AQA AS Biology Unit 2: Classification

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  • Created on: 22-08-13 17:08
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Classification The organisation of living organisms into groups
based on a number of accepted principles
A species is the basic unit of classification.
Members of a single species have certain things in common:
They are similar to one another but They have very similar genes and therefore
different from members of other species closely resemble one another physically and
They have similar patterns of development
and similar immunological features and they
occupy the same ecological niche
They are capable of breeding to produce, They are therefore able successfully to
living, fertile offspring produce more offspring
This means that, when a species reproduces
sexually, any of the genes of its individuals
can, in theory be combined with any other,
i.e. they belong to the same gene pool
Ecological niche Describes how an organism fits into its environment
It describes what a species is like, where it occurs,
how it behaves, its interactions with other species and
how it responds to its environment
Gene pool The total number of alleles in a particular population
at a specific time

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Naming a Species ­ the Binomial System
Organisms are identified by two names and hence the system is called the binomial system.…read more

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The Principals of Classification
The grouping of organisms is known as classification, while the theory and practice of
biological classification is called taxonomy.
There are two main forms of biological classification:
Artificial Classification Divides organisms according to differences that are
useful at the time
Such features may include colour, size, number of legs,
leaf shape etc.…read more

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Taxonomy is the science of classification.
It involves naming organisms and organising them into groups based on their similarities
and differences.
Each group within a biological classification is called a taxon.
Taxonomy is the study of these groups and their positions in a hierarchical order, where
they are known as taxonomic ranks.
These are based upon their evolutionary line of descent of the group members.
The largest group is a kingdom and each organism is placed into one of these.…read more

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The evolutionary relationship between organisms is known as phylogeny.
The term is derived from the word phylum, which, in classification, is a group of related or
similar organisms.
The phylogeny of an organism reflects the evolutionary branch that led up to it.
The phylogenetic relationships of different species are usually represented by a tree-like
diagram called a phylogenetic tree.…read more

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Difficulties of Defining Species
A species may be defined in terms of observable similarities and the ability to produce
fertile offspring.
There are, however, certain difficulties with this definition.…read more


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