4.3 Classification & Evolution

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4.3 Classification and Evolution
Biological Classification
Binomial system ­ a system that uses the genus name and the species name to avoid confusion
when naming organism
Classification ­ the process of placing living things into groups
Reasons for classification:
For convenience
To make the study of living things easier
For easier identification
To show the relationships between species
Modern Classification Hierarchy
Species ­ the basic unit of classification.
All members show variation but are
essentially the same
Genus ­ a group of closely related
Family ­ a group of closely related
Order ­ a subdivision of class using
additional information about organisms
such as meat eating (Carnivora) or
vegetation eating (Herbivora)
Class ­ a group of organisms with the
same general traits e.g. number of legs
Phylum ­ major subdivision of the
kingdom, contains all organisms with
the same body plan e.g. chordata (possessing backbone)
Kingdom ­ Five main kingdoms
Domain ­ highest taxonomic rank
As you descend the taxonomic ranks from Domain Species it becomes harder to distinguish and
separate closely related organisms from each other and to place them accurately.
Reasons for the binomial naming system:
The same organism may have a completely different common name in different parts of a
Different common names are used in different countries
Translation of languages and dialects may give different names
The same common name may be used for a different species in a different part of the
Using observable features for classification

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Species ­ a group of organisms that can freely interbreed to produce fertile offspring
This definition does not work for organisms that reproduce asexually and is very hard to apply to
organisms known only from fossil records and the like.
Phylogenetic definition of species ­ a group of individual organisms that are very similar in
appearance, anatomy, physiology, biochemistry and genetics
Early classification systems by Linnaeus and Aristotle were based solely on appearance and
features which limited the classification to observable features only.…read more

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Diffusion Saprophytic ­ Autotrophi Heterotrophi
of live on dead/ c ­ makes c ­ both
Diffusion of nutrients decomposing own food makes own
nutrients matter food and
eats other
Evidence used in Classification
Biological Molecules
Some biological molecules, such as those for DNA replication and respiration are essential
for life and therefore all living things have a variant that can be compared to show how
closely related they are.…read more

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Immunological Comparisons
Similar proteins will bind to the same antibodies. So, if antibodies to a human version
of a protein were added to isolated samples from other species, then any protein
similar to the human version will be recognised and bind to the antibody.
Artificial Classification ­ classification for convenience, e.g.…read more

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Divergent evolution is where another species has evolved from the original common ancestor and
the two species get progressively less similar.
Convergent evolution is where two species, who may share the same environment and therefore
the same factors that affect survival, evolve similar characteristics.…read more

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Variation ­ the presence of variety the differences between individuals
Intraspecific variation ­ variation between members of the same species
Interspecific variation ­ the differences between species
Continuous variation ­ variation where there are two extremes and a full range of values in
Discontinuous variation ­ variation where there are distinct categories and nothing in between
Causes of Variation
1.…read more

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Student's ttest ­ used to compare two means
Adaptation ­ a characteristic that enhances survival in the habitat
Anatomical adaptations ­ structural features
Behavioural adaptations ­ the ways that behaviour is modified for survival
Physiological adaptations ­ affect the way that processes work (also called biochemical)
Marram Grass (example)
Natural Selection
1. Mutation creates an alternative version of a gene (alleles)
2. This creates genetic variation between the individuals of a species (intraspecific variation)
3.…read more

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Therefore they pass on their advantageous characteristics (inheritance)
6. The next generation will have a higher proportion of individuals with the successful
characteristics. Over time, the group of organisms becomes well adapted to their
Pesticide Resistance in insects
An insecticide applies a very strong selection pressure. If the individual insect is susceptible then it
will die, but if it has resistance it will survive and reproduce, spreading the resistance through the
entire population.
e.g.…read more


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