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Taxonomy : microorganisms and viruses. Chapter 9 . Taxonomy . Aristotle (384 – 322 BCE) described the dominance of humans over all living things as the scala natural or “ladder of nature” The science of classifying organisms

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  • Aristotle (384 – 322 BCE) described the dominance of humans over all living things as the scala natural or “ladder of nature”
  • The science of classifying organisms
    • Used to identify organisms and to represent the relationships among them
  • Usually uses a hierarchical system to classify where organisms are arranged in a series
taxonomic classification
Taxonomic Classification
  • Carl Linnaeus (1707 – 1778) developed our present system of classification, based on physical and structural features
  • Binomial Nomenclature is a method of naming organisms by using a two-part scientific Latin / Greek name:
    • The genus name
    • The species name
    • Ex: North American Black Bear – Ursusamericanus
  • The scientific name is always italicized
  • and only the genus name has the first
  • letter capitalized
binomial nomenclature
Binomial Nomenclature
  • The two name system provides an added advantage by indicating similarities in anatomy, embryology and evolutionary ancestry.
  • Example:
  • Tamiasciurus hudsonicus
  • Mustela erminea
  • Marmota monax
  • Mustela vison
levels of classification
Levels of Classification
  • There are currently 8 main taxa
    • Categories used to classify organisms
  • Did
  • King
  • Philip
  • Cry
  • Out
  • “For
  • Goodness
  • Sakes!?”
  • Some genes in Archaea are most closely related to human genes than to similar genes in bacteria
  • There are 6 Kingdom systems of Classification:
  • Eubacteria
    • Lacks nuclei, cell wall is often present and can reproduce asexually
  • Archaebacteria
    • Lives in extreme environments, cell wall is present
  • Protists
    • Live in aquatic / moist habitats, not cell wall
  • Fungi
    • Most are multicellular, cell wall present and mostly terrestrial
  • Plantae
    • All autotrophs, cell wall present, can reproduce sexually or asexually
  • Animalia
    • All heterotrophs, no cell wall, most reproduce sexually
  • Viruses do not it into the 6 kingdom classification system because they don’t display the most of the characteristics of living cells.
  • Outside of a cell, a virus is lifeless
  • Once the virus enters cell, it will replicate
  • Because of the unique characteristics of a virus, it occupies a position between living and non-living
viruses cont d
Viruses Cont’d.
  • Viruses are so small that they were not discovered until the invention of the electron microscope in 1934 and are measured in nanometers.
  • Ex: Human RBC = 7500 nm vs. influenza virus = 115 nm
viruses cont d1
Viruses Cont’d.
  • Two life cycles:
  • Lytic
  • At the end of this cycle, the host cell is destroyed upon release of the virus
    • Bacteriophages that cause lysis (destruction)is referred to as a virulent phage.
  • Lysogenic
  • A virus does not kill the host cell, but may coexist with the cell and be replicated through many generations
viruses cont d2
Viruses Cont’d.
  • Most bacteriophages have a fairly restricted host range
    • The limited number of host species, tissues or cells that a virus or parasite can infect
    • Ex: AIDS virus can only attach to a specific site on certain types of WBC (white blood cells)
  • In humans, many diseases are caused by viruses
  • The virus destruction of cells by the virus cause symptoms of disease
  • Some viruses can be prevented with vaccines by causing the body to produce antibodies
    • Example: polio or smallpox
viral replication
Viral Replication
  • Attachment
    • The virus recognizes the host through chemical signals and inserts its DNA / RNA into the cell
  • Synthesis
    • The viral DNA / RNA directs the host cell in replicating its viral components
  • Assembly
    • The viral nucleic acids, enzymes and proteins are assembled into new viruses
  • Release
    • The newly formed virus particles are released from the infected host cell
  • Come in many different shapes including:
    • Spherical - cocci [plural] or coccus [singular]
    • Rod-shaped – bacilli (plural) or bacillus (singular)
    • Spiral – spirilla (plural) or spirillum (singular)
eubacteria cont d
Eubacteria Cont’D.
