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BIOL 1500

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Biology Chapter 10 Notes: The Origin and Diversification Of Life on Earth • how did life on earth begin? Life is defined by the ability to replicate and by the presence of some sort of metabolic activity • Earth formed about 4.5 billion years ago from clouds of dust and gases left over after the formation of the sun; initially super-hot and gradually cooled; first life on earth tolerated an atmosphere without oxygen; atmosphere originally had a large amount of carbon dioxide, nitrogen, methane, ammonia, hydrogen and hydrogen sulfide "Darwin's warm little pond" • Biodiversity: variety and variability among all genes, species and ecosystems on the planet • Multiple suggestions on the start of the first organisms; classified by several distinct phases instead Phase 1: formation of small molecules containing carbon and hydrogen; no oxygen was original present in old rocks; because of the chemical structures, the molecules bond very easily and in many ways; caused them to have huge variety of forms and functions • Stanley Miller and Harold Urey created an environment for the "warm little pond" • A flask of water with H2, CH4 (methane) and NH3 (ammonia); they subjected their mini- world to sparks, to simulate lightning; they cooled the atmosphere so that any compounds formed in it would rain back down into the water; they waited and examined the contents of the water and to see what happened; discovered many organic molecules including 20 different amino acids; promising steps but the ozone in the atmosphere would not have had protection against UV rays that broke down methane and ammonia Phase 2: the formation of self-replicating, information containing molecules; researchers have discovered a molecule that could function as an enzyme that links together nucleic acids (nucleic acid RNA); notable because it means that the single relatively simple molecule could have been self-replicating; supports RNA world hypothesis which proposes that the world may have been filled with RNA-based life before it had DNA-based life; 3.4 billion year old cells have been found in rocks from South Africa; life is typically determined by two characteristics; the ability to replicate and the ability to carry out some sort of metabolism; RNA molecules satisfied the replication but not the metabolism Phase 3: the development of a membrane, enabling metabolism and creating the first cells; membranes make numerous aspects of metabolism possible; they make it possible for chemicals inside the cell to be at higher concentrations than if they were outside the cell which are essential to most life-supporting reactions; suggestions that the first cells may have come together spontaneously; mixtures of phospholipids placed in water/salt solutions tend to spontaneously form small spherical units that resemble living cells; these spontaneous membranes might have formed around a self-replicating molecule creating these microspheres Species & Biodiversity Biological Species: populations of organisms that interbreed or could possibly interbreed with each other under natural conditions and cannot interbreed with organisms outside their own group; instead of physical features, the emphasis goes towards reproductive isolation; just because the individuals are physically separated, they aren't necessarily in different species (could possibly interbreed); conditions are not considered natural when under captivity Prezygotic Barriers: makes it impossible for individuals to mate with each other or for the male's reproductive cell to fertilize the female's reproductive cell; includes situations in which the members of the two species have different courtship rituals or physical differences or biochemical factors Postzygotic Barriers: occurs after fertilization and generally prevent the production of fertile offspring from individuals of the two species; such offspring are called hybrids; either do not survive long or survive and are infertile or have reduced fertility; mules are a hybrid of horses and donkeys and cannot breed with each other or produce offspring Naming Species • important for biologists to order and classify life; uses the system developed by Swedish biologist Carolus Linnaeus in the mid 1700s "Systema Naturae" or "System of Nature" • every species is given a scientific name that consists of two parts; a genus and a specific epithet; Homo-sapiens are humans; the "species" is the narrowest classification for an organism • Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species • plants and animals are referred to by common names but also have their official names in the Linnaen system Not Always Easily Defined • can be biased towards the classifications and decisions • Difficulties classifying asexual species; asexual reproduction does not involve interpreeding, the concept of reproductive isolation is no longer meaningful; might seem that every individual should be considered a separate species • Difficulties classifying fossil species; differences in size and shape of fossil bones cannot reveal whether there was reproductive isolation between the individuals from whom the bones came • Difficulties in determining when one species has changed into another; unsure about what exact point did the certain species turn into another • Difficulties in classifying ring species: two non-interbreeding populations may be connected to each other by gene flow so there is no exact point where one species stops and the other begins; gradual changes in reproductive isolation accumulate so when the populations meet up again, there are sufficient differences physically and behaviourally; green warblers are one of the 20 examples of ring species • Difficulties in classifying hybridizing species: the interbreeding of closely related species; sometimes occurs and produces fertile offspring suggesting that the borders between the species are not clear cut; morphological species concept characterizes species based on physical features such as body size and shape (subjective but can be effectively used to classify some asexual species); does not require the knowledge of whether individuals can actually interbreed How Do New Species Arise? Speciation: the process in which one species splits into two distinct species; occurs in two phases and requires more than just evolutionary change in a population 1. Reproductive isolation: through which two populations come to have independent evolutionary fates 2. Genetic divergence: two populations evolving as separate entities accumulate physical and behavioural differences over time as they become adapted different to features of their separate environments including different predators, types and abundances of food available • Allopatric speciation: Speciation with geographic isolation; over time, the two split populations have different evolutionary paths as they adapt to particular features of their habitats; two populations eventually may genetically diverge enough that if the two species interact again, they might not be able to interbreed; Galapagos Island finches; might be separated through rivers, glaciers or landforms resulting into different environments • Sympatric speciation: speciation without geographic isolation; can also occur among populations that overlap geographically; rare in animal populations but is common among plants; during plant cell division, an error sometimes occurs in which the chromosomes are duplicated but the cell does not divide; doubling of number of sets of chromosomes is called polyploidy; these plants can no longer interbreed with each other but can propagate through self-fertilizations or by mating with other individuals that have the same sets of chromosomes; more common method occurs when plants from different but closely related species interbreed forming hybrids; propagates itself asexually; can ultimately produce fertile individuals ; process of speciation called allopolyploidy • when reproductive separation occurs, new populations are isolated from each other but could potentially still interbreed; speciation is not complete until sufficient differences have evolved in
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