Viewing the Microbial World

• Metric units are used to express the sizes of microbes.
• The basic unit of length in the metric system is the meter (m); it is equivalent to 39.4 inches.
• The sizes of bacteria and protozoa are usually expressed in terms of micrometers (µm). A micrometer is one-millionth of a meter
• A typical spherical bacterium (coccus) is approximately 1 µm in diameter.
• A typical rod-shaped bacterium (bacillus) is approximately 1 µm wide x 3 µm long.
• The sizes of viruses are expressed in terms of nanometers (nm). A nanometer is equal to one billionth of a meter
• Most of the viruses that cause human diseases range in size from 10 to 300 nm
• One exception is Ebola virus, a cause of viral hemorrhagic fever. Ebola viruses can be as long as 1,000 nm (1 µm).
• When using a microscope, the sizes of microorganisms are measured using an ocular micrometer
• Answer

  A) 0.001 or 1 x 10^-3

  B) 1,000,000,000 or 1 x 10^9

  C) 10,000,000,000 or 1x10^10

  D) 0.01 or 1x10^-2

  
• Microscope - it is the ultimate tool in studying microbiology
• The human eye, a telescope, a pair of binoculars, a magnifying glass, and a microscope are various types of optical instruments.
• A 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.
• three main properties of the microscope:

  1. Magnifying Power
  2. Resolving Power
  3. Contrast
• Magnifying power - how much larger a given lens can make an image appear
• Resolving power - how far apart two adjacent objects must be before a given lens shows them as discrete entities.
• The resolving power of the unaided human eye is approximately 0.2 mm.
• Contrast - ability needed to distinguish detail between adjacent objects.
• Robert Hooke - he first used a microscope in 1667
• Antonie van Leeuwenhoek - he used as single-lens microscope and observed "animacules" in 1675
• Zaccharias Jansen - he invented the first compound microscope in 1600's
• Joseph Jackson Lister - he developed a significantly better microscope in 1830
• A simple microscope is one that contains only one magnifying lens.
• A magnifying glass could be considered a simple microscope; when using a magnifying glass, images appear 3 to 20 times larger than the object’s actual size.
• Leeuwenhoek’s simple microscopes had a maximum magnifying power of about x300 (about 300 times).
• A compound microscope contains more than one magnifying lens.
• Because visible light is the source of illumination, a compound microscope is also referred to as a compound light microscope.
• The resolving power of a compound light microscope is approximately 0.2 µm (about 1,000 times better than the resolving power of the unaided human eye).
• It is the wavelength of visible light (~0.45 µm) that limits the size of objects that can be seen.
• Objects cannot be seen if they are smaller than half of the wavelength of visible light.
• Today’s laboratory microscope contains two magnifying lens systems:

  1. eyepiece or ocular lens
  2. objective lens
• ocular lens - it is usually x10
• objective lens - x4, x10, x40, and x100 are the four most commonly used
• The parts of a microscope can be categorized into:

  1. Mechanical
  2. Magnifying
  3. Illuminating
• Mechanical part - it is for support and adjustment
• Magnifying part - it is for enlargement of the observed specimen
• Illuminating part - It is for light provision
• Mechanical parts are:

  1. Base
  2. Arm
  3. Stage
  4. Inclination Joint
  5. Body tube
  6. Draw tube
  7. Revolving nosepiece
  8. Dust shield
  9. Coarse adjustment knob
  10. fine adjustment knob
  11. slide movement knobs
• Base - holds various parts of the microscope including the light source.
• Arm - connects the eyepiece and the objective lens