4.2.2 (c.(i)(ii)) the features used to classify organisms into the five kingdoms: Prokaryotae, Protoctista, Fungi, Plantae, Animalia . The evidence that has led to new classification systems, such as the three domains of life, which clarifies relationships

to include the use of similarities in observable features in original classification. To include the more recent use of similarities in biological molecules and other genetic evidence AND details of the three domains and a comparison of the kingdom and domain classification systems

classification of the 5 kingdoms

• most people thought there to be five kingdoms at the top of the classification hierarchy

• Prokaryote

• Protoctista

• Fungi

• Plantae

• Animalia

Prokaryota

• includes bacteria and blue-green bacteria

• Most are unicellular (some can be found as filaments of cells or groupings of similar cells known as colonies)

• cells have cell walls (not made of cellulose) and cytoplasm 

• no nucleus or mitochondria

• cells divide by binary fission

• Blue-green bacteria and some bacteria are autotrophic (they are photosynthetic)

• Many bacteria are heterotrophic (feeding by decomposing living or dead organic materials)

Protoctista

• are all eukaryotic

• can exist as single-celled organisms or a group of similar cells

• A group of Protoctista known as protozoa possess cells similar to animal cells

  • Their cells have no cell wall

• Another group of Protoctista known as algae possess cells similar to plant cells

  • Their cells have cellulose cell walls and chloroplasts

Fungi

• All fungi are eukaryotic cells

  • Possess non-cellulose cell walls (often made of polysaccharide chitin)

  • Don’t have cilia

• Fungi are heterotrophs:

  • use organic compounds made by other organisms as their source of energy + molecules for metabolism

  • They obtain this energy and carbon by digesting dead/decaying matter extracellularly or from being parasites on living organisms 

fungi 2

• Fungi reproduce using spores that disperse onto the ground nearby

• Fungi have a simple body form:

  • They can be unicellular

  • Some consist of long threads called hyphae that grow from the main fungus body and form a network of filaments called the mycelium

  • Larger fungi possess fruiting bodies that release large numbers of spores (this is how many fungi reproduce)

• The mould found on bread is actually a fungus: Rhizopus nigricans

Plantae

• Plants are multicellular eukaryotic organisms

• Plant cells:

  • have cell walls composed of cellulose

  • Possess large (and usually permanent) vacuoles that provide structural support

  • Are able to differentiate into specialized cells to form tissues and organs

  • Possess chloroplasts that enable photosynthesis (not all plant cells have chloroplasts)

  • Can sometimes have flagella

• They are autotrophs

  • meaning they can synthesize their organic compounds and molecules for energy use and build biomass from inorganic compounds

• Plants have complex body forms

  • They have branching systems above and below the ground

Animalia

• are also multicellular eukaryotic organisms

• cells able to differentiate into many different specialised cell types that can form tissues and organs

• Have small temporary vacuoles (for example, lysosomes)

• Have no cell walls

• Sometimes have cilia

• They are heterotrophs and have a wide range of feeding mechanisms

• Communication within their complex body forms takes place through a nervous system and chemical signalling

what are the three domians of life

• Bacteria (prokaryotes)

• Archaea (prokaryotes)

• Eukarya (eukaryotes)

Bacteria

• These are organisms that have prokaryotic cells which contain no nucleus

• Bacterial cells divide by binary fission

• Example: Staphylococcus pneumoniae is a species of bacteria that causes pneumonia

Archaea

• often referred to: extremophile prokaryotes as they were first found living in extreme environments (although not all archaea do)

• they have no nucleus

• Archaea have a similar size range as bacteria

• in many ways metabolism is similar between the two

• DNA transcription is more similar to that of eukaryotes

• Example: Halobacterium salinarum is a species of the archaea domain that can be found in environments with high salt concentrations like the Dead Sea

Eukarya

• Organisms that have eukaryotic cells with nuclei and membrane-bound organelles.

• divide by mitosis

• can reproduce sexually or asexually

why is classifying organisms using cell type, insufficient?

• Based on molecular analyses of RNA genes in particular, and by looking at features:

  • ribosomal RNA (rRNA),

  • aspects of protein synthesis

  • structure of cell membranes and flagella

• found that prokaryotes could be divided into two separate groups (domains)

membrane lipid differences

• The membrane lipids of Archaea consist of branched hydrocarbon chains bonded to glycerol by ether linkages

• The membrane lipids of Bacteria consist of unbranched hydrocarbon chains bonded to glycerol by ester linkages

Ribosomal RNA

• Archaea and Bacteria possess 70S ribosomes

• The 70S ribosomes in Archaea possess a smaller subunit that is more similar to the subunit found in Eukaryotic

• The base sequences of ribosomal RNA in Archaea show more similarity to the rRNA of Eukarya than Bacteria

• The primary structure of ribosome proteins in Archaea show more similarity to the ribosome proteins in Eukarya than Bacteria

cell wall differences

• bacteria domain have cells that always possess cell walls with peptidoglycan

• Archaea domain also have cells that always possess cell walls, however these do not contain peptidoglycan