Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 26 The Tree of Life An Introduction to Biological Diversity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Changing Life on a Changing Earth Life is a continuum, e xtending from the earliest organisms to the great variety of species that exist today

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Earth formed about 4.6 Billion years ago Early Earth’s atmosphere contained Water vapor (H 2 O) Nitrogen (N 2 ) Carbon dioxide (CO 2 ) Hydrogen (H 2 ) Methane (CH 4 ) Ammonia (NH 3 ) Hydrogen sulfide (H 2 S) Carbon monoxide (CO) No O 2, why? Because it is too reactive Volcanic eruptions and asteroid bombardment persisted for the first 800 Million years Around 3800 MYA Earth cools enough to have liquid water condense.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Liquid water is VERY Important for life Why? Because interesting chemistry can happen in water Molecules are moving fast enough to collide and react, but not so fast that they break apart as soon as a new molecule forms As you can see the earliest evidence of life is observed 3500 MYA, only 300 million years after liquid water appears on earth.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is the earliest physical evidence if life? Stromatolites: 3.5 Billion year old fossilized bacterial mats 1. Scientists Lynn Margulis and Kenneth Nealson are shown collecting bacterial mats in a Baja California lagoon. 3. Some bacterial mats form rock like structures called stromatolites, Below: Shark Bay, Western Australia, 3000 year old stromatolites Figure 26.11a, b 2. A section through a mat shows layers of sediment that adhere to the sticky bacteria as the bacteria migrate upward. 4. This is a section of a fossilized stromatolite that is about 3.5 billion years old.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Handout: Introduction to Biological Molecules Building BlockPolymerPurpose or FunctionWhat elements is it made of? Amino AcidsProteinCatalyze reactions, maintain cell structure, cell movement, cell signaling, adhesion to surfaces Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur NucleotidesNucleic Acids (DNA and RNA) Information storage and transferCarbon, Hydrogen, Oxygen, Nitrogen, Phosphorus Fatty acids and glycerol LipidsForm the cell membrane, energy storage and cellular signaling Carbon, Hydrogen, Oxygen, and some phosphorus SugarsCarbohydrateStructure and support, energy storage, and cell signaling Carbon, Hydrogen, and Oxygen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What was happening in the 300 Million years between when liquid water forms and the first prokaryotic cells appear? Organic molecules needed for life formed through chemical reactions on early earth. What are the molecules needed for life? Building BlockPolymerPurpose or FunctionWhat elements is it made of? Amino AcidsProteinCatalyze reactions, maintain cell structure, cell movement, cell signaling, adhesion to surfaces Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur NucleotidesNucleic Acids (DNA and RNA) Information storage and transferCarbon, Hydrogen, Oxygen, Nitrogen, Phosphorus Fatty acids and glycerol LipidsForm the cell membrane, energy storage and cellular signaling Carbon, Hydrogen, Oxygen, and some phosphorus SugarsCarbohydrateStructure and support, energy storage, and cell signaling Carbon, Hydrogen, and Oxygen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How could early earth have formed these molecules? The necessary elements were present in the simple molecules in early earths atmosphere: –H 2 O, N 2, CO 2, H 2, CH 4, NH 3, H 2 S, CO, –PO 4 is a common salt found in rocks and soil. All that is needed is time and energy for chemical reactions to occur to make more complex molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 26.2 Electrode Condenser Cooled water containing organic molecules H2OH2O Sample for chemical analysis Cold water Water vapor CH 4 H2H2 NH 3 As material circulated through the apparatus, samples were collected for analysis. They identified a variety of organic molecules, including amino acids and complex, oily hydrocarbons. RESULTS Simulated conditions thought to have existed on early Earth. EXPERIMENT CONCLUSION Organic molecules, a first step in the origin of life, can form from conditions similar to early earth Miller and Urey’s Experimental Design

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Hypotheses for how biological molecules could have formed Under water near deep sea hydrothermal vents Ice: ice has been shown to catalyze formation of ribozymes, or “RNA Enzymes” Space on asteroids: Amino ccids have been found on meteorites. Figure 26.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Steps involving evolution of life – Simple inorganic molecules form biological macromolecules – Biological macromolecules form polymers. – Self Replicating RNAs were likely the first genetic material because they can function as enzymes and genetic information. – Self Replicating RNAs compete and the ones that function best in self replication increase in numbers – A primitive metabolism evolves – Self replicating RNA become packaged into membrane forming protocells. – DNA replaces RNA as the genetic material (it is more stable) RNA remains critical for translation of protein.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evidence for the RNA world hypothesis RNA molecules called ribozymes have been found to catalyze many different reactions, including – Self-splicing (cutting and pasting RNA together) – Making complementary copies of short stretches of their own sequence or other short pieces of RNA Figure 26.5 Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 33 55 55

