Page 13 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

Exam Tips Electron microscope
Remember the basic 1. Electron microscope is a microscope that uses beams of electrons to
principles of phase-contrast
microscope, transmission form an image.
and scanning electron
microscopes including 2. They are divided into transmission electron microscope and
examples of their uses. scanning electron microscope.
2 (a) Transmission electron microscope (TEM)
(i) It is a microscope that makes use of beams of electrons to
pass through a very thin section of an object to form an
image on a monitor screen.
2014
(ii) The principle involved is the same as the compound light
microscope in which the light is replaced by beams of
electrons; electromagnet is used instead of lens to focus
the beams of electrons as shown in Figure 2.6.

Electron
Light source
source

Electromagnetic
Condenser
lenses condenser
lens
Specimen Specimen

Objective
Objective
lens lens

Ocular Ocular
lens lens

Image
Image

Light microscope Electron microscope
Figure 2.6 Comparison of light and electron microscopes
(iii) Its uses are as follows:
• The limit of resolution is very small which is around 0.5
nm. Therefore, the structure of virus and ultrastructure
of cell including organelles can be studied.
• The final magnification produced in the form of
micrograph can be more than 250,000 times.
(iv) It has the following limitations:
• Experience is required to produce electro-micrograph of
cell structures.

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