Microscopy

Topics: Scanning electron microscope, Electron microscope, Electron Pages: 16 (406 words) Published: June 20, 2015
Microscopy
Cell are very Small








Metabolic requirements set upper limits on the size
of cells
The surface area to volume ratio of a cell is critical

As the surface area increases by a factor of n2, the
volume increases by a factor of n3
Small cells have a greater surface area relative to
volume

Figure 6.7

Surface area increases while
total volume remains constant

5
1
1
Total surface area
[sum of the surface areas
(height  width) of all box
sides  number of boxes]

6

150

750

Total volume
[height  width  length
 number of boxes]

1

125

125

Surface-to-volume
(S-to-V) ratio
[surface area  volume]

6

1.2

6

Microscopy


Scientists use microscopes
to visualize cells – too small
to see with the naked eye



Two types of microscope:


Light Microscope (LM)



Electron Microscope
 Scanning Electron
Microscope (SEM)
 Transmission Electron
Microscope (TEM)

Microscopy




In light microscope, visible light
is passed through a specimen
and then through glass lenses
Lenses refract (bend) the light so
that the image is magnified



Three important parameters of
microscopy:






Magnification – the ratio of
an object’s image size to its
real size
Resolution – the measure of
the clarity of the image, or
the minimum distance of two
distinguishable points
Contrast – visible differences
in parts of the sample

Microscopy




LMs can magnify
effectively to about 1,000
times the size of the actual
specimen
Most subcellular structures,
including organelles are
too small to be resolved by
an LM

Microscopy


Various techniques has
been used to enhance
contrast and enable cell
components to be stained
or labeled



Recent advances in light
microscopy:




Confocal microscopy and
deconvolution microscopy
provide sharper images of
three-dimensional tissues
and cells
New techniques for labeling
cells improve resolution

Figure 6.3a

50 m

Brightfield
(unstained specimen)

Figure 6.3b

Brightfield
(stained specimen)

Figure 6.3c

Phase-contrast

Figure 6.3d

Differential-interferencecontrast (Nomarski)

Figure 6.3e

Fluorescence

10 m

Figure 6.3f

50 m

Confocal

Figure 6.3g

10 m

Deconvolution

Figure 6.3h

1 m

Super-resolution

Microscopy




There are two basic types
of electron microscopes
(EMs) used to study
subcellular structures
Scanning electron
microscopes (SEMs):




focus a beam of electrons
onto the surface of a
specimen
providing images that look
3-D



Transmission electron
microscopes (TEMs):


Focus a beam of electrons
through a specimen



mainly to study the
internal structure of
cells

SEM & TEM
Longitudinal section
of cilium

Cilia

2 m
Scanning electron
microscopy (SEM)

Cross section
of cilium

2 m
Transmission electron
microscopy (TEM)

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