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CONTENTS
4.3.1 Classification of Species 4.3.2 Binomial System 4.3.3 Classification of the Three Domains 4.3.4 Classification of the Five Kingdoms 4.3.5 Classification & Phylogeny 4.3.6 Evidence of Evolution 4.3.7 Types of Variation 4.3.8 Standard Deviation 4.3.9 Variation: t-test Method 4.3.10 Variation: t-test Worked Example 4.3.11 Spearman's Rank Correlation 4.3.12 Adaptation 4.3.13 Natural Selection 4.3.14 Evolution of Resistance 4.3.15 Consequences of Resistance
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OCR A Level Biology Revision Notes
4.3 Classification & Evolution
YOUR NOTES
4.3.1 CLASSIFICATION OF SPECIES
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
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4.3 Classification & Evolution
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’ 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 There are a few different rhymes that exist to help you remember the different ranks in the taxonomic classification system. A couple of examples are given below but you could always make up your own! The first letters of all the different ranks below the domains can be remembered as: K ings P lay C hess O n F ancy G old S quares K ittens P ounce C lumsily O n F urry G reen S piders K ingdom P hylum C lass O rder F amily G enus S pecies The hierarchical classification system – The higher ranks contain more organisms with
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4.3 Classification & Evolution
A wolf is an example of an organism in the Eukarya domain It can be classified further into its kingdom, phylum, class, order, genus and species A wolf belongs to the following taxonomic groups: Domain : Eukarya Kingdom : Animalia Phylum : Chordata Class : Mammalia Order : Carnivora Family : Canidae Genus : Canis Species Canis lupus The classification of a Wolf
Exam Tip
The name of a species always consists of two words: the genus and species. This means when provided with the Latin name of a species you
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4.3 Classification & Evolution
The Hibiscus rosa-sinensis (a colourful flowering plant) is another example of an organism in the eukarya domain It belongs to the following taxonomic groups: Domain : Eukarya Kingdom : Plantae Phylum : Angiospermae Class : Dicotyledonae Order : Malvales Family : Malvaceae Genus : Hibiscus Species : Hibiscus rosa-sinensis A Classification Table
Exam Tip
The binomial for a species is always typed in italics or underlined when handwritten. The genus name should have a capital letter but the sp
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4.3 Classification & Evolution
4.3.2 BINOMIAL SYSTEM
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) For example: The most commonly known yeast is Saccharomyces cerevisiae It is common to abbreviate the genus name (e.g. S. cerevisiae ) Saccharomyces paradoxus is another species of that is a member of the same genus as cerevisiae
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4.3 Classification & Evolution
4.3.3 CLASSIFICATION OF THE THREE DOMAINS
Classification of the Three Domains
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)
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4.3 Classification & Evolution
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 Example: Canis lupus , also known as wolves
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 of ribosome proteins in Archaea show more similarity to the ribosome proteins in Eukarya than Bacteria
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4.3 Classification & Evolution
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 Characteristics & features of the three domains table
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4.3 Classification & Evolution
A typical bacterial cell The other kingdoms can all be classified within the domain Eukarya , which can be divided into the following four kingdoms: Protoctis ta Fungi Plantae Animalia Organisms from each of these four kingdoms have distinct characteristics and features, but share similarities in that they have cells with membrane-bound nuclei separating genetic material from the cytoplasm, and compartmentalisation within their cells as a result of the presence of other organelles
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4.3 Classification & Evolution
The four kingdoms within the Eukarya domain: protoctista, fungi, plantae and animalia
Kingdom Protoctista
All Protoctista are eukaryotic, and this broad group of cellular life encompasses all eukaryotic cells that do not belong to the other three eukaryotic kingdoms Members of this kingdom show great diversity in all aspects of life including structure, life cycle, feeding and trophic levels and well as modes of locomotion Protoctists can exist as single-celled organisms or as 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
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4.3 Classification & Evolution
A typical fungal cell
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4.3 Classification & Evolution
The structure of a fungus with its hyphae, mycelium and fruiting bodies
Kingdom Plantae
Plants are multicellular eukaryotic organisms Plant cells: All 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 This means they can synthesize their organic compounds and molecules for energy use and building biomass from inorganic compounds Plants have complex body forms They have branching systems above and below the ground
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4.3 Classification & Evolution
A typical animal cell
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4.3 Classification & Evolution
Five Kingdoms Comparison Table
