Chapter 10: Classification and evolution
The biological classification of species
The taxonomical hierarchy is used to classify species: it defines all species into increasingly specific groups in this order:
Domain, kingdom, phylum, class, order, family, genus, species
- You can remember this with the pneumonic “dumb king Philip could only find gold spades”
The binomial system of naming species
Every species is given a unique name using “the binomial system”. This standardised system allows all scientists to
communicate in the same language, identification of species, prediction of characteristics.
Each name is two words where the first is the genus (also called the generic name) and the second is the species (as the
last two and the most specific groups in the taxonomical hierarchy).
The first letter of the genus is capitalised, the species is all lowercase
Both words are italicised (underlined if handwritten)
Examples are Homo sapiens and Caenorhabditis elegans
The features use to classify organisms into 5 kingdoms
Kingdom Defining features
Prokaryotes Unicellular, no nucleus, no membrane bound organelles
Protista Have a membrane bound nucleus and membrane bound organelles. Some are unicellular, some are
multicellular some have chloroplasts. They move in a variety of ways and have a variety of nutrient
acquirement methods. A very miscellaneous kingdom.
Fungi Have a membrane bound nucleus and membrane bound organelles, no chlorophyll, food is stored as
glycogen, no locomotive mechanisms.
Plants Have a membrane bound nucleus and membrane bound organelles (including chloroplasts), cell wall is
mainly composed of cellulose, all have chlorophyll, nutrients are acquired by photosynthesis, food is
stored as starch.
Animals Have a membrane bound nucleus and membrane bound organelles, no chloroplasts, a variety of
locomotive mechanisms, multicellular
Evidence for the “new” classification system (it’s not that new!)
There used to be considered that there were 2 domains of life: prokaryotes and eukaryotes. There is now considered to
be 3: Bacteria, Archaea and Eukarya (where the first two used to be considered under the one domain of prokaryotes).
This separation is based on differences in biological molecules such as DNA, proteins (cytochrome C) and genetic
evidence.
From this it follows that there must also be another kingdom, there are 6 kingdoms of life (where prokaryotes are
replaced with Archaebacteria and Eubacteria) but you will only need to consider the 5 kingdoms.
The relationship between classification and phylogeny
Phylogeny is the evolutionary relationship between organisms where closer branches are more closely related. This
continuous tree of classification can be misleading though as organisms that are close on a phylogenetic tree may still be
relatively distantly related.
Evidence for the theory of evolution by natural selection
Charles Darwin developed the theory of evolution by natural selection with Alfred Wallace, who had similar ideas at the
same time. They shared ideas and peer reviewed each other’s work and jointly published work.
Evidence for evolution includes:
- The fossil record allows the relationship between extinct and living organisms to be investigated
