Biology Chapter 3

• Cells are measured in micrometers.
• Magnification is the ability to make an image appear larger.
• Resolution is the measure of clarity of the image created.
• Compound light microscope uses 2 lenses: ocular closer to the eye and objective closer to the specimen, and a light source.
• To find total magnification you must do objective x ocular power.
• Compound light microscopes can be used to view living and non-living specimens and must be mounted on a slide.
• Stereomicroscope or dissecting microscopes have a greater working distance between objective lens and specimen.
• The general characteristics of an electron microscope are: very large and expensive instruments, require special treatment of specimen and requires computers to create an image using electron deflection and absorption.
• There are 3 types of electron microscopes: transmission(TEM), Scanning(SEM) and scanning tunneling.
• Transmission(TEM): a beam of electrons directed at a thin slice of stained specimen placed in a vacuum(internal structure).
• Transmission electron microscopes can be used on non-living specimens only.
• Scanning(SEM): beam of electrons focused on a coated specimen placed in a vacuum which creates a detailed image of the surface.
• Scanning electron microscopes can be used on non-living specimens only.
• Scanning tunneling: uses a needle-like probe to focus a beam of electrons in a specific area of the specimen creating a 3-D image.
• Scanning tunneling electron microscopes can be used on living and non-living specimens.