Classification of living organisms

• Taxonomy


  Hierarchical system used to categorize organisms to the species level
• Taxonomic classification levels


  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Domain is the largest group and contains 6 Kingdoms
• Order is comprised of families sharing a set of similar nature or character
• Genus is a group including closely related species
• Species comprises related organisms that share common characteristics and can produce a fertile offspring
• The smallest level in taxonomic classification is Species
• The largest level in taxonomic classification is Domain
• According to more recent classifications, living organisms can be classified into 3 Domains and 6 Kingdoms
• The 3 Domains & 6 Kingdoms

  • Bacteria (Eubacteria)
  • Archaea (Archaebacteria)
  • Eukarya (Animalia, Plantae, Fungi, Protista)
• Bacteria


  • Cell wall made up of peptidoglycan
  • Membrane bound organelles are absent
• Archaea


  • Cell wall does not contain peptidoglycan
  • Can survive in harsh conditions (ex: Heat & acidity loving, Salt loving, & those that produce methane)
  • Membrane bound organelles are absent
• Eukarya


  • Membrane bound organelles are present
  • Large in size
• Animalia


  • Multicellular
  • Absent cell wall
  • Express heterotrophic nutrition
• Plantae


  • Multicellular
  • Cell wall made up of cellulose
  • Store carbohydrates in the form of starch
• Fungi


  • Cell wall made up of Chitin
• Protists


  • Do not photosynthesize
  • Do not possess highly specialized tissues or organs
• Viruses are not considered living thus, they are not part of this classification system, but have their own classification system
• The Human Immunodeficiency Virus is an example of a virus that causes AIDS (Acquired Immunodeficiency Syndrome)
• Archaea


  • Halophiles - Aerobic organisms that live in very salty environments
  • Thermoacidophiles - Organisms that live in hot and acidic conditions
  • Methanogens - Microorganisms that consume carbon dioxide & produce methane
• Gram Staining


  Method of staining used to classify bacterial species into Gram Positive and Gram Negative
• Gram Positive Bacteria


  • Appears dark purple when stained
  • Presence of a thick layer of peptidoglycan in the cell wall
• Gram Negative Bacteria


  • Appears pink when stained
  • Bacterial cell wall has a thin layer of peptidoglycan and high lipid content
• Bacterial Reproduction


  1. Conjugation - Genetic material transfer between bacteria

  2. Binary Fission - Asexual reproduction where parent cell splits into two identical daughter cells
• In optimal conditions, a single bacterial cell division could take 20 minutes
• Benefits of Bacteria


  • Normal Flora
  • Production of Food & Medicine
  • Nitrogen Fixation
• Diseases Caused by Bacteria

  • Respiratory Diseases
  • Skin Diseases
  • Digestive Tract
  • Nervous System
  • Sexually Transmitted Disease
• Viruses are classified based on the genetic material that they possess
• Virus


  Nonliving microorganism made up of genetic material contained within a protein coat
• Virus Structure


  • Protein Coat called capsid
  • Genetic Material - Can either be DNA or RNA
• Retroviruses


  • Their genetic material is made up of RNA instead of DNA
  • Use the enzyme reverse transcriptase to form DNA from RNA
• Viral Diseases


  • Sexually Transmitted Diseases
  • Respiratory Diseases
  • Childhood Diseases
  • Nervous System
  • Other
• Prions


  Proteins called proteinaceous infectious particle, that cause infection or disease
• Diseases caused by prions

  • Mad Cow Disease
  • Creutzfeldt-Jakob disease
• Types of Viruses


  • Helical
  • Polyhedral
  • Spherical
  • Complex