11.1B Cell biology
11.4.2.1 measure cell sizes using a microscope
To calculate cell size using a microscope, the ocular micrometer must first be calibrated against the stage
micrometer. This calibration involves aligning the scales of both micrometers under a specific magnification.
For instance, if 50 divisions on the ocular micrometer align with 10 divisions on the stage micrometer (each
10 µm), then 50 ocular divisions equal 100 µm. The value of one ocular division can then be calculated by
dividing the stage micrometer value (100 µm) by the number of ocular divisions (50), resulting in 2 µm per
ocular division at that specific magnification.
This calibration process must be repeated for each different objective lens magnification used, as the value
of each ocular division changes with magnification. Once calibrated, the stage micrometer is removed, and
the specimen containing the cells to be measured is placed on the microscope stage. To measure a cell, its
length or width is aligned with the ocular micrometer scale.
The number of ocular divisions spanned by the cell is then multiplied by the calibrated value of one ocular
division for that magnification. For example, if a cell spans 15 ocular divisions at a magnification where one
ocular division equals 2 µm, the cell’s size is 30 µm.
o Magnification – how many times bigger the image of a specimen observed is in comparison to the
actual size of the specimen
o Resolution – ability to distinguish between two separate points. The higher the resolution of an image,
the greater the detail that can be seen
11.4.2.2 compare mechanisms for optical and electron microscopes and discuss advantages and
disadvantages of an electron microscope
Light (optical) Transmission electron Scanning electron
microscope microscope microscope
What is used to Beams of visible light Beams of electrons emitted in a vacuum
, make an image
Purpose Study internal structures Study the surface of a
of the cell specimen
Mechanism of work o The light source, o Electron beam is o Electron beam is
typically a halogen directed at a very focused on a
lamp, emits light thin slice of a specimen coated
that passes through specimen stained with a very thin
a condenser lens, with metal ions; layer of metal
which focuses the Some structures o The electrons that
light onto the become more bounce off the
specimen. heavily stained than specimen form an
o The light then others image on a
passes through the o These heavily fluorescent screen
objective lens, which stained parts absorb o The image shows 3D
further magnifies electrons; those that details of the
the image, and are lightly stained surface of the
finally through the allow electrons to specimen
eyepiece lens, which pass through
allows the viewer to o The electrons that
observe the pass through strike a
magnified image. fluorescent screen,
forming an image
which is viewed on a
computer screen
Specimen o Specimen needs to o Dry and dead o Dry and dead
preparation be thin and is specimen specimen
stained using a o Thin o Specimen coated
coloured dye for it o Stained with heavy with very thin layer
to be seen metals ions of metal
o Wet or dry
o Live or dead
Image 2D coloured image 2D black and white 3D black and white
image, that may be image than can be
colourised colourised
Magnification 1500x Up to 2,000,000x Up to 50,000x
Resolution 200nm 0.5nm 0.2nm
Advantages o Small and portable o Higher magnification and resolution
(can be sued almost o It is possible to investigate a greater depth of
anywhere) field
o Living and dead
material can be
observed
o Preparation of
material is relatively
quick and simple,
requiring only little
expertise
o Material is rarely
distorted by
11.4.2.1 measure cell sizes using a microscope
To calculate cell size using a microscope, the ocular micrometer must first be calibrated against the stage
micrometer. This calibration involves aligning the scales of both micrometers under a specific magnification.
For instance, if 50 divisions on the ocular micrometer align with 10 divisions on the stage micrometer (each
10 µm), then 50 ocular divisions equal 100 µm. The value of one ocular division can then be calculated by
dividing the stage micrometer value (100 µm) by the number of ocular divisions (50), resulting in 2 µm per
ocular division at that specific magnification.
This calibration process must be repeated for each different objective lens magnification used, as the value
of each ocular division changes with magnification. Once calibrated, the stage micrometer is removed, and
the specimen containing the cells to be measured is placed on the microscope stage. To measure a cell, its
length or width is aligned with the ocular micrometer scale.
The number of ocular divisions spanned by the cell is then multiplied by the calibrated value of one ocular
division for that magnification. For example, if a cell spans 15 ocular divisions at a magnification where one
ocular division equals 2 µm, the cell’s size is 30 µm.
o Magnification – how many times bigger the image of a specimen observed is in comparison to the
actual size of the specimen
o Resolution – ability to distinguish between two separate points. The higher the resolution of an image,
the greater the detail that can be seen
11.4.2.2 compare mechanisms for optical and electron microscopes and discuss advantages and
disadvantages of an electron microscope
Light (optical) Transmission electron Scanning electron
microscope microscope microscope
What is used to Beams of visible light Beams of electrons emitted in a vacuum
, make an image
Purpose Study internal structures Study the surface of a
of the cell specimen
Mechanism of work o The light source, o Electron beam is o Electron beam is
typically a halogen directed at a very focused on a
lamp, emits light thin slice of a specimen coated
that passes through specimen stained with a very thin
a condenser lens, with metal ions; layer of metal
which focuses the Some structures o The electrons that
light onto the become more bounce off the
specimen. heavily stained than specimen form an
o The light then others image on a
passes through the o These heavily fluorescent screen
objective lens, which stained parts absorb o The image shows 3D
further magnifies electrons; those that details of the
the image, and are lightly stained surface of the
finally through the allow electrons to specimen
eyepiece lens, which pass through
allows the viewer to o The electrons that
observe the pass through strike a
magnified image. fluorescent screen,
forming an image
which is viewed on a
computer screen
Specimen o Specimen needs to o Dry and dead o Dry and dead
preparation be thin and is specimen specimen
stained using a o Thin o Specimen coated
coloured dye for it o Stained with heavy with very thin layer
to be seen metals ions of metal
o Wet or dry
o Live or dead
Image 2D coloured image 2D black and white 3D black and white
image, that may be image than can be
colourised colourised
Magnification 1500x Up to 2,000,000x Up to 50,000x
Resolution 200nm 0.5nm 0.2nm
Advantages o Small and portable o Higher magnification and resolution
(can be sued almost o It is possible to investigate a greater depth of
anywhere) field
o Living and dead
material can be
observed
o Preparation of
material is relatively
quick and simple,
requiring only little
expertise
o Material is rarely
distorted by
