the motion is consistent. The plunger has two stops: press to the FIRST stop to draw liquid in, and press past it to the SECOND stop to push the last drop out.
- Practise transferring a fixed volume and describe what a wrong first stop does to it.
- Label every tube before any liquid moves.
- Write why a contaminated sample produces a wrong result rather than no result.
Lost your place? Look at your rack. If every tube in front of you is labelled, pick up at the transfer step. If any tube is unlabelled, stop and label the whole rack before another drop moves, because a tube you name from memory is a tube you are guessing at.
- 0-5 minWarm-up: write the two stops of the plunger in order.
- 5-20 minRead the care resource; record the volume range of the pipette you were issued.
- 20-45 minSet a volume, seat a tip, and practise the two-stop plunger with water until the motion is the same every time.
- 45-60 minLabel your tubes, transfer a fixed volume into each, and describe what a wrong first stop does to it.
- 60-72 minWrite why a contaminated sample gives a wrong result rather than no result.
- 72-80 minExit check: show a partner the two-stop motion without prompting; clean up.
- • This is the last lesson of the fall term, and it is a technique day: the is how later biotech labs measure small volumes.
- • A pipetting error does not announce itself. It becomes a number that looks fine and is wrong.
- • Handling and preparing materials is part of your end-of-course WebXam, and a is the tool for small volumes.
- • Label every tube before any liquid moves.
PLTW connection and today's work
Open myPLTW and go to Lesson 4.2 New Frontiers, Activity 4.2.2 Under the Sea, and review the micropipette care resource before the lab.
Today's stopping point: Your bioprospecting exit ticket was due last class. Today record your pipette's range, practise the plunger until it is consistent, and finish the notes before the period ends.
PLTW activity titles identify the course connection. If your account will not open, use the posted materials for today and tell Mr. Mendoza. Do not mark an online activity complete unless you completed it.
Use the turn-in directions in Part 4 of this page. Do not create a second submission unless your teacher asks for one.
Show another explanation or a smaller first step
Need help? Choose a starting point
Finish the assigned lab safely before starting extra practice.
Part 3 of 4 · Worked example▸
This is a parallel case, not your own. Read it for the order of the work, then do your own in Part 4.
The pipette I was issued: a variable P100, range 10 to 100 microliters. I wrote the range down first, because setting 5 or 150 on this barrel is outside what it can deliver, and forcing the dial past its stop damages it.
Setting the volume: I turned the dial down to 50 and read the display as 0 5 0, which on this model is 50 microliters. My partner read it back to me before I drew anything.
Seating a tip: press the shaft straight down into the tip in the box, one firm push. A tip on crooked leaks air, and a leak means the volume in the tip is not the volume on the dial.
The two-stop plunger, in order:
- 1. Press down to the FIRST stop before the tip goes anywhere near the liquid.
- 2. Put the tip just under the surface and release slowly to draw the set volume.
- 3. Move to the receiving tube and touch the tip to the tube wall.
- 4. Press to the first stop to deliver, then to the SECOND stop to push out what is left in the tip.
- 5. Eject the tip. Do not let the plunger back up while the tip is still in liquid, or the sample gets sucked back.
What a wrong first stop does: if I press past the first stop before drawing, I blow out extra air and pull up more than 50 microliters. Nothing about that looks wrong. The tube fills, the run finishes, and the number at the end is simply too high.
Labeling rule I wrote for myself: every tube gets labeled before any liquid moves, on the side and on the cap, because caps get swapped while a rack sits open. A tube I label afterwards is a tube I am labeling from memory.
Why contamination is worse than an obvious failure: if I reuse a tip between samples, a little of sample 1 rides into sample 2. Sample 2 still develops, the reading still lands in a believable range, and there is nothing in the number itself that tells me it is wrong. A dropped tube announces that it failed. A shared tip does not. That is why the tip changes between every sample and the bench gets wiped before I start.
| Step | Plunger position | What is happening |
|---|---|---|
| 1 | First stop | Air pushed out before the tip enters the liquid |
| 2 | Released slowly | The set volume is drawn into the tip |
| 3 | First stop | The set volume is delivered into the receiving tube |
| 4 | Second stop | Residual liquid is pushed out of the tip |
| 5 | Eject | Tip discarded before the next sample is touched |
This model shows the level of evidence and organization needed to complete: Completes the technique note-taking task: the issued pipette's volume range, the two-stop plunger written out in order, what a wrong first stop does to a transfer, the labeling rule, and why contamination produces a believable wrong number.
- Date and label the entry.
- Record the procedure, observation, or design decision clearly.
- End with what the evidence means and the next step.
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: Keep the notes in your science notebook as part of your Unit 4 record.
A research team lays out its question, variables, controls, sampling plan, measurement record, and analysis before deciding what the data support.
- Which variable is changed or compared?
- Which conditions and measurements must stay consistent?
- Which conclusion is inside the study's evidence boundary?
Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
A well-organized classroom study can still be limited by , measurement quality, confounding, and the population represented.
- • Question and variable cards map to the study design.
- • Control and measurement cards map to fair, reproducible data collection.
- • The conclusion card maps to a bounded claim supported by the analysis.
Part 4 of 4 · Your work▸
Check your work before submitting
- Demonstrate the two-stop plunger without prompting.
