Difficulty: Beginner | Prerequisites: None. This is the first biology lab.
This lab introduces two foundational skills you will use in every biology lab going forward: working safely in the lab environment and using a micropipette to measure and transfer precise volumes of liquid. If you cannot pipette accurately, every experiment downstream (dilutions, PCR, gel loading) will produce unreliable results. The safety component covers personal protective equipment (PPE), chemical handling, and how to respond to common lab accidents. You do not need any prior lab experience for this material, but everything here is assumed knowledge for every lab that follows.
Always wear gloves, goggles, closed-toe shoes, and tie back long hair before entering the lab. Micropipettes measure tiny liquid volumes (microlitres) using a two-stop plunger system: press to the first stop to draw liquid in, then press through the second stop to expel it fully. Never dial a micropipette outside its printed range, or you will damage the instrument and ruin your measurements.
Micropipette (pipettor)
A precision instrument used to measure and transfer small volumes of liquid, typically in the microlitre (µL) range. Think of it as a very accurate, very small turkey baster with a dial for setting exact volumes.
First stop
The initial resistance point you feel when pressing the micropipette plunger down. Pressing to this point and then releasing draws liquid into the tip. In simple terms, this is where you stop pushing when you want to suck liquid up.
Second stop
The full depression of the plunger past the first stop. Pressing through the second stop forces all remaining liquid out of the tip. In simple terms, this is the extra push that clears the tip completely.
Microlitre (µL)
One millionth of a litre, or one thousandth of a millilitre. Think of it as a tiny fraction of a single drop of water. 1,000 µL = 1 mL.
P-20, P-200, P-1000
Common micropipette sizes named for their maximum volume in microlitres. A P-20 measures up to 20 µL, a P-200 up to 200 µL, and a P-1000 up to 1,000 µL (1 mL). In simple terms, the number tells you the biggest volume that pipette can handle.
PPE (Personal Protective Equipment)
Safety gear worn to protect against chemical splashes, biological hazards, and physical injury in the lab. For biology labs, this typically includes gloves, safety goggles, a lab apron, closed-toe shoes, and tied-back hair.
Microcentrifuge tube
A small plastic tube (typically 1.5 mL capacity) used to hold tiny volumes of liquid during experiments. Think of it as the standard "test tube" at the micro scale.
Parafilm
A flexible, waxy film used in labs to seal containers or as a clean surface to place liquid drops on for practice.
Good safety practices (PPE and behaviour)
Wear gloves at all times when handling chemicals or biological material. Gloves protect your skin from direct contact with irritants, corrosives, and pathogens.
Wear safety goggles to shield your eyes from splashes. Regular glasses are not a substitute.
Wear a lab apron to protect your clothing and skin from spills.
Wash your hands after removing gloves and before leaving the lab. This prevents you from carrying contaminants out of the lab environment.
Know where safety equipment is located: eye wash station, fire extinguisher, first aid kit, chemical spill kit.
Tie back long hair so it cannot fall into chemicals, flames, or equipment.
Wear closed-toe shoes. Open-toed shoes leave your feet exposed to dropped glassware and chemical spills.
Common unsafe behaviours to avoid
Leaning over open chemical containers. Fumes can irritate or damage your airways and eyes.
Throwing objects across the lab. This risks knocking over reagents or injuring others.
Removing goggles during an experiment. Your eyes have no protection against unexpected splashes.
Leaving items on the floor. Tripping hazards can cause serious spills.
Placing electronics near water or sinks. Water and electricity are a dangerous combination.
Handling biological hazards (e.g. E. coli)
Always wear gloves when transferring microorganisms between plates or tubes.
Remove and dispose of gloves before leaving the bench area. Put on a fresh pair when you return.
This prevents you from spreading live cultures to door handles, your phone, and other surfaces.
Responding to accidents
Chemical splash in eyes: go to the eye wash station immediately and flush for at least 15 minutes.
Prevention: wear your goggles at all times. Most eye injuries in the lab are entirely preventable.
Hair or clothing catches fire or contacts chemicals: the incident is usually caused by loose hair or improper attire. Tying hair back and wearing closed-toe shoes and an apron prevents the majority of these accidents.
Choosing the right pipette
Each micropipette has a stated volume range printed on it. Use the pipette whose range covers the volume you need.
For 25 µL: use a P-200 (or P-100, depending on your lab's inventory).
For 50 µL: use a P-200.
For 900 µL: use a P-1000.
Never dial a micropipette above or below its stated range. Doing so damages the internal mechanism and makes all future measurements unreliable.
Proper pipetting steps
Attach the correct size disposable tip to the pipette.
Set the desired volume using the dial.
Depress the plunger to the first stop (you will feel a distinct resistance).
While holding at the first stop, immerse the tip in your liquid.
