Different types
of microscopes
© OCR 2016
Objectives
Learners should be able to:
• explain how an electron microscope is different
to a light microscope
• define the terms magnification and resolution
• convert units of measurement used in
microscopy
• state with examples, when different microscopes
are used.
© OCR 2016
What is the smallest thing you can see with
your eyes?
What is the smallest thing you can see with a
light microscope?
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Light Microscopes
Eyepiece
lens
Light rays are
focussed using glass
lenses to magnify
objects up to x1500
Coarse and fine Focusing
Objective lenses
Stage
Stage clips
Diaphragm
Mirror
© OCR 2016
Cheek cell
plasma membrane
cytoplasm
© OCR 2016
nucleus
Onion cells
© OCR 2016
To see more detail an electron
microscope can be used
• Electron microscopes use an electron beam
instead of light, which is focussed using
electromagnets.
• The specimen has to be specially prepared and
held inside a vacuum chamber from which the air
has been pumped out (because electrons do not
travel very far in air).
• The image is formed as a photograph (called
an electron micrograph) or as an image on a TV
screen.
© OCR 2016
Electron microscope
high voltage
electron gun
anode
condenser lens
objective
aperture lens
Intermediate
lens
specimen
projector lens
fluorescent
screen
© OCR 2016
• Specimen is dead
and dehydrated.
• Black and white
image [or false
colour].
• Objects can be
magnified up to
x500 000!
Which parts of this cell would be
visible using a light microscope?
•
•
•
•
© OCR 2016
Nucleus
Cytoplasm
Cell membrane
Possibly mitochondria
Which parts of the cell would be visible using
an transmission electron microscope (TEM)
•
•
•
•
© OCR 2016
Nucleus
Cytoplasm
Cell membrane
Possibly mitochondria
What can be seen with an electron
Microscope?
© OCR 2016
Scanning electron microscope
Work in a similar way but are designed to make
images of the surfaces of objects.
© OCR 2016
Resolution
• Resolution means how close together 2 objects
can be, and still be seen as separate objects.
• Resolution of a light microscope 0.250 µm
• Resolution of an electron microscope 0.25 nm
• Do you know how small µm and nm are?
© OCR 2016
Magnification
• Magnification is how many times bigger an
object is in an image, than in real life.
• Magnification using light microscope – up to
x1500
• Magnification using an electron icroscope – up
to x500 000
© OCR 2016
Comparing light and electron microscopes
Light microscope
Magnification
Resolution
Type of radiation used
Focussed by
Type of material that can
be viewed
Size
Preparation and cost of
material
© OCR 2016
Electron microscope
Comparing light and electron microscopes
Light microscope
Electron microscope
Magnification
x1500
X500,000
Resolution
250nm
0.25nm
Type of radiation used
Light
Electrons
Focussed by
Glass lenses
Electromagnets
Type of material that can
be viewed
Living/moving/dead/abiotic
Dead/abiotic
Size
Small and portable
Large and static
Preparation and cost of
material
Cheap and easy
Difficult and expensive
© OCR 2016
How big are cells?
Units for measurements
• mm
• Micrometers - µm
• Nanometers – nm
• 1mm = 1000µm
• 1µm = 1000nm
© OCR 2016
Cheek cell
• Approximately 60µm in diameter.
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Onion cell
• Approximately
200µm in length.
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Mitochondrion
• Approximately 2µm in
diameter.
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HIV Virus
• Approximately 2µm
in diameter.
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Put these in size order starting with
the biggest
•
•
•
•
•
•
•
•
•
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Cilia 10µm
Mitochondrion 2µm
Sperm cell 55µm
Ribosome 20nm
Human kidney 13cm
Nerve cell from a giraffes neck 3m
Red blood cell 9µm
HIV virus 100nm
Human egg 100µm
Put these in size order starting with
the biggest - answers
•
•
•
•
•
•
•
•
•
© OCR 2016
Nerve cell from a giraffes neck 3m
Human kidney 13cm
Human egg 100µm
Sperm cell 55µm
Cilia 10µm
Red blood cell 9µm
Mitochondrion 2µm
HIV virus 100nm
Ribosome 20nm
Convert these measurements
1.
2.
3.
4.
5.
6.
© OCR 2016
10mm =
3mm =
670 µm =
0.75mm =
24 µm =
186nm =
µm
µm
mm
µm
nm
µm
Convert these measurements - answers
1.
2.
3.
4.
5.
6.
© OCR 2016
10mm =
3mm =
670 µm =
0.75mm =
24 µm =
186nm =
10 000µm
3 000µm
0.67mm
750µm
24 000nm
0.186µm
Quick quiz
© OCR 2016
What sort of microscope would you
use to…
• study the internal structure of a mitochondria?
© OCR 2016
What sort of microscope would you
use to…
• view sperm cells to see if they are moving?
© OCR 2016
What sort of microscope would you
use to…
• look at organisms, cells or tissues that are alive?
© OCR 2016
What sort of microscope would you
use to…
• view the surface of a bacterial cell?
© OCR 2016
What sort of microscope would you
use to…
• observe the double membrane around a
chloroplast?
© OCR 2016
What sort of microscope would you
use to…
• look at a cross-section
of a sample at high
resolution?
• What do you think this
is a picture of?
© OCR 2016
What sort of microscope would you
use to…
• look at a viral cell?
© OCR 2016
What sort of microscope would you
use to…
• look at the shape and surface of red blood cells
in detail?
© OCR 2016
What have we learnt using electron
microscopes?
• Cells contain organelles to carry out different
functions.
• The internal structure of organelles and how
they function.
• Structure of bacteria and viruses.
• Causes of medical conditions e.g. MS, HIV.
© OCR 2016
Objectives
Can you:
• explain how an electron microscope is different
to a light microscope
• define the terms magnification and resolution
• convert units of measurement used in
microscopy
• state with examples, when different microscopes
are used.
© OCR 2016
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