M2 Viewing the Microbial World

• Metric units

  Are used to express the sizes of microbes
• Meter

  It is the basic unit of length in the metric system
• 39.4 inches

  Equivalent of meter
• Micrometers

  The sizes of bacteria and protozoa are usually expressed in?
• What is the one millionth of a meter?

  Micrometer
• 1 micrometer in diameter

  What is the size of a typical spherical bacterium (coccus)?
• 1 micrometer wide x 3 micrometer long

  What is the size of a typical rod-shaped bacterium (bacillus)?
• Nanometers (nm)

  The size of viruses are expressed in terms of?
• It is equal to one billionth of a meter?

  Nanometer
• 10 to 300 nm

  Size of viruses that can cause human diseases
• Ebola virus

  Can be as long as 1,000 nm or 1 micrometer. It is a cause of a viral hemorrhagic fever.
• Ocular micrometer

  Sizes of microorganisms are measured using?
• Microscope

  It is an optical instrument that is used to observe tiny objects, objects than cannot be seen with unaided human eye.
• Resolving power or resolution

  The limit each optical instrument has as to what can be seen using that instrument.
• What is the resolving power of an unaided human eye? 0.2 mm
• Simple microscope

  It is one that contains only one magnifying lens
• 3 to 20 times larger

  Images appear to be in what size when using a magnifying glass?
• about x 300

  What is the maximum magnifying power of Leeuwenhoek's simple microscopes?
• Compound microscope

  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?
• about 1000 times

  Compound light microscopes usually magnify objects about?
• 0.2 micrometer

  The resolving power of a compound light mocroscope
• ~0.45 micrometer

  It is the wavelength of visible light that limits the size of objects that can be seen
• Eyepiece or ocular lens and Objective lens

  Two magnifying lens system of today’s laboratory microscope
• usually x10

  Eyepiece or ocular lens
• x4, x10, x40, x100

  Objective lens
• Total magnification

  Calculated by multiplying the magnifying power of the ocular lens x magnifying power of the objective lens
• Photomicrographs

  Photos taken through the lens system of the compound light microscope
• Brightfield microscope

  Objects are observed against a bright background or “bright field”, the compound light microscopes are sometimes referred to as?
• Darkfield microscope

  Condenser is replaced with what is known as a darkfield condenser, the microscope is then called a?
• Phase-contrast microscopes and Fluorescence microscopes

  Other types of compound microscopes
• Phase contrast microscopes

  Are used to observe unstained living microorganisms
• Fluorescence microscopes

  Contain a built-in Ultraviolet (UV) light source
• Electron microscopes

  It enables us to see extremely small microbes such as rabies and smallpox viruses
• No

  Can living organisms be observed using an electron microscope?
• Electron beam

  It is used as the source of illumination
• Magnets

  Are used to focus the beam
• True

  Electron microscopes have a much higher resolving power than compound light microscopes
• Transmission and Scanning

  Two tyoes of electron microscopes
• Transmission Electron Microscope

  This microscopes uses an electron gun to fire a beam of electrons through an extremely thin specimen