Year 1
A Level Biology
B4.2.2: Classification and Evolution
The biological classification of species
Biological classification: process by which living + extinct organisms are organised into
systematic groups based on similarities + differences between species
Carl Linnaeus (C18 botanist) proposed the first hierarchical classification system (‘Linnaean
classification’), in which large groups were continually subdivided down to the level of species
Taxonomy: study and practise of naming + classifying species + groups of species within the
hierarchical classification scheme
Hierarchical classification: arrangement of organisms into taxonomic groups of different ranks
Taxonomic rank: any level w/in the hierarchical classification system
Taxon: a group of organisms at any rank in the hierarchical classification scheme
- Most widely used until recently = hierarchy of 7 taxonomic groups
- Similar / related groups at one hierarchical level are combined into more inclusive
groups at the next, higher, level
- [__ move down hierarchy → more groups at each level but fewer organisms in each group
- share more of the same characteristics
Kingdom
Phylum (pl ‘phyla’)
Class
Order
Family
,Genus (pl ‘genera’)
Species
(King Phillip Cried Out For Good Soup)
1. K - largest group of organisms sharing common features
2. P - major subdivision of a kingdom
3. C - group of related orders, subdivision of a phylum
4. O - group of related families, subdivision of a class
5. F - group of closely related genera, subdivision of order
6. G - group of related species, subdivision of family
7. S - breed freely with one another
(can have a subspecies - a subgroup within a species that has different traits)
Eg. humans - Homo sapiens:
[D = Eukarya]
K = Animalia
P = Chordata
C = Mammalia
O = Primates
F = Hominidae
G = Homo
S = sapiens (have also had eg. homo erectus)
The higher the taxa, the more diversity is shown between individuals within a group (there is
more variation between organisms in the kingdom animalae than between organisms in the
class mammalia)
Species
- Smallest basic taxonomic unit used to define living organisms - each group cont only 1
type of organism
- Defined as group of organisms that can reproduce to produce fertile offspring
, - Eg. donkeys + horses are classified as belonging to different species because when bred
together, the offspring prod (hinny / mule) is infertile as their cells cont an odd no of
chromosomes (63) → meiosis / gamete production can’t take place correctly as all the
chromosomes must pair up
- Definition doesn’t take into account simple organisms that reproduce asexually!
● Current system may change again as new scientific discoveries are made eg. through
genome sequencing
Reasons why scientists classify organisms
➔ To create a world wide record of all living organisms - eg. All Species Foundation
➔ Identify species - easy to identify species a (new or old) organism belongs to
➔ Predict characteristics - likely a species in a group will share same specific characteristic
as other members
➔ Find evolutionary links - species in same group probably share characteristics because
they have evolved from a common ancestor
➔ Universal - scientists can share research worldwide → see links between different
organisms, even if they live on different continents
➔ [__ helps communication
➔ Convenience - make studying living organisms more manageable
★ Classification systems created to order observed organisms - NOT defined by nature
The binomial system of naming species and the advantage of such a system
- Linnaeus also founded the system of binomial nomenclature
- Convention of writing scientific names
- All species given a scientific name consisting of 2 parts
1. Genus - capitalised
2. species - lowercase
- If handwriting underline, if typing use italics
- No 2 species could have the same generic + specific name (could have same specific
name but their genus would be different)
A Level Biology
B4.2.2: Classification and Evolution
The biological classification of species
Biological classification: process by which living + extinct organisms are organised into
systematic groups based on similarities + differences between species
Carl Linnaeus (C18 botanist) proposed the first hierarchical classification system (‘Linnaean
classification’), in which large groups were continually subdivided down to the level of species
Taxonomy: study and practise of naming + classifying species + groups of species within the
hierarchical classification scheme
Hierarchical classification: arrangement of organisms into taxonomic groups of different ranks
Taxonomic rank: any level w/in the hierarchical classification system
Taxon: a group of organisms at any rank in the hierarchical classification scheme
- Most widely used until recently = hierarchy of 7 taxonomic groups
- Similar / related groups at one hierarchical level are combined into more inclusive
groups at the next, higher, level
- [__ move down hierarchy → more groups at each level but fewer organisms in each group
- share more of the same characteristics
Kingdom
Phylum (pl ‘phyla’)
Class
Order
Family
,Genus (pl ‘genera’)
Species
(King Phillip Cried Out For Good Soup)
1. K - largest group of organisms sharing common features
2. P - major subdivision of a kingdom
3. C - group of related orders, subdivision of a phylum
4. O - group of related families, subdivision of a class
5. F - group of closely related genera, subdivision of order
6. G - group of related species, subdivision of family
7. S - breed freely with one another
(can have a subspecies - a subgroup within a species that has different traits)
Eg. humans - Homo sapiens:
[D = Eukarya]
K = Animalia
P = Chordata
C = Mammalia
O = Primates
F = Hominidae
G = Homo
S = sapiens (have also had eg. homo erectus)
The higher the taxa, the more diversity is shown between individuals within a group (there is
more variation between organisms in the kingdom animalae than between organisms in the
class mammalia)
Species
- Smallest basic taxonomic unit used to define living organisms - each group cont only 1
type of organism
- Defined as group of organisms that can reproduce to produce fertile offspring
, - Eg. donkeys + horses are classified as belonging to different species because when bred
together, the offspring prod (hinny / mule) is infertile as their cells cont an odd no of
chromosomes (63) → meiosis / gamete production can’t take place correctly as all the
chromosomes must pair up
- Definition doesn’t take into account simple organisms that reproduce asexually!
● Current system may change again as new scientific discoveries are made eg. through
genome sequencing
Reasons why scientists classify organisms
➔ To create a world wide record of all living organisms - eg. All Species Foundation
➔ Identify species - easy to identify species a (new or old) organism belongs to
➔ Predict characteristics - likely a species in a group will share same specific characteristic
as other members
➔ Find evolutionary links - species in same group probably share characteristics because
they have evolved from a common ancestor
➔ Universal - scientists can share research worldwide → see links between different
organisms, even if they live on different continents
➔ [__ helps communication
➔ Convenience - make studying living organisms more manageable
★ Classification systems created to order observed organisms - NOT defined by nature
The binomial system of naming species and the advantage of such a system
- Linnaeus also founded the system of binomial nomenclature
- Convention of writing scientific names
- All species given a scientific name consisting of 2 parts
1. Genus - capitalised
2. species - lowercase
- If handwriting underline, if typing use italics
- No 2 species could have the same generic + specific name (could have same specific
name but their genus would be different)
