6. domains, kingdoms or both

CLASSIFICATION

• largest group was the ‘Kingdom’ and could be either plants or animals

• kingdoms then divided into smaller groups, with characteristics of organisms becoming more similar

• last group contained only 1 type of organism

• last 2 groups give the organism its binomial name

KINGDOMS

• Linnaeus first proposed that all living things be fitted into 2 main groups called the plant and animal kingdoms

• as tech advanced scientists began to see microscopic organisms including bacteria and protista

• structure of fungi was also seen to be very different from plants

• new system was developed based on morphology with 5 kingdoms

• In earlier system all prokaryotes are put into 1 kingdom, Monera

ARCHAEA

• but, genetic analysis has revealed that Archaea genes are more similar to plant and animal genes than other prokaryotes

• bc their genes contain ‘unused’ sections of DNA that are not used to make proteins but other prokaryotic genes don’t

• 1970’s- scientists discovered a new group of single celled organisms with no nucleus

• called these ‘Archaea’ and classified them as prokaryotic cells, grouping them with bacteria

3 DOMAINS

bc of this, a scientist called Woese proposed that all organisms should be divided into 3 domains

1. Eukarya (have cells with a nucleus and unused sections in genes)​

2. Archaea (have cells with no nucleus and unused sections in genes)​

3. Bacteria (have cells with no nucleus and no unused sections in genes)​

2 DOMAINS

• for yrs scientists only divided living organisms into 2 domains

• named them the eukaryotes (cells with a nucleus and complex cell structure) and prokaryotes (no nucleus)

• some scientists think that chloroplasts became part of ‘eukaryotic ancestor’ cells first while others think that mitochondria were the first endosymbionts (organism which lives inside the cells of another organism)

ENDOSYMBIONTS 1

ENDOSYMBIONTS 2

2 DOMAINS OR 3?

• scientists are using molecular phylogeny to investigate the domains further

• have looked at the internal structures of prokaryotes and eukaryotes and compared them to the biochemistry of the proteins involved in their ribosomes and enzymes

• as a result a new theory developed that there are 3 domains – two prokaryotic (Archaea and Bacteria) and eukaryota

DIFFERENCES OF DOMAINS

1. Archaea replicate by binary fission controlled by a cell cycle- seems homologous (similar) to the cell cycle in eukaryotes but is diff from replication in bacteria

2. membrane structure and membrane proteins of the archaea are unique– very diff from the similar ones in bacteria and eukaryotes- archaea have an ether link in their lipids making them branch and may give them extra strength in extreme environments

DOMAINS CHARACTERISTICS