Biological Principles
Lab: Scientific Measurements
Name: ________________________________
PURPOSE
 To become familiar with the reference units and prefixes in the metric system.
 To become familiar with some common laboratory equipment.
INTRODUCTION
Biology students, as part of their laboratory experience, will be asked to make observations.
Observations may be either qualitative or quantitative. A qualitative observation describes a
characteristic and is not numerical; a quantitative observation is numerical. Scientific observations are
usually made as quantitative as possible so that they are easier to evaluate. For example, if you were
trying to find the insect with the world's largest wingspan, quantitative observations are needed. An
insect's wingspan may be qualitatively described as huge, but a quantitative description of an insect’s
wing span as 20 centimeters would be much more useful for this project.
The metric system is universally used in science because it is a decimal system of measurement and
is easy to convert from one unit of related measurement to another (e.g., volume to mass). The metric
reference units are the meter (m) for length, the liter (l) for volume, and the gram (g) for mass. Prefixes
are used as part of a unit to indicate a portion of or a multiple of a reference unit. For example, the prefix
milli (m) indicates .001 (1/1000). A millimeter (mm) is 0.001 (1/1000) of a meter. A milliliter (ml) is 0.001 (1/1000)
of a liter. A milligram (mg) is 0.001 (1/1000) of a gram. Note that the same prefixes are used throughout the
metric system, regardless of whether we’re discussing length, volume or mass.
The table below lists the prefixes we will be using most often in this course.
Prefixes of the Metric System
Prefix
kilo
centi
milli
micro
nano
Abbrev.
k
c
m
µ
n
MATERIALS
 metric ruler
 microscope slide
 10-ml graduated cylinder
 100-ml graduated cylinder
 ungraduated pipette (dropper)
 weigh boat
 sand dollar
 tap water
Part of Reference Unit
1000
1
/100
or
0.01
1
/1000
or
0.001
1
/1,000,000
or
0.000001
1
/1,000,000,000
or
0.000000001







or
or
or
or
or
103
10-2
10-3
10-6
10-9
1-ml pipette
10-ml pipette
green pipette pump
blue pipette pump
digital balance
pinecone
dollar bill
1
PROCEDURE
A. Length
Length is the measurement of a line from end to end. The reference unit of length is the meter (m).
Here is an example of a ruler with a metric scale:
1 cm


The numbered lines count off the centimeters (cm).
The unnumbered lines count off the millimeters (mm).
Answer the following questions.
How many millimeters are there in a centimeter?
___________
How many centimeters are there in a meter?
___________
Which is larger, a millimeter or a centimeter?
__________________
Estimating and visualizing lengths is a useful skill when reading and making observations.
Using the metric scale of the ruler provided, find some part of your hand that is 1 cm long.
What part of your hand did you measure?
_________________________
Find some part of your hand that is 10 cm long.
What part of your hand did you measure?
_________________________
Do the following work to gain an ability to visualize lengths in the metric system.
First, estimate the measurement of the first item on the list using only your eyes and hands but no
rulers. Record your estimate, including units. Second, actually measure the item with your ruler and
record your measurement, including units. How well does your estimate compare to the actual
measurement? Continue in the same way with each item on the list.
Estimate
Actual Measurement
Length of your pinecone
_____________
_____________
Diameter of your sand dollar
_____________
_____________
Diameter of this letter "e"
_____________
_____________
Width of a microscope slide
_____________
_____________
Length of a microscope slide
_____________
_____________
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2
B. Volume
Volume is the space that a given object occupies. The reference unit of volume is the liter (l).
beakers
graduated
cylinders
Erlenmeyer
flasks
Graduated cylinders and graduated pipettes are measuring instruments. Beakers, flasks and droppers are
not accurate enough for measuring, so they are used primarily for moving, mixing or storing.
Answer the following questions.
1.4 L
=
__________ ml
0.2 L
=
__________ ml
550 ml
=
__________ L
Pour some water into a 100-ml graduated cylinder. Observe the curved surface of the water. This is called
the meniscus. The conventional reading of the volume in the graduated cylinder is taken by looking at
the lowest point of the meniscus.
Use an ungraduated pipette (dropper) to find out how many drops there are in 1 ml of water. Count the
number of drops needed to fill a 10-ml graduated cylinder to the 1 ml mark.
There are approximately ______________ drops in 1 ml.
Pipette Pumps: Pipettes are hollow glass tubes that are marked (or graduated) and allow for precise
measurements of volume. Liquids are moved through pipettes using devices called pipette pumps. Use
the blue pipette pump with the 1 ml graduated pipette. Use the green pipette with the 10 ml pipette. Very
gently push the pump onto the top of the pipette. Make sure that the white plunger on the top of the
pipette is pushed down completely.
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3
Fill the 10-ml pipette to the 10-ml mark with water and dispense the water into the 10-ml graduated
cylinder.
Determine the volume of water in the graduated cylinder. Remember to look for the bottom of the
meniscus. _________________________________
Does the water come exactly to the 10 ml mark on the graduated cylinder?
___________
If you don't have exactly 10 ml of water in the graduated cylinder, what might account for the
discrepancy?
______________________________________________________________________________
______________________________________________________________________________
Use the 1-ml graduated pipette to dispense 0.4 ml water on the table.
Measure the diameter of the drop of water to the nearest mm. _____________
Which do you think would be more accurate for measuring 0.8 ml water, a graduated cylinder or a
graduated pipette? _____________________________________
From the instruments that you have used in this lab, indicate which instrument you would use and the
best size of that instrument to choose.
To Measure
Instrument
Size
50 ml water
______________
______________
4.2 ml water
______________
______________
15 ml water
______________
______________
0.4 ml water
______________
______________
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4
C. Mass
The metric reference unit for mass (weight) is the gram (g).
Using the digital balance, weigh each item and record your measurement, including units. Make sure
you set the balance to 0 grams before each measurement. This is accomplished by pushing the button
marked TARE until the balance is zeroed.
Mass of pinecone
___________
Mass of sand dollar
___________
Mass of dollar bill
___________
Which weighs more, the sand dollar or the real dollar?
______________________
How much more?
______________________
How much would 1,000 dollar bills weigh?
______________________
How much do you think a $1,000 bill would weigh?
______________________
Place a weigh boat on the digital balance and press the TARE button. Again, this will set the balance to
zero, taking into account the weight of the weigh boat.
Add 20 ml of water to the weigh boat (while it is still on the balance).
Mass of 20 ml of water
___________
Dump out the water and repeat the procedure with the following volumes of water.
8 ml
___________
78 ml
___________
60 ml
___________
45 ml
___________
Graph your five data points as a line graph on the grid supplied. Your independent variable (the volume)
should go on the X-axis (horizontal axis); the dependent variable (the mass) should go on the Y-axis.
Make sure you label the axes correctly!
Based on your graph, how much does 50 ml of water weigh?
___________
CLEAN UP
 Empty any tap water in the sink.
 Return your materials to the instructor’s bench.
 Wipe down your lab bench with cleanser and paper towels.
 Push in your chair when you leave.
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6