classification and evolution Flashcards
classification of species
Taxonomy is the practice of biological classification
The biological classification system enables us to arrange species into groups based on their evolutionary origins and relationships
In this hierarchical system there is no overlap between groups and each group is called a taxon (plural taxa)
By grouping organisms into taxa it can make them easier to understand and remember
There are several different ranks or levels within the hierarchical classification system used in biology
Multiple smaller taxa can be put into one larger taxon
hierarchical classification
The hierarchical classification system of organisms in biology is used to organise and group similar organisms together so that they can be more easily understood
There are several taxonomic ranks that exist
All taxonomic ranks or ‘taxa’ make up a ‘taxonomic hierarchy’
taxonomic ranks
Species is the lowest taxonomic rank in the system
Similar species can be grouped in a genus (plural genera)
Similar genera can be grouped in a family
Similar families can be grouped into an order
Similar orders can be grouped into a class
Similar classes can be grouped into a phylum (plural phyla)
Similar phyla can be grouped into a kingdom
Similar kingdoms can be grouped into a domain
Domains are the highest taxonomic rank in the system
The first letters of all the different ranks below the domains can be remembered as:
Kings Play Chess On Fancy Gold Squares
Kittens Pounce Clumsily On Furry Green Spiders
Kingdom Phylum Class Order Family Genus Species
eukarya
Eukarya is the domain of all eukaryotes, distinguishable from Bacteria and Archaea which are both prokaryotic domains
Just like the other domains, Eukarya contains the taxonomic hierarchy of kingdom, phylum, class, order, family, genus and species
binomial system
A species is a group of organisms that are able to reproduce to produce fertile offspring
Binomials are the scientific names given to individuals species
Binomials consist of the organism’s genus and species name in modern Latin
For example, the binomial for humans is Homo sapiens and the binomial for dogs is Canis familiaris
Binomials are extremely useful for scientists as they allow for species to be universally identified - the binomial for a species is the same across the entire globe
naming species
Species are often given common names, but these common names are often differ between countries and do not always translate directly between different languages
In order to avoid confusion about what group of organisms scientists are talking about, all species are given a two-part scientific name using the binomial system
This naming convention was developed and established by the Swedish scientist Carl Linnaeus in the 18th Century
The binomial name is always italicized in writing (or underlined if it is not possible to italicise)
The genus name should have a capital letter but the species name should not.
classification of the three domain
Taxonomy is the practice of biological classification
It involves placing organisms into a series of categories or taxa
There are different ranks within the hierarchical classification system used in biology
The highest rank is the domain
There are three domains of life
Cell type has a major role in the classification of organisms into the three domains but do not confuse cell types and domains
The two cell types are prokaryotic cells and eukaryotic cells
Prokaryotic cells are easily distinguishable in that they lack a nucleus
Eukaryotic cells have compartmentalised structures, with at least their genetic material segregated from the rest of the cell in a nucleus
the three domains of life
Although it was well known that most forms of life could be divided into prokaryotes and eukaryotes, advances in the studies of molecular biology, biochemistry and cell structure in the latter part of the 20th century showed that the prokaryotes are not one uniform group
Based on molecular analyses of RNA genes in particular, and by looking at features such as ribosomal RNA (rRNA), aspects of protein synthesis and the structure of cell membranes and flagella, scientists realised that using cell type to classify organisms was insufficient and that prokaryotes could be divided into two separate groups (domains)
The three domains are:
Bacteria (prokaryotes)
Archaea (prokaryotes)
Eukarya (eukaryotes)
archaea
Organisms within this domain are sometimes referred to as the extremophile prokaryotes, as archaea were first discovered living in extreme environments (although not all archaea do)
Archael cells have no nucleus (and so are prokaryotic)
They were initially classified as bacteria until several unique properties were discovered that separated them from known bacteria, including:
Unique lipids being found in the membranes of their cells
No peptidoglycan in their cell walls
Ribosomal structure (particularly that of the small subunit) are more similar to the eukaryotic ribosome than that of the bacteria
Archaea have a similar size range as bacteria (and in many ways metabolism is similar between the two groups)
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
bacteria
These are organisms that have prokaryotic cells which contain no nucleus
They vary in size over a wide range: the smallest are bigger than the largest known-viruses and the largest are smaller than the smallest known single-celled eukaryotes
Bacterial cells divide by binary fission
Example: Staphylococcus pneumoniae is a species of bacteria that causes pneumonia
eukarya
Organisms that have eukaryotic cells with nuclei and membrane-bound organelles are placed in this domain
They vary massively in size from single-celled organisms that are only several micrometres across, to large multicellular organisms many-metres in size, such as blue whales
Eukaryotic cells divide by mitosis
Eukaryotes can reproduce sexually or asexually
Key differences between archaea & bacteria
Initially, all organisms within the Archaea domain were classified as Bacteria
Then several unique features possessed by Archaea were discovered that separated them from both Bacteria and Eukarya
The main differences between Archaea and Bacteria are seen in:
Membrane lipids
Ribosomal RNA
Cell wall composition
membrane lipids
The membrane lipids found in the cells of Archaea organisms are completely unique
They are not found in any bacterial or eukaryotic cells
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
Both 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 ribosomes than subunits in Bacterial ribosomes
The base sequences of ribosomal RNA in Archaea show more similarity to the rRNA of Eukarya than Bacteria
The primary structure Both 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 ribosomes than subunits in Bacterial ribosomes
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 of ribosome proteins in Archaea show more similarity to the ribosome proteins in Eukarya than Bacteria
composition of cell walls
Organisms from the Bacteria domain have cells that always possess cell walls with peptidoglycan
Organisms from the Archaea domain also have cells that always possess cell walls, however these do not contain peptidoglycan
