Module 2 – Foundations in biology
2.1.1 Cell structure
(a) The use of microscopy to observe and investigate different types of cell
and cell structure in a range of eukaryotic organisms
LIGHT MICROSCOPE
Light microscopes use different lenses to reflect light and magnify an
image, viewed at the eyepiece. These microscopes have the lowest
resolution of about 0.2µm so are usually used to look at whole cells or
tissues. Most light microscopes have a maximum magnification of x1500,
but some can magnify up to x2000. Different stains highlight different
things for example haematoxylin stains the nuclei of animal cells blue,
allowing us to locate them more easily.
PROS CONS
Cheap Low resolution
Portable Low magnification
All images are produced in colour Most cells are colourless so require staining
Ability to view both living and non-living Not good at differentiating depth so difficult to
organisms and processes e.g. mitosis reconstruct models of cells/tissues
Easy to use – require little training
ELECTRON MICROSCOPES
Electron microscopes use fast moving electrons to form an image in a beam with a wavelength
of less than 0.05nm. The electrons are focussed using magnets onto a photographic plate. They
have a much greater resolution than light microscopes because the wavelength of electrons is
less than 1nm, smaller than visible light.
Scanning electron microscope
Scanning electron microscopes allow 3D images to be produced by
sending a beam of electrons, not through the specimen, but across
its surface. Reflected electrons are focussed onto a cathode ray
tube to form a black and white image, to which false colour can be
added using computer programs. The resolution is lower than that
of transmission electron microscopes, with a resolving power
between 1-3nm, but they have a magnification of up to x100 000,
allowing us to view the structure of tiny organisms such as
lymphocytes.
PROS CONS
Very high resolution Expensive to buy and maintain
Very high magnification Images are produced in B&W
Images can be artificially coloured using Researchers need training before they can use
computer programs them
Images can be viewed in 3D so surface of Require stable environments e.g. magnetic field
cells can be seen cancelling systems
All specimens must be in a vacuum – preparing
specimens is time consuming and requires skill
2.1.1 Cell structure
(a) The use of microscopy to observe and investigate different types of cell
and cell structure in a range of eukaryotic organisms
LIGHT MICROSCOPE
Light microscopes use different lenses to reflect light and magnify an
image, viewed at the eyepiece. These microscopes have the lowest
resolution of about 0.2µm so are usually used to look at whole cells or
tissues. Most light microscopes have a maximum magnification of x1500,
but some can magnify up to x2000. Different stains highlight different
things for example haematoxylin stains the nuclei of animal cells blue,
allowing us to locate them more easily.
PROS CONS
Cheap Low resolution
Portable Low magnification
All images are produced in colour Most cells are colourless so require staining
Ability to view both living and non-living Not good at differentiating depth so difficult to
organisms and processes e.g. mitosis reconstruct models of cells/tissues
Easy to use – require little training
ELECTRON MICROSCOPES
Electron microscopes use fast moving electrons to form an image in a beam with a wavelength
of less than 0.05nm. The electrons are focussed using magnets onto a photographic plate. They
have a much greater resolution than light microscopes because the wavelength of electrons is
less than 1nm, smaller than visible light.
Scanning electron microscope
Scanning electron microscopes allow 3D images to be produced by
sending a beam of electrons, not through the specimen, but across
its surface. Reflected electrons are focussed onto a cathode ray
tube to form a black and white image, to which false colour can be
added using computer programs. The resolution is lower than that
of transmission electron microscopes, with a resolving power
between 1-3nm, but they have a magnification of up to x100 000,
allowing us to view the structure of tiny organisms such as
lymphocytes.
PROS CONS
Very high resolution Expensive to buy and maintain
Very high magnification Images are produced in B&W
Images can be artificially coloured using Researchers need training before they can use
computer programs them
Images can be viewed in 3D so surface of Require stable environments e.g. magnetic field
cells can be seen cancelling systems
All specimens must be in a vacuum – preparing
specimens is time consuming and requires skill
