Biology Foundations and Lab Skills Teaching Resources · High school biology; AP extensions where noted.
Practice using metric tools before a biology investigation. Students record what an instrument supports, compare repeated readings, and explain uncertainty. The kilogram is the SI base unit of mass; grams are convenient for many classroom measurements. A milliliter is a commonly used volume unit, and 1 mL equals 1 cm³.
Objectives, prerequisites, and materials
Students will read scales with units, distinguish mass from volume, calculate displaced volume, and avoid unsupported digits. Prerequisites: decimals and subtraction. Materials per group: a millimeter-marked ruler, teacher-approved small solid rectangular object, water, a suitable graduated cylinder, a balance, a tray, a dropper, and one clean, nonporous sinking object that fits the cylinder safely.
Preparation and safety: the teacher checks instrument ranges, condition, required protection, and cleanup. Use room-temperature water, no tasting, and no mouth-pipetting. Keep water away from electrical equipment, clean spills promptly, and lower objects gently rather than dropping them into glass. An accessible teacher demonstration or supplied data may replace any station.
Station 1: length and calculated volume
- Check the ruler’s smallest markings and its zero point.
- Measure the object’s length, width, and height in centimeters, recording precision consistent with the ruler and the teacher’s measurement convention.
- Calculate volume = length × width × height. Report cubic centimeters and avoid extra digits that suggest more precision than your measurements support.
Station 2: liquid volume and displacement
- Place the cylinder upright on a level surface. For water, read the bottom of its meniscus at eye level.
- Record the initial water volume, then gently immerse the selected object fully. Avoid trapped bubbles and overflow.
- Record the final volume. Subtract initial from final to find the object’s volume. If an object floats, dissolves, absorbs water, or reacts, this simple method is unsuitable.
Station 3: mass
- Follow the balance’s instructions for zeroing or taring.
- Measure a dry object within the instrument’s capacity. Include grams and record the displayed reading appropriately.
- Remove and replace it for repeat readings. Discuss instrument resolution and possible causes of variation. Repeated readings of one object are not independent samples of a population.
Optional station: drop size
Using the same dropper and technique, count drops while the measured water volume rises by 1 mL. Repeat three times and calculate the mean count. Drop size varies with the dropper, liquid, and technique; a drop is not a universal metric volume unit.
| Station | Raw measurements, with units | Calculation or comparison | One limitation |
|---|---|---|---|
| Length | Record three dimensions | Calculate cm³ | State ruler resolution |
| Displacement | Initial and final mL | Final − initial | Note bubbles or reading angle |
| Mass | Three readings in g | Compare readings | State balance resolution |
Check your reasoning
Example: 18.0 mL initially and 22.5 mL finally give 4.5 mL displaced, equivalent to 4.5 cm³. This does not determine mass without another measurement. Question: Does a calculator’s long decimal display make a measurement more precise? No; precision depends on the measurements and method, not the number of displayed digits.
Legacy notebook copy
Download the legacy metric lab (Word). It includes drop counting, displacement, balance work, box volume, and colored-water transfers. If assigning it, correct its claim that the gram is the SI base unit and its instruction to round all calculated volumes to two decimal places. Check equipment capacity, local safety instructions, and layout first. The on-page stations above are the revised teaching sequence.