viewing the microbial world

• metric units


  used to express the sizes of microbes
• meter (m)


  The basic unit of length in the metric system
• 39.4 


  one meter is equivalent to this in inches
• micrometers 


  metric unit in which the sizes of bacteria and protozoa are usually expressed
• micrometer 


  is one millionth of a meter
• 1 µm in diameter

  A typical spherical bacterium (coccus) is approximately
• 1 µm x wide 3 µm long


  A typical rod-shaped bacterium (bacillus) is approximately
• nanometers 


  The sizes of viruses are expressed in terms of
• nanometer 


  is equal to one billionth of a meter
• 10 to 300 nm


  Most of the viruses that cause human diseases range in size from
• Ebola virus


  a cause of viral hemorrhagic fever
• Ebola viruses 


  can be as long as 1,000 nm (1 µm)
• ocular micrometer


  When using a microscope, the sizes of microorganisms are measured using this
• microscope 


  is an optical instrument that is used to observe tiny objects, objects so small that they cannot be seen with the unaided human eye
• the resolving power or resolution


  Each optical instrument has a limit as to what can be seen using that instrument
• 0.2 mm


  The resolving power of the unaided human eye is approximately
• simple microscope


  a microscope that contains only one magnifying lens
• magnifying glass 


  could be considered a simple microscope as images appear 3 to 20 times larger than the object’s actual size when using this
• Leeuwenhoek’s simple microscopes 


  had a maximum magnifying power of about x300 (about 300 times)
• compound microscope


  a microscope that contains more than one magnifying lens
• compound light microscope

  Because visible light is the source of illumination, a compound microscope is also referred to as
• Compound light microscopes


  usually magnify objects about 1,000 times
• 0.2 µm 


  The resolving power of a compound light microscope is approximately
• wavelength of visible light


  It limits the size of objects that can be seen.
• The eyepiece or ocular lens and objective lens 


  the two magnifying lens systems in today's laboratory microscope
• ocular lens

  with x10 magnification
• scanning, low power, high power, and oil immersion 


  four commonly used objective lenses
• scanning 


  with 4x magnification
• low power


  with 10x magnification
• high power

  with x40 magnification
• oil immersion

  with x100 magnification
• Total magnification 


  is calculated by multiplying the magnifying power of the ocular lens by the magnifying power of the objective lens being used
• photomicrographs


  are photographs taken through the lens system of the compound light microscope
• brightfield microscope


  Because objects are observed against a bright background or “bright field,” the compound light microscope is sometimes referred to as a
• darkfield microscope

  If the condenser is replaced with what is known as a darkfield condenser, illuminated objects are seen against a dark background or “dark field”; the microscope is then called
• Phase-contrast microscopes and Fluorescence microscopes


  Other types of compound microscopes include
• Phase-contrast microscopes


  are used to observe unstained living microorganisms
• Fluorescence microscopes


  contain a built-in ultraviolet (UV) light source
• Electron microscopes 


  enable us to see extremely small microbes such as rabies and smallpox viruses
• electron beam


  the source of illumination