Download domain bacteria

17-3 Modern Classification
Biologists are always revising taxonomies
THE TREE OF LIFE
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When looking under a microscope, biologists split all cells into 2 fundamental types, the basis for life into 2
groups:
o Eukaryotes -membraned-nucleus, organelles
 People, pangolins
o Prokaryotes – no membraned- nucleus, no organelles – smaller!
 Bacteria
Revising the Tree
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Systematists can’t assume that the organisms within the groups of cells are equally related
o Evolutionary relationships are based on homologous features
o Euks and proks do have homologous macromolecules – used to store&translate genetic info – when
these can be compared, biologists use the proteins&RNAs for phylogenetic analyses
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Carl Woese
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Proposed revision of system of classification for life on earth into 6 kingdoms
He compared rRNA sequences of diff organism – grouped to similarities (all organisms have ribosomes)
 The sequences changed little over time
 So rRNA is unique and useful for finding evolutionary relationships between earth’s organisms
THREE DOMAINS OF LIFE
After phylogenetic analyses of rRNa, scientists found new relationships between big groups – suggesting new tree of life
1. last universal common ancestor – data showed that all organisms got their rRNA genes from one ancient
form of life
2. all living things related to one of three lineages ; domains:
a. Bacteria, Archaea, Eukarya  most things we know like plants & animals
3. Archaea – more recently found, more surprising findings
-at first thought as bacteria, but it’s been found that it’s VERY diff from bacteria, and that this must have descended
from unique proks early in time
DOMAIN BACTERIA
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Single celled proks w/ cell wall
o Reproduce through cellular fission
All have: cell wall, plasma membrane, cytoplasm with
No complex organelles, at least 1 circular chromosome
No membrane bound DNA – no nucleus
Very small – 2 um vs. human cell is 6 um
Oldest found cell fossils!
DOMAIN ARCHAEA
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Proks with cell membranes and other unique properties
o Some are autotrophic – produce their own food by chemosynthesis
o Some produce waste products – like methane (flammable!)
Mainly in harsh environments
o Hot springs, deep sea thermal vents, salty lakes, intestines of animals
Because archaea is so unique, scientists think it may be the earliest organisms on earth
o Some think the cells closely interacted with bacteria- coevolved
o Led to theory of endosymbiosis - saying euks arose when ancient proks began living as one cell
DOMAIN EUKARYA
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Eukaryotic organisms –large cells, true nucleus , complex organelles
Includes plants, animals, fungi, etc
SIX KINGDOMS
1st kingdom aligns with domain Bacteria
2nd kingdom aligns with domain Archaea
Last 4 kingdoms align with domain Eukarya
Kingdom Eubacteria (UNDER BACTERIA DOMAIN)
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Means “true bacteria”, meant to distinguish from archaea (not bacteria!!)
Kingdom Archaebacteria (UNDER DOMAIN ARCHAEA)
- Means “ancient bacteria” – but now it’s considered so diff from bacteria scientists just say archaea
Kingdom Protista (EUKARYA)
- Called protists
- Basically euks that aren’t plants, animals or fungi – bad because it defines based on what it’s not
- Unicellular – hard to make generalizations, for protists are not similar to one another
o Biologists consider getting riid of taxon protista,
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Examples of unicellular protists: amoebas and paramecia
Multicellular: seaweed and mold
Kingdom Fungi
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Heterotrophic, eukaryotic; both uni and multicellular
o Unique: Absorb their nutrients, not ingest
Include mushrooms, rusts, smuts, mildews, molds
Kingdom Plantae
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Eukaryotic, multicellular plants
o Mostly autotrophic, using photosynthesis as energy
o Develop from embryos
Most live on land; moss, ferns, conifers, flowering plants
Kingdom Animalia
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Eukaryotic, multicellular, heterotrophic
Devlop from embryos
Most have symmetrical body organization & move in environment to find food
FUTURE TAXONOMIC SYSTEMS
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Just scientific models- subject to change!
Some Modern biologists – proposed new ways for 6-kingdom and 3-domain systems
o Kingdoms to replace protista***
Some want subkingdom or superorder to adapt Linnaean ways
Some just want cladistics over Linnaean categories