Topic 2 bio

• Species is defined as a group of organisms that can reproduce to produce fertile offspring.
• Morphology is the overall form and shape of the organism.
• Anatomy is the detailed body structure as determined by dissectio.
• Organism shares features because they originally descend from a common ancestor.
• As technology advanced, microscope knowledge of biochemistry and eventually DNA sequencing allowed us to classify organisms using a more scientific approach.
• Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is). This means that the base sequences in a mammal's DNA are more closely related to all other mammals than to any other vertebrate groups.
• As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are.
• Organisms were first classified by a Swedish naturalist called Linnaeus in a way that allows the subdivision of living organisms into smaller and more specialised groups.
• The species in these groups have more and more features in common the more subdivided they get
• He named the organisms in Latin using the binomial system
• This binomial system of naming species has been an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus (always given A CAPITAL LETTER) and species (starting with a lower case letter).
• When typed binomial names are always in italics (which indicates they are Latin) e.g. Homo sapiens —————————
• In handwriting or printed text, the binomial name is underlined e.g. Homo sapiens.
• The sequence of classification is: Kingdom, Phylum, Class,Order, Family, Genus, Species.
• Keys are used to identify organisms based on a series of questions about their features.
• Dichotomous means 'branching into two' and it leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose. Each choice leads the user onto another two descriptions.
• Dichotomous keys are usually represented in one of two ways:

  • As a branching flowchart (diagrammatic representation)
  • As a series of paired statements laid out in a numbered sequence (descriptive representation)
• in order to successfully navigate a key, you need to pick a single organism to start with and follow the statements from the beginning until you find the name.
• You then pick another organism and start at the beginning of the key again, repeating until all organisms are named.
• To construct a dichotomous key:

  • STEP 1: List down the observable characteristics of the specimens, such as feathers or legs.
  • STEP 2: Organize the characteristics in order, starting with the most general ones before moving to the more specific ones.
  • STEP 3: Divide the specimens using statements or questions based on the most general characteristic.
  • STEP 4: Further divide the specimens based on the next contrasting characteristic, continuing until all specimens are identified.
  • STEP 5: Draw a dichotomous key diagram, either text-based or graphical.
  • STEP 6: Test the dichotomous key by going through the questions to identify a specimen
• Common Cell Structures

  The cells of all living organisms contain the following:

  • Cytoplasm
  • Cell membrane
  • DNA as genetic material (either found in the nucleus or free in the cytoplasm)
• When viewed under an electron microscope (at a much higher magnification), all cells also contain the following:

  • Ribosomes for protein synthesis
  • Enzymes for respiration (in many but not all types of cells; found in mitochondria)
• The first division of living things in the classification system is to put them into one of five kingdoms. They are:

  i. Animals

  il. Plants

  ili. Fungi

  iv. Protoctists

  v. Prokaryotes
• Main features of all animals:

  • they are multicellular

  > their cells contain a nucleus but no cell walls or chloroplasts

  • they feed on organic substances made by other living organisms
• Main features of all plants:

  • they are multicellular
  • their cells contain a nucleus, chloroplasts and cellulose cell walls

  > they all make their own food by photosynthesis
• Main features of all fungi (e.g. moulds, mushrooms, yeast)

  • usually multicellular, except yeast which is unicellular
  • cells have nuclei and cell walls not made from cellulose
  • do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition
  • cell wall mode of chitin
• Main features of all Protoctists (eg. Amoeba, Paramecium, Plasmodium)

  > Predominantly are unicellular

  • all have a nucleus, some may have cell walls and chloroplasts

  > some protoctists photosynthesise and some feed on organic substances made by other living things
• Main features of all Prokaryotes (bacteria, blue-green algae)

  • often unicellular
  • cells have cell walls (not made of cellulose)
  • and cytoplasm but no true nucleus or mitochondria
  • cell walls made of murein or peptidoglycan
• There are two main phyla within the animal kingdom: Vertebrates and invertebrates.
• All vertebrates have a backbone while invertebrates does not.
• Main features of Flowering plants
• Bacteria are classified in the kingdom Prokaryote
• Ciliates are classified in the kingdom Protoctist
• Species of ciliate found in sewage treatment works

  • Euplotes
  • Chilodonella
  • Paramecium
  • Didinium
  • Vorticella
• Protoctist has linear DNA
• Structural features distinguishing protoctist cells from prokaryote cells


  Protoctist has nucleus/nuclear membrane/nuclear envelope, circular DNA, cilia fused together
• Wheat plants are monocotyledons
• Rattus rattus refers to genus and species
• Viruses are not part of any classification system as they are not considered living organisms
• Main features of Viruses