Characteristics of Microscopes
Since Robert Hooke first observed cork cells, micro-
scopes have unveiled the details of cell structure. These
powerful instruments provide biologists with insight into
how cells work—and ultimately how organisms function
Biologists use different microscopes depending on the
organisms they wish to study and the questions they want
to answer. Two common kinds of microscopes are light
microscopes and electron microscopes. In a
,light passes through one or more lenses to
produce an enlarged image of a specimen. An
forms an image of a specimen using a beam
of electrons rather than light.
An image produced by a microscope, such as the one
shown in Figure 1,is called a micrograph. Many micrographs are
labeled with the kind of microscope that produced the image—such
as a light micrograph (LM), a transmission electron micrograph
(TEM), or a scanning electron micrograph (SEM). Micrographs
often are labeled with the magnification value of the image.
is the quality of making an image appear larger than
its actual size. For example, a magnification value of 200indicates
that the object in the image appears 200 times larger than the
object’s actual size. is a measure of the clarity of an
image. Both high magnification and good resolution are needed to
view the details of extremely small objects clearly. As shown in
Figure 2,electron microscopes have much higher magnifying and
resolving powers than light microscopes.
Resolution
Magnification
microscope
electron
microscope
light
SECTION 1Looking at Cells 51
A red blood cell is about 5 times
longer than a bacterial cell.
A Lincoln penny is about 2,000
times longer than a red blood cell.
A human is about 100 times
longer than a Lincoln penny.
2 μm 2 cm 20 cm 2 m
Bacterium Blood cell Penny Hand Human
0.1 nm 1 nm 10 nm 100 nm 1 μm 10 μm 100 μm 1 mm 1 cm 10 cm 1 m 10 m
Electron microscopes
Sizes of objects
Light microscopes
Unaided eye
BacteriumBlood cell Penny
Hand Human
Sizes of Objects and Magnifying Power of Microscopes
10 μm
Magnification: 270
Figure 1 Micrograph.This
light micrograph (LM) shows
an amoeba.
Figure 2 Magnifying
power of microscopes.The
scale shows the size range of
objects that can be viewed
with electron microscopes and
light microscopes.