The tree of life

1
The tree of life

• Chapter 26

2
Fundamental properties of life

• Cellular organization
• Sensitivity
• Growth
• Development
• Reproduction
• Regulation
• Homeostasis
• Heredity

3
Classification of organisms

• More than 2000 years ago, Aristotle divided
  living things into animals and plants
• Later, basic units became known as genera
• Singular genus
• Latin
• Felis (cats) and Equus (horses)
• In the 1750s, Carolus Linnaeus institued the use
  of two-part names, or binomials
• Homo sapiens
• Common names make poor names

4
Classification of organisms

• Taxonomy is the science of classifying living
• A classification level is called a taxon
  (pluraltaxa)
• Taxa are based on shared characteristics
• Linnaean hierarchy
• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

5
Hierarchical system of classification
6
Limitations of the hierarchy

• Many hierarchies are being re-examined based on
  the results of molecular analysis
• Linnaean taxonomy does not take into account
  evolutionary relationships
• Linnaean ranks are not equivalent
• Legume family has approximately 16,000 species
• Cat family has only 36 species
• The phylogenetic and systematic revolution is
  underway

7
Grouping organisms

• Carl Woese proposed a six-kingdom system
• Now biologists are increasingly adopting a
  three-domain phylogeny based on rRNA studies
• Domain Archaea
• Domain Bacteria
• Domain Eukarya
• Each of these domains forms a clade
• Archaea and Eukarya are more closely related to
  each other than to Eubacteria

8
During evolution, microbes swapped genetic
information via horizontal gene transfer (HGT)
9
Eubacteria

• Most abundant organisms on Earth
• Extract nitrogen from the air, and recycle carbon
  and sulfur
• Perform much of the worlds photosynthesis
• Responsible for many forms of disease
• Highly diverse
• Most taxonomists recognize 12-15 different groups

10
Archaea

• Prokaryotes that are more closely related to
  eukaryotes
• Characteristics
• Cell walls lack peptiodoglycan
• Membrane lipids are branched
• Distinct rRNA sequences
• Divided into 3 main groups
• Methanogens
• Use H2 to reduce CO2 to CH4
• Strict anaerobes that live in swamps
• Extremophiles
• Thermophiles high temperatures
• Halophiles high salt
• Acidophiles low pH
• Nonextreme archaea
• Grow in same environments as bacteria
• Nanoarchaeum equitans Smallest cellular genome

11
(No Transcript)
12
Eukarya

• Eukaryotes have a complex cell organization
• Extensive endomembrane system divides the cell
  into functional compartments
• Mitochondria and chloroplasts most likely gained
  entry by endosymbiosis
• Mitochondria were derived from purple nonsulfur
  bacteria
• Chloroplasts from cyanobacteria

13
Four eukaryotic kingdoms

• Protista
• Unicellular with few multicellular organisms
• Not monophyletic
• Plantae
• Animalia Largely multicellular
• Fungi

14
Key eukaryotic characteristics

• Compartmentalization
• Allows for increased subcellular specialization
• Multicelluarity
• Allows for differentiation of cells into tissues
• Sexual reproduction
• Allows for greater genetic diversity

15
(No Transcript)