Biology (Holt)

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.