The Classification of Life

You Never Know!

The Classification of Life• How would you do it and why?• What can we learn from this exercise aboutthe evolutionary relationships amongorganisms on earth?

Classification Possibilities andPotential Strategies Based Upon:• Cell Structure and Complexity• Genetic Composition• Basic Metabolism Strategies and Mode ofLife• Size• Biotic History and Fossil Antiquity• Evolutionary Relationships

Darwin's Theory of NaturalSelection.• Fact #1 - Without constraints, populations will growexponentially, producing an ever more rapidly growingnumber of organisms.• Fact #2 - In spite of this prediction, the numbers ofindividuals in a population remains near equilibrium,fluctuating above and below some mean value. Why?• Fact #3 - Resources are limited.From these three facts, Malthus concluded that there was astruggle for existence.

Darwin’s Theory (Cont.):Darwin combined this with two addition facts:• Fact #4 - Sexually reproducing individuals are unique.There is individual variation across a population.• Fact #5 - Much (but not all) of the individual variation isheritable. This observation came from animal breeders.(Some of observed variation is environmental, some isgenetic.)These facts led Darwin to the conclude that some individualsare better equipped to survive and reproduce than others.This process came to be known as Natural Selection.• Through many generations of time, evolution is the result.(Darwin used "descent with modification.")

The Five Kingdom System?

A New Look at Life on Earth

Typical Prokaryote Organism ButAtypical in Ecologic Roles

Lithotrophs. Lithotrophy, a type of metabolism that requires inorganic compounds as sources of energy, isestablished in both the Archaea and the Bacteria. The methanogens utilize H2 as an energy source, and many extremethermophiles use H2S or elemental sulfur as a source ofenergy for growth. Lithotrophic Bacteria utilize inorganicsubstrates including H2, NH3, NO2, H2S, S, Fe++, and CO. Ecologically, the most important lithotrophic Bacteria are thenitrifying bacteria, Nitrosomonas and Nitrobacter that together convert NH3 to NO2, and NO2 to NO3, and the colorlesssulfur bacteria such as Thiobacillus that oxidizes H2S to S and S to SO4. Most lithotrophic bacteria are autotrophs, and, insome cases, they may play an important role in primary production of organic material in nature. Lithotrophic metabolismdoes not extend to eukaryotes (unless a nucleated cell harbors lithotrophic endosymbiotic bacteria), and these bacteria areimportant in the biogeochemical cycles of the elements.

Origins of Life?? Deep Sea VentCommunities

Why the Deep Sea??

Tectonic Picture

It’s a”Rockin Place”

Importance of Archaeans• Methanogens-facultative anaerobes reduceCO2 to CH4• Extreme Halophiles• Thermoacidophiles• More closely related to eukaryotes thanbacteria!• Life on other worlds? Mars? Europa?

Tube Worms--Life without aStomach!

Life on Other Planets?

Origins of Eukaryotes-TheEnvironmental Setting• Atmospheric Oxygen increases from nearzero to toxic levels about 2 billion years ago• Ozone Layer begins to form• Selection for organisms that could copewith oxygen

Mitochondria Do There Magic!

Significance of Eukaryote Evolution• Most significant single advance of organic evolution– Division of labor within the cell– Multicellular organisms evolved• Basic Organization of eukaryotic cells evolved once– Organelles striking similar to each other• Mitochondria• Plastids of autotrophs• Flagella– Biochemical similarities of all eukaryotes• Glucose metabolism• Krebs cycle• Protein synthesizing machinery

Possible Symbiotic Origins ofEukaryotes

The Five Kingdom System? IThink Not!!