  • Eubacteria can also be classified by respiration and modes of nutrition:
  • Obligate Aerobes: bacteria that require oxygen for respiration
  • Obligate Anaerobes: bacteria that conduct respiration processes in the absence of oxygen
  • Facultative Anaerobes: bacteria that prefer environments with oxygen but can live without it
beneficial bacteria
Beneficial Bacteria
  • Bacteria constitute most of the decomposers of plant and animal waste and are essential for recycling biological materials
  • Examples:
    • Nitrogen fixing bacteria
    • Intestinal bacteria
      • Food digestion and synthesizing vitamins in humans
    • Streptomyces
      • Source of antibiotics
harmful bacteria
Harmful Bacteria
  • Bacteria are probably best known for causing disease.
  • Bacteria can cause disease symptoms by the amount of cells burdening the host tissues, destroying host cells or by producing poisons.
  • Ex: Streptococcus Necrotizing Faciitis
  • Sexual reproduction is uncommon in bacteria, however it can occur in some intestinal bacteria
    • Conjugation can occur when a donor cell inserts a plasmid of DNA into the recipient cell through a pili
    • Ex: E. coli
  • Endospores are dormant cells that contain genetic material encapsulated by a thick wall
    • Develops when conditions are unfavourable
    • Can lay dormant for thousands of years!
    • When environmental conditions improve the wall will break down and the cell will become active again
  • Asexual Reproduction
    • Main method is binary fission
  • Extremophiles – meaning they inhabit environments that are extreme in comparison to a normal bacterial environment
  • Examples:
  • Very hot environments  geysers
  • Very cold environments  artic waters
  • High salt content environments  salt lakes
  • Extremely acidic or alkaline environments
  • First appeared about 1.5 billion years ago
  • Contain organelles such as ribosomes and mitochondria to carry out metabolic processes more efficiently
  • Mostly microscopic and unicellular, and found in fresh or salt water
  • Ex: Plankton
  • Made up of 3 distinct groups:
    • Plant-like protists (autotrophs)
    • Animal-like protists (heterotrophs)
    • Fungi-like protists (heterotrophs)
plant like protists
Plant-like Protists
  • The group is considered plant like because the organism contains chlorophyll, which is the pigment found in plants that traps sunlight energy for photosynthesis
  • Traditionally called algae, however now algae is grouped into two kingdoms:
    • Eubacteria
      • Ex: Cyanobacteria (blue – green algae)
    • Protista
      • Ex: Green, Brown and Red algae
plant like protists1
Plant-like Protists
  • The plant-like protists are broken down into 6 phyla:
  • Euglenophyta
    • Euglena, particularly abundant in stagnant water
  • Chrysophyta
    • Diatoms
  • Pyrrophyta
    • Dinoflagellates (posses two flagella)
  • Chlorophyta
    • Green algae
  • Phaeophyta
    • Brown algae
  • Rhodophyta
    • Red algae
animal like protists
Animal-like protists
  • Protozoa
  • All heterotrophs
  • Must move to consume food
    • Referred to as holozoic because they engulf their food
  • The major criteria used for classifying is locomotion:
    • Sarcodina
      • Move using pseudopods
    • Mastigophora (Zooflagellates)
      • Move by flagella
    • Ciliophora
      • Uses synchronized cilia to move
    • Sporozoa
      • Parasitic movement
animal like protists cont d
Animal-like protists cont’d
  • Large variation in size, can vary from 2 µm to 5 cm.
  • Can be free living or parasitic
  • Reproduction is usually asexual by binary fission, however they can produce sexually under certain conditions
  • Some engulf food, while others can absorb nutrients directly through the cell membrane.
fungi like protists
Fungi-like Protists
  • Referred to as slime moulds
  • Placed in the phylum Gymnomycota
    • Their name comes from the slimy trail left behind the mould as it moves
    • Moves very slowly, sometimes only a few millimeters a day
  • Inhabit cool, shady, moist places
  • May resemble protozoans during some life stages and become amoeba-like or have flagella
  • Does not always remain a single-celled organism