Week 1 Notes
The Unity and Diversity of Life
| I. How Diverse is Life?
A. Estimates of number of species ranges from 4-30 million, with some thinking even higher (100 million!). B. Nearly 1/2 are in tropics C. But only 1.5 million species have been categorized so far. II. Assessing diversity requires a system of classification A. Biologists originally divided life into 3, then 5 kingdoms 1. Bacteria 2. Protists 3. Fungi 4. Plants 5. Animals B. Today, based on genetic and morphological evidence we group organisms into higher levels of classification, known as Domains 1. Bacteria 2. Archaea 3. Eukaryotes C. What are lines of evidence for three domain scheme? 1. RNA a. near nucleotide 910 out of 1500: Bacteria AAACUCAAA Archaea AAACUUAAAG b. are nearly a dozen more sequences where Archaea sequences are more similar to eukaryotes than bacteria c. Here is a table of differences between bacteria and archaea: |
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| D. What distinguishes each domain
and kingdom?
1. Bacteria and Archaea a. single cell b. prokaryotic - no internal organelles (chloroplasts, mitochondria, nucleus, endoplasmic reticulum) c. most primitive types of organisms 2. Eukaryotes a. both unicellular and multicellular b. all cells have internal organelles 3. Protists a. a grab-bag kingdom of mostly uni-cellular organisms 4. Fungi a. have cell walls made of chitin b. have extracellular digestion c. multicellular d. genetically more similar to animals than plants, despite appearance 5. Plants a. have cellulose cell walls b. most perform photosynthesis - makes them autotrophs (make their own food) c. multi-cellular d. store food as starch 6. Animals a. no cell walls b. eat other organisms - are heterotrophs c. most prevalent are insects, and of these, beetles. J.B.S. Haldane, a famous evolutionary scientist, when asked about this, replied that he had "an inordinate fondness for beetles". E. What ties all life together? Where is the Unity? 1. all life is carbon based 2. all life uses DNA or RNA as genetic material 3. proteins used for all biological reactions - all enzymes are proteins 4. all life shares common biochemical pathways, i.e., glycolysis 5. all life uses ATP for energy 6. Eukaryotes appear to be derived from prokaryotes through process of endo-symbiosis (championed by Lynn Margulis, U. of Massachusetts) 7. Life seems to always have the capacity to evolve toward more complexity a. but sometimes evolution proceeds in the other direction and some organisms actually evolve to become simpler through time (retrograde evolution) F. History of Classification 1. Romans used to group organisms of similar appearance, called the groups genera (genus is singular term) 2. After the decline of the Roman empire, species were named using Latin 3. Polynomial system a. early names had up to 6-8 names for a species - very confusing b. were called polynomials 4. Binomial system a. binomial system first thought up by Caspar Bauhaus (1560-1624) b. Carl Linneaus - great Swedish botanist (1707-1778), championed naming species with just two names, binomial system c. each species known by its genus and species epithet i. White oak is Quercus alba ii. Humans are Homo sapiens iii. scientific names are usually italicized. The genus is capitalized, but not the species epithet 5. Classification systems are hierarchical - that is, organisms are grouped by their similarities. Groups of species with similarities are put into larger groups, and so on. 6. Here is the present hierarchical scheme from largest and most inclusive, down to species: Domain - largest grouping Kingdom - Bacteria, Archaea, Protists, Fungi, Plants, Animals Phylum - Arthropoda (lobsters, insects), Chordates (animals w/backbones) Class - mammals, dicot plants Order - primates, etc. Family - Hominids, or Beeches Genus - Humans, oaks Species - sapiens for humans, alba for white oak 7. Bacteria a. earliest fossils found are 3.8 BYO, suggesting that life evolved quickly as earth cooled b. bacteria and archeae around for 2.5 Billion years before higher forms evolved c. blue-green algae in this group (stromatolites in Australia similar to what may been around then 8. Eukaryotes a. oldest cells date back 1.8 BYA. b. much more complex than prokaryotes c. mitochondria and chloroplasts - similar size to bacteria (1-10 microns) i. these organelles have their own DNA, which is similar to prokaryote DNA 1. circular, naked, and no introns ii. organelles have double membrane - inner one more prokaryotic-like d. suggestive of endo-symbiosis events that resulted in creation of eukaryotes e. eventually, as oxygen built up in the atmosphere, the Krebs cycle and electron transport evolved which allowed organisms to be much more active f. Around 590 MYA, multicellular life exploded in diversity i. Cambrian explosion ii. Oxygen layer in atmosphere well developed by now, and harmful UV rays reduced iii. land could now be colonized iv. fungi and plants invaded first, around 420 MYA, followed by animals |