Release the plunger slowly and smoothly. Releasing too quickly introduces air bubbles.
Move the tip to your target container.
Depress the plunger slowly to the first stop to dispense the liquid.
Continue pressing through the second stop to expel the last traces of liquid from the tip.
Release the plunger slowly, allowing it to return all the way out.
Comparing drop sizes
Pipette 25 µL of water onto Parafilm. Then pipette 50 µL beside it (not touching). The 50 µL drop should be visibly larger, roughly twice the size.
Merge the two drops by dragging the pipette tip from the 25 µL drop into the 50 µL drop. The combined volume is 75 µL.
Set the pipette to 75 µL and draw up the merged drop. If your technique is correct, you should be able to draw up the entire volume with little to no air space at the end of the tip.
Why this matters
This exercise trains your muscle memory for the two-stop system and helps you judge whether your volumes are accurate by visual comparison before moving on to real experiments.
Micropipetting is the backbone of molecular biology, clinical diagnostics, and pharmaceutical research. Every time a lab runs a COVID test (PCR), loads a DNA gel, or prepares a drug formulation, someone is pipetting precise microlitre volumes. Sloppy pipetting in a clinical lab can mean a false negative on a patient's test. In an industrial lab, it can mean a batch of medication with the wrong concentration.
Students often think regular prescription glasses count as eye protection. They do not. Safety goggles wrap around the sides and top to block splashes from every angle.
Students sometimes release the plunger quickly when drawing up liquid. This pulls air into the tip and gives you less liquid than you set on the dial. Always release slowly.
Students assume that if a pipette can physically be dialled past its range, it is fine to use at that setting. It is not. The mechanism is not calibrated outside its stated range, and forcing it causes permanent damage.
Students occasionally reuse the same gloves after leaving the lab bench (going to the bathroom, checking their phone, then returning). Contamination spreads this way. Remove gloves when you leave the bench, dispose of them, and put on fresh ones when you return.
⚠️ Know which pipette size (P-20, P-200, P-1000) to use for a given volume. Expect a question asking you to pick the correct pipette for a stated volume.
⚠️ Be able to describe the two-stop plunger system: first stop draws liquid in, second stop expels it completely.
⚠️ Understand why you must never dial a micropipette outside its stated range.
⚠️ Know the five essential PPE items for a biology lab: gloves, goggles, apron, closed-toe shoes, hair tied back.
⚠️ Be prepared to identify safe and unsafe practices from a lab photo or scenario description.
True or False: You should release the micropipette plunger as quickly as possible when drawing up liquid. (False. Release slowly to avoid air bubbles.)
True or False: A P-200 can accurately measure 250 µL. (False. 250 µL exceeds its maximum range of 200 µL.)
Fill in the blank: The ______ stop draws liquid into the tip, and the ______ stop expels the last traces. (first; second)
True or False: Prescription glasses are an acceptable substitute for safety goggles. (False. They do not protect from side or top splashes.)
Fill in the blank: 1,000 µL = ______ mL. (1 mL)
Q: You need to transfer 150 µL of a solution. Which micropipette should you use, and why?
A: Use a P-200. Its range covers 20 to 200 µL, so 150 µL falls comfortably within it. A P-1000 would work but is less accurate at such a small fraction of its range. A P-20 cannot reach 150 µL.
Q: Describe the correct sequence for expelling liquid from a micropipette tip.
A: Press the plunger slowly to the first stop to dispense the bulk of the liquid. Then continue pressing through the second stop to push out the remaining liquid. Release the plunger slowly and smoothly.
Q: A student in your lab is not wearing goggles, has their hair down, and is wearing open-toed sandals. List three safety violations and explain the risk of each.
A: (1) No goggles: eyes are exposed to chemical splashes. (2) Hair not tied back: hair could dip into chemicals or catch on equipment. (3) Open-toed shoes: feet are unprotected from dropped glassware or chemical spills.
Q: Your lab partner leaves the bench while wearing gloves and returns still wearing them. Why is this a problem?
A: The gloves may have contacted biological material or chemicals at the bench. By wearing them outside the work area, the student spreads contaminants to door handles, personal belongings, and other surfaces. Gloves should be removed and disposed of before leaving the bench, and a fresh pair put on when returning.
Q: What happens if you dial a P-200 to 250 µL?
A: The pipette is being used outside its calibrated range. The volume it delivers will be inaccurate, and the internal piston mechanism may be damaged, making the pipette unreliable even within its proper range afterward.
Accurate pipetting is the mechanical prerequisite for serial dilutions (covered in the companion study notes). Every dilution calculation assumes you transferred exactly the volume you intended. Lab safety principles introduced here apply identically in microbiology, chemistry, and anatomy labs, so this material carries across the entire science curriculum.
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