- Explain contamination as a source of a plausible wrong number, not an obvious failure.
Before lab work: read the safety rules
- Goggles on for the whole practice.
- Never pipette by mouth; the micropipette is the only way liquid moves today.
- Keep the pipette upright whenever a tip is on it, and never lay it down with liquid in the tip, because liquid runs back into the barrel.
- Eject every used tip into the tip waste container, never the classroom bin, and do not touch tips with your fingers.
- Wipe up any spill at once with a paper towel and tell Mr. Mendoza; wipe down the bench before and after.
- Wash your hands at the end.
4.1 Turn in your work
DueCheck the Schoology assignment for this day- Hand in
- Micropipetting notes: your pipette's volume range, the two-stop plunger written out in order, what a wrong first stop does to a transfer, your tube-labeling rule, and why a contaminated sample gives a wrong result rather than no result.
How to submit and name your file
Keep the notes in your science notebook as part of your Unit 4 record.
In Schoology, open your course and the assignment for this lesson. Attach your file, select Submit, and check that it appears in the submission.
PDF upload helpYou get two school days for every day you were absent, so this deadline moves with you.
Find this lesson's Schoology assignments
These are existing assignments for your section. Follow the directions in the assignment you are working on; this list does not add new work. A PLTW Work row repeats on every day of its lesson; submit it once. Check Schoology for each deadline.
- Extra Credit · due Fri 12/18 · Wk17 · Design a mobile medical facility and prove it works (up to 20 points added)(optional extra credit: it can add points, never lower a grade)
Link will not open? Open Schoology, choose your course and section, and find the title shown above.
- 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.
- SubmittedGo to Schoology to turn this in. Submit one PDF. Schoology attaches your name to your upload; on the page itself, write your period and code. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf. If you cannot get in, see Mr. Mendoza. Do not skip the work.
- Error analysis and method · counts doubleName a specific limit of the method and how it moved your result, and compare what you predicted to what happened. "Human error" does not count; say what about the procedure or instrument caused it.
How this lesson connects
Keep using what you learned last class: Biodiversity is the search space, so an argument about patents is also an argument about what gets searched and by whom. Today: A pipetting error does not announce itself: it becomes a number that looks fine and is wrong, which is why technique is the measurement.
Practice: try a question, then check your answer▸
Claim ceiling for this check: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
You set the same volume for every transfer, but on the third tube your thumb went past the first stop before the tip entered the liquid. You noticed, and tube three looks exactly like the other four. Commit to an answer first: what is now true about tube three, and what should you do about it?
Write an answer and pick a confidence to unlock the key.
Missed class or ready for more?▸
Run this before you touch the bench. It is built from the real lab procedure, so the decisions you make here are the ones you will make with the equipment in your hands.
I can name the procedure's purpose and the evidence I will record. I can state today's specific hazards and the control for each. If this deck does not name them, I ask Mr. Mendoza before I touch anything. My data table is ready before materials are handled.
Finish the checklist before you handle any material.
- • Goggles on for the whole practice.
- • Never pipette by mouth; the micropipette is the only way liquid moves today.
- • Keep the pipette upright whenever a tip is on it, and never lay it down with liquid in the tip, because liquid runs back into the barrel.
- • Eject every used tip into the tip waste container, never the classroom bin, and do not touch tips with your fingers.
- • Wipe up any spill at once with a paper towel and tell Mr. Mendoza; wipe down the bench before and after.
- • Wash your hands at the end.
- 1Before materials are handled, identify the purpose, variables or comparison, controls, measurement units, and stop-work condition.
- 2Read the micropipette care resource and record the volume range of the pipette you were issued.
- 3Set a volume, seat a tip, and practise the two-stop plunger until the motion is consistent. The plunger has two stops: press to the FIRST stop to draw liquid in, and press past it to the SECOND stop to push the last drop out.
- 4Practise transferring a fixed volume and describe what a wrong first stop does to it.
- 5Label every tube before any liquid moves.
- 6Write why a contaminated sample produces a wrong result rather than no result.
- 7Record each result in the prepared table before interpreting it. Mark missing, repeated, or invalid results truthfully.
- 8Complete the named cleanup and waste route, remove PPE safely, wash hands when required, and confirm the station is ready for the next group.
| Which trial or sample this row is | What you changed on purpose | What you measured, with units | What you saw, before you explain it | Anything that could make this reading wrong |
|---|---|---|---|---|
Before the procedure, predict the result and cite the rule behind the prediction.
After the procedure, compare the result with the prediction and name one limitation or source of uncertainty.
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.
The bench work needs equipment you do not have at home. Do the thinking half now: read the procedure, write your prediction, and set up your data table so it is ready.
Back in class. Ask Mr. Mendoza for the class data set, or for a bench slot to run it yourself. Do not submit a Notebook check with invented numbers.
Class still runs. Complete today's work as this page describes (it is self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
NIBIB: biomedical engineering science topics and new frontiersThe optional extra-credit track is open. Complete reserved-unit work from home, including virtual labs, for extra credit. Each item shows its correct submission route.
Open the extra-credit trackSources: slides, readings, and resources▸
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.
Hand-picked readings and interactives for this lesson, from authoritative open organizations and PLTW's own public course outline.
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