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The biological classification of species
To include the taxonomic hierarchy of kingdom, phylum, class, order, family, genus and species and domain
Taxonomic groups are the hierarchal groups of classification – domain, kingdom,
phylum (plural phyla), class, order, family, genus (plural genera) and species
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Hierarchal classification systems are often referred to as Linnaean classification
as Carl Linnaeus was the first to propose the system
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There are more groups down the hierarchy and the groups become
more similar and share more characteristics
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Viable offspring are offspring that survive but isn’t capable of producing
offspring e
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a mule (from horse and donkey)
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Scientists classify organisms to identify species, to predict characteristics and to find evolutionary links
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Classification systems don’t order observed organisms
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The binomial system of naming species and the advantage of such a system
The binomial nomenclature/system is the scientific naming of a species with a Latin name made of two parts – the first
indicating the genus (generic name) and the second the species (specific name)
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Two different species have the same specific name but different genera
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Saprophytic/Saprotrophic – organisms that acquire nutrients by absorption, mainly decaying material
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The current classification system used by scientists is
known as the ‘Three Domain System’ and was proposed by Carl Woes
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Domains, the new level classification (part of current classification system), group organisms using
differences in the cells’ ribosomal RNA, membrane lipid structure and their sensitivity to antibiotics
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The organisms in the different domains
contain a unique form of rRNA and different
ribosomes:
Eukarya – 80s ribosomes, RNA polymerase
contains 12 proteins
Archaea – 70s ribosomes, RNA polymerase
of different organisms contains between 8-10
proteins and is very similar to eukaryotic
ribosomes
Bacteria – 70s ribosomes, RNA polymerase
contains 5 proteins
In Woese’s system the Prokaryotae kingdom
becomes divided into two kingdoms –
Archaebacteria and Eubacteria
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Eubacteria are classified in their own kingdom
because their biochemistry is different to
Archaebacteria e
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contain peptidoglycan in
cell
walls,
Archaebacteria
don’t
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Eubacteria (true
bacteria) is found in all environments and is
the most familiar and common
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The relationship between classification and phylogeny (covered in outline only at AS level)
Phylogeny is the evolutionary relationships between organisms
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A phylogenetic/evolutionary tree is a diagram used to represent the
evolutionary relationships between organisms
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Phylogeny is related to classification because it is basis of
classification
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Phylogeny produces a continuous tree whereas classification
requires discrete taxonomical groups
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The evidence for the theory of evolution by natural selection
To include the contribution of Darwin and Wallace in formulating the theory of evolution by natural selection and
fossil, DNA (only genomic DNA at AS level) and molecular evidence
Charles Darwin sailed on HMS Beagle on its voyage around the world between 1831 and 1836
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He observed that many of the closely related species showed significant variation
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At the same time, Alfred Wallace was working on the theory of evolution and sent his ideas to Darwin
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In 1859, Darwin published his book, On the Origin of Species, in which he explained how organisms evolved from natural
selection
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Darwin’s book caused controversy at the time of its
publication as it conflicted with the religious view of God’s creation
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The diagram shows Darwin’s findings
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A is in a different taxonomic) group from the other 3
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The evolution of B, C and D diverged at the same point
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g
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g
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g
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g
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g
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Most viability occurs outside molecule’s functional regions
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 Cytochrome c (protein involved in respiration)
 Ribosomal RNA – very slow rate of substitution so used with fossil information to determine relationships between
ancestors
 Haemoglobin – similar structures indicate common ancestry
 DNA base sequence e
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chimpanzees and humans share at least 98% DNA – can be used to estimate last common
ancestor, chimpanzees are humans’ closest living relatives
 Order of amino acids in proteins can be used to estimate last common ancestor
The different types of variation
To include intraspecific and interspecific variation and the differences between continuous and discontinuous
variation, using examples of a range of characteristics found in plants, animals and microorganisms and both
genetic and environmental causes of variation
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Interspecific variation is the differences between organisms of different species
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g
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There is a
graduation in values from one extreme to the other, known as a continuum
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Discontinuous/Discrete variation the differences between individuals that cover discrete categories e
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gender, shape of
bacteria, blood group (human)
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Two factors cause variation:
 Genetic causes – Different alleles (variants) of a gene, mutations, chance and meiosis and sexual reproduction
causes genetic variation
 Environmental causes – weather, presence of scars, hair colour etc causes environmental variation
In most cases, variation is due to a combination of both
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A normal distribution has the same mean, mode and median,
has a bell-shape (symmetrical about the mean), 50% of the values are less than and 50%
greater than the mean, most values lie close to the mean value – the number of
individuals at the extremes are low
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The greater the standard

deviation, the greater the spread of the data
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When you calculate the standard deviation of data that display a normal distribution, generally:

The student’s t test is used to compare the means of data values of two populations
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Different sample sizes may be used
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Spearman’s rank correlation coefficient is used to consider the relationship
between two sets of data
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An adaption is a variation that increases the chances of survival
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Examples include body covering (scales) camouflage
(polar bear blends into ice), teeth (tigers have large canines), mimicry (prevents predators)
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Examples include survival behaviours (opossum playing dead), courtship (scorpions dance to attract
partner), seasonal behaviours (migration and hibernation)
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Examples include poison production (venomous
snakes), antibiotic production (produced by some bacteria to kill other bacteria) and water holding (storing water)
Many adaptions fall into more than one category
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g
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Convergent evolution is when organisms evolve similarities because the organisms adapt to similar environments or other
selection pressures
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An example is marsupial and
placental moles – both burrow through soft soil to find worms because they have a streamlined body shape and modified
forelimbs or digging, their fur allows smooth movement through the soil
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The mechanism by which natural selection can affect the characteristics of a population over time
To include an appreciation that genetic variation, selection pressure and reproductive success (or failure) results
in an increased proportion of the population possessing the advantageous characteristic(s)
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Selection pressures are factors that affect an organism’s chance of
survival or reproductive success
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This may be due to new alleles from mutations
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Successful organisms pass the allele encoding the
advantageous characteristics onto their offspring
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This process
is repeated for many generations until the proportion of individuals with the advantageous adaption increases
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How evolution in some species has implications for human populations
To include the evolution of pesticide resistance in insects and drug resistance in microorganisms
Sheep blowflies (Lucilia cuprina) lay their eggs in faecal matter around a sheep’s tail causing sores
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The pesticide diazinon was used to kill the blow flies, but some developed resistance to the insecticide and pass
on their resistant alleles to offspring
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Pre-adaption is
when an organism’s existing traits is advantageous for a new situation
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Antibiotic-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA) has develop resistance to antibiotics
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Non-resistant individuals died
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