A commonly used instrument to measure liquid volume is the
graduated cylinder. This instrument usually
measures liquid volume in milliliters (ml).
Using a Graduated Cylinder
It is important to remember to read to the bottom
of the curved line or meniscus when measuring
solutions involving water or most liquids. The
graduated cylinder at the left is divided into increments
of 2 ml, so the volume in it is 12 ml.
The graduated cylinder on the right is divided into
increments of 1 ml, so the volume in it is 16 ml.
The triple beam balance is commonly used to
measure mass in the biology lab. This device is named for its
three long beams on which sliding bars called riders (or
tares) are used to determine the mass of an object placed on
its platform. It is very important that the
riders on the rear beams are in the notch for the whole number
of grams and not in between notches. The front beam is a
sliding scale graduated in grams. The rider on this beam can
be positioned anywhere on the scale. Masses on a triple-beam
balance can be read to tenths of a gram and estimated to
hundredths of a gram.
Using the Triple Beam Balance
||The picture at the upper left
shows two different models of triple beam balances
commonly used in the biology laboratory.
The picture at the lower left shows the measurement of a
mass in progress. Without estimation,
the mass of the object appears to be 373.3 grams (g).
Most measurements in biology will involve metric units of
measurement. It is good to start at a whole number
increment that isn't 0. Many times the end of a
ruler will be worn away by student/teacher use or is
inaccurate due to the manufacturing process. It is
important to remember to take away the whole number increment
one has moved in on the ruler (in the example below 1 cm) from
the measurement obtained.
Using a Ruler to Measure Length
Problem: How long is leaf A?
The tip of the leaf is at about 6.5 cm, but note the
measurement started at 1 cm. Therefore, Leaf A
is 5.5 cm or 55 mm. in length.
The magnifying power of most objectives and oculars
is engraved on them. On the ocular, the marking can be found
on the top edge or on the smooth cylinder that fits inside the
body tube; on the objectives, magnification is on the side of
the cylinder. For example, a marking "10x" means
that the particular lens forms an image ten times larger than
the object being viewed. The total magnification of a
microscope is equal to the power of the eyepiece (ocular) X
power of the objective used. For example, if a
student is using a microscope with a 10 X ocular and a 43 X
high power objective, the total magnification of the specimen
the student is viewing is equal to 10 X 43 or 430 X (times).
Formula for Total Microscope
Power of the eyepiece
The size of a microscopic field of view can be determined
on low power using a device called an optical micrometer.
An economy version of this can be made by placing a clear
metric ruler on
the stage of a microscope and using it to estimate the field
of view. The light microscope is used to look at
cells or other similarly sized microscopic objects, so small
units of measure such as millimeters or micrometers are
used. It is important to remember that there are 1,000
micrometers in 1 mm (millimeter) and 1000 millimeters in a
Finding the Size of a Microscope
Field of View
In the pictured field of view at the left, it can be
observed that there are approximately 3 1/2 divisions
equal to a length of 3.5 mm. Therefore this
field of view is equal to 3.5 mm
or 3,500 micrometers.
Finding the Size of Multiple Cells in
a Field of View
The two cells in this field take up a field of view of
one millimeter. Therefore, the size of the specimen
is equal to 1 mm/2 cells or 0.5 mm per cell. There
is 500 micrometers in 0.5 mm., so the average size of each
cell is 500 micrometers.
Estimating Cell Size When the Field
of View is Known
It is often difficult to approximate the
approximate size of the field of view, but this ameba
considered lengthwise appears to occupy approximately 1/3
of the field of view. The field of view in the
left image is 3 mm. Given that the ameba in
the image takes up about 1/3 of that field, we can find
its approximate length by multiplying the 3 mm X 1/3
= 1 mm length or 1,000 micrometers for the approximate
length of this ameba.
The student is viewing the same ameba in the field of view
at the right on a higher power. The field of
view gets smaller which makes the ameba appear larger in