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protocells 20  m (a)Simple reproduction. This lipo- some is “giving birth” to smaller liposomes (LM). (b)Simple metabolism. If enzymes—in this case, phosphorylase and amylase—are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products. Glucose-phosphate Phosphorylase Starch Amylase Maltose Phosphate Figure 26.4a, b

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings From simple Protocells to complex Eukaryotic Cells Early life was simple: genetic material, bound in a lipid membrane, simple metabolism, ribosomes to make proteins Bacterial life leaves its traces starting 3.5 Billion Years ago 2.7 BYA Photosynthetic Bacteria transform the atmosphere by producing oxygen 2.1 BYA Eukaryotic Cells Evolved through Endosymbiosis The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The evidence supporting an endosymbiotic origin of mitochondria and plastids includes – Similarities in inner membrane structures and functions – Both have their own circular DNA – Mitochondrial and Chloroplasts have ribosomes more similar to bacterial TEM of Chloroplast TEM of free-living Cyanobacteria

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1.2 BYA Multicellularity evolved several times in eukaryotes Bacteria had evolved mechanisms of cellular communication Eukarya had larger more complex cells and more complex genomes. and sexual reproduction. Eukarya were complex enough to evolve multicellularity Multicellularity= Specialization of cell structure and function!

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings So What does the Tree of Life Look Like?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The analogy of a clock – Can be used to place major events in the Earth’s history in the context of the geological record Figure Land plants Animals Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen Prokaryotes Origin of solar system and Earth Humans Ceno- zoic Meso- zoic Paleozoic Archaean Eon Billions of years ago Proterozoic Eon

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The absolute ages of fossils – Can be determined by radiometric dating Figure Accumulating “daughter” isotope Ratio of parent isotope to daughter isotope Remaining “parent” isotope Time (half-lives)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mass Extinctions The fossil record chronicles a number of occasions – When global environmental changes were so rapid and disruptive that a majority of species were swept away Figure 26.8 Cambrian Proterozoic eon Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene Number of families ( ) Number of taxonomic families Extinction rate Cretaceous mass extinction Permian mass extinction Millions of years ago Extinction rate ( ) PaleozoicMesozoic ,500 1,500 1, ,000 Ceno- zoic

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two major mass extinctions, the Permian and the Cretaceous – Have received the most attention The Permian extinction – Claimed about 96% of marine animal species and 8 out of 27 orders of insects – Is thought to have been caused by enormous volcanic eruptions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cretaceous extinction – Doomed many marine and terrestrial organisms, most notably the dinosaurs – Is thought to have been caused by the impact of a large meteor Figure 26.9 NORTH AMERICA Chicxulub crater Yucatán Peninsula

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Much remains to be learned about the causes of mass extinctions – But it is clear that they provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Earliest Multicellular Eukaryotes Molecular clocks – Date the common ancestor of multicellular eukaryotes to 1.5 billion years The oldest known fossils of eukaryotes – Are of relatively small algae that lived about 1.2 billion years ago

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Larger organisms do not appear in the fossil record – Until several hundred million years later Chinese paleontologists recently described 570-million-year-old fossils – That are probably animal embryos Figure 26.15a, b 150  m200  m (a) Two-cell stage (b) Later stage

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Colonial Connection The first multicellular organisms were colonies – Collections of autonomously replicating cells Figure  m

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The “Cambrian Explosion” Most of the major phyla of animals – Appear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian period

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phyla of two animal phyla, Cnidaria and Porifera – Are somewhat older, dating from the late Proterozoic Figure Early Paleozoic era (Cambrian period) Millions of years ago Late Proterozoic eon Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular evidence – Suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Continental Drift Earth’s continents are not fixed – They drift across our planet’s surface on great plates of crust that float on the hot underlying mantle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Often, these plates slide along the boundary of other plates – Pulling apart or pushing against each other Figure North American Plate Caribbean Plate Juan de Fuca Plate Cocos Plate Pacific Plate Nazca Plate South American Plate African Plate Scotia Plate Antarctic Plate Arabian Plate Eurasian Plate Philippine Plate Indian Plate Australian Plate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The formation of the supercontinent Pangaea during the late Paleozoic era – And its breakup during the Mesozoic era explain many biogeographic puzzles Figure India collided with Eurasia just 10 million years ago, forming the Himalayas, the tallest and youngest of Earth’s major mountain ranges. The continents continue to drift. By the end of the Mesozoic, Laurasia and Gondwana separated into the present-day continents. By the mid-Mesozoic, Pangaea split into northern (Laurasia) and southern (Gondwana) landmasses. Cenozoic North America Eurasia Africa South America India Madagascar Antarctica Australia Laurasia Mesozoic Gondwana At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. Pangaea Paleozoic Millions of years ago