Diversity

• Biological diversity


  Variety of life in all its forms, levels and combinations
• Levels of biological diversity

  • Ecosystem diversity
  • Species diversity
  • Genetic diversity
• Ecosystem diversity


  • Variety and frequency of different ecosystems such as marine coasts, grasslands and forests
• Components of an ecosystem

  • Microorganisms, plants and animals
  • They interact with each other, in for example, food webs, and with light, water, air, minerals and nutrients
• Ecosystem functioning


  • Provides 'services' upon which all life on earth depends, including maintaining atmospheric composition, nutrient recycling, climate regulation, pollination and soil formation
• Ecosystems are threatened by development projects, habitat loss and fragmentation from urbanization, trade, introduction of alien species, and global atmospheric changes such as climate change and stratospheric ozone depletion. Air, water and soil pollution are the major threats in the industrialized world
• Species


  A group of closely related organisms which are capable of interbreeding to produce fertile offspring
• Species


  • Represent a group of organisms which have evolved distinct inheritable features and which occupy a unique geographical area
  • Usually do not freely interbreed with other species for a number of reasons
  • Occasionally, two organisms which are genetically closely related can interbreed to produce infertile offspring
• Taxonomy


  The science of classifying living things
• Branches of taxonomy


  • Nomenclature - The naming of organisms
  • Systematics - the placing of organisms into groups

  
• Binomial nomenclature


  Each organism is given two latin names: a generic name which begins with a capital letter, and a specific name which begins with a lower case letter
• Taxonomic hierarchy


  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum
  • Kingdom

  
• Artificial classification systems are based on one or a few easily observable characteristics and are usually designed for practical purposes
• Natural classification systems try to use natural relationships between organisms, considering evidence which includes both internal and external features

  
• Phylogenetic classification


  Based on evolutionary relationships, where organisms belonging to the same group are believed to have a common ancestor
• Systematics


  The field of biology which studies the similarities and differences between species and seeks to determine phylogenies (patterns of relatedness)
• Phylogeny/phylogenetic tree


  A diagrammatic hypothesis about the history of the evolutionary relationships of a group of organisms

  
• Classification is important to enable us to sort out the huge complexity of organisms that exist and to understand the evolutionary relationships between them
• Classification systems are not perfect and have their limitations as they are human based and not a self-established natural condition, and are only as accurate as the current knowledge of each group of organisms allows
• Key


  A convenient tool enabling a biologist to identify an organism, consisting of a series of choices that lead the user to the correct name
• Dichotomous key


  • Consists of a set of organised couplets, therefore these keys always give two choices in each step
  • Couplets are presented in the form of pairs of numbered statements/leads
• A dichotomous key should end with a number which is one less than the number of organisms listed
• When creating a dichotomous key, one should choose contrasting and mutually exclusive statements, use constant characteristics rather than ones that disappear or vary, and use characteristics which can be directly observed
• Characteristics in a dichotomous key

  • Contrasting and mutually exclusive statements
  • Preceded by the name of the part to which they apply
  • Constant characteristics rather than ones that disappear or vary
  • Can be directly observed
  • Quantitative or qualitative measurements
  • Avoid vague terms like 'big' or 'small'
  • Generally available to the user
• There should be one less step than the number of organisms identified in any dichotomous key
• Viruses


  Infectious particles smaller than bacteria, lying in the area between living and non-living states

  
• Viruses


  • Range in size between 20nm and 300nm
  • Cannot be seen using the light microscope, can be seen using an electron microscope
  • Metabolically inert outside the host cell, only living when inside the host

  
• Virion


  A complete virus particle composed of a nucleic acid core surrounded by a protein coat

  
• Types of viral nucleic acid

  • DNA
  • RNA
• Capsid


  The protein coat surrounding the viral nucleic acid core
• Capsomeres


  The identical repeating subunits of protein that make up the capsid
• Envelope


  The lipid bilayer membrane surrounding the capsid of some animal viruses
• Envelope


  • Rich in proteins, lipids and glycoproteins
  • Derived from the host cell membrane but contains viral proteins
  • Allows the virus to attach to the host cell

  
• Types of viruses


  • Enveloped viruses
  • Non-enveloped/naked viruses

  
• Bacteriophage


  A virus that infects bacteria

  
• Bacteriophage T4


  • Consists of an icosahedral head with a DNA core, a neck and collar, a long tail sheath, and a complex base plate with tail fibres

  
• Lytic cycle of bacteriophage replication

  1. Attachment

  2. Penetration

  3. Replication

  4. Maturation/Assembly

  5. Lysis

  
• Lysogenic cycle


  Bacteriophage integrates its nucleic acid into the host genome as a prophage, replicating with the host cell

  
• Retrovirus


  A virus belonging to the Retroviridae family, containing an RNA genome and replicating via a DNA intermediate

  
• Retrovirus structure


  • Outer envelope derived from host plasma membrane
  • Envelope proteins
  • Capsid containing RNA and reverse transcriptase enzyme