BIO_SC 1010 1st Edition Lecture 18 Outline of Last Lecture I. Evolutionary Relationships may be represented by branching treesII. Clades van be thought of representing a branch on the tree of lifeIII. New SpeciesIV. HomologyV. DNA sequencesVI. Descent with ModificationVII. Fossil RecordVIII. Radiometric DatingOutline of Current Lecture II. Early LifeIII. When and how did Life Begin?IV. ProkaryotesV. Eukaryotes Current LectureEarly Life• Scientists estimate that the age of the solar system more generally is 4.54 billion years• Life on Earth likely appeared about 3.9 billion years ago-early Earth was not very hospitable to life-although we will never know for certain how life on Earth originated, scientists can hypothesizeabout what may have occurred • Biologists hypothesize that life originated in a series of stages-one hypothesis is that the unique conditions of primordial Earth fostered biogenesis, the formation of new living organismsWhen and how did Life Begin?• Miller and Urey (1953) hypothesized that they could synthesize organic molecules by replicating the chemical environment of the early earth These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Scientists hypothesize that, over millions of years, cells capable of reproducing formed • Organic monomers can form under conditions that simulate early Earth-nucleotides, amino acids• Early Earth’ extreme conditions may have bonded monomers into organic polymersProkaryotes• Prokaryotes were the first groups of life to evolve on Earth• prokaryotes have relatively small, simple cells• for the first billion years, they were the only life on planet Earth• today, prokaryotes are found everywhere there is life, including many places where no other life can survive • Two of the domains of life consist of prokaryotes: Bacteria and Archaea-domain Bacteria: unicellular, found everywhere, some causes disease but most are beneficial-domain Archaea: unicellular, often live in extreme conditions • Prokaryotes have unique cellular structures and properties• nearly all prokaryotes have a cell wall-provides protection in a range of environments• many species are mobile -flagella propel cells• many prokaryotes have a sticky capsule -provides protection and allows cell to stick to surfaces• some prokaryotic species can form an endospore, a thick-shelled protective container forharsh conditions-when conditions improve, the bacteria can resume function• many prokaryotes reproduce by “splitting in half,” a process called binary fission-this can result in a huge population of prokaryotes in a short period of time• prokaryotes living together can form unique features• prokaryotes often form biofilms, organized colonies of one or several species attached toa surface, such as rocks or living tissue • prokaryotes exhibit a wide range of nutritional habits-photosynthesis-consumption of other organisms-can even produce their own food directly from the environment• obtain nutrition from the sulfur-rich superheated water emitted by a hydrothermal vent several kilometers beneath the surface of the ocean• prokaryotes in the domain Archaea are often found in extreme habits • Archaea include:-methanogens (which produce methane gas)-halophiles (salt lovers)-thermophiles (heat lovers)• Methanogens live in anaerobic (oxygen-free) environments• Methanogens emit methane gas• They are frequently found in the thick mud at the bottom of a swamp or bog• Methanogens thrive in the oxygen-free conditions within landfills • Halophiles are archaea that thrive in very salty environments• Archaea are among the few forms of life that can tolerate the high salt concentrations found in the dead sea, Israel • Thermophiles live and grow in high-temperature environments• Thermophiles (“heat lovers”) ca live in areas with temperatures above boiling-conditions may be similar to those faced by the first organisms billions of years ago• Prokaryotes in the domain bacteria are very numerous and common• Bacteria thrive I most of Earth’s habitats-including in and on your body• Bacteria can be harmful or helpful• Each bacterium is microscopic, but their collective impact is enormous • Bacteria have one chromosome and reproduce asexually• Bacteria reproduce by binary fission• Bacteria in a colony are genetically identical to each other• But this does not mean that bacteria lack ways to produce new combinations of genesEukaryotes• For the first 1.4 billion years of life on Earth, prokaryotes were the only ell type• Around 2 billion years ago, the first eukaryotic cells evolved • All cells have 3 things:1. A set of genes2. A plasma membrane3. Cytoplasm containing the metabolic machinery (ribosome)• Endosymbiosis-endo = internal-sym = shared-bio = life• One cell engulfed another cell• Both cells benefit• Engulfed cell has a nice place to live in exchange for energy production• Internal membranes likely evolved from inward folding of the plasma membrane• The mitochondria and chloroplast likely originated from endosymbiosis• The origin of multicellular life was a major milestone in the evolution of life• Biologists hypothesized a series of steps that may have occurred in the evolution of