biology-class-12-unit-07-chapter-01genetics-and-evolution-concepts-summary-and-evolution-l-1-3-m6jfohjndyu

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<h3 id="successevolutionsuccess"><Success>Evolution</Success></h3>
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<ul>
<li>What will you learn?</li>
<li>About the process of Evolution</li>
<li>Beginning of Universe and Origin of life</li>
<li>Various theories for origin of life</li>
<li>Theory of use and disuse of organs</li>
<li>Theory of Natural Selection</li>
</ul>
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<h3 id="successthe-primitive-earthsuccess"><Success>The primitive earth</Success></h3>
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<ul>
<li>Earth was not inhabitable when it was formed</li>
<li>There was no atmosphere</li>
<li>No free oxygen</li>
<li>Reducing environment with presence of gases like water vapour, methane, Carbon dioxide and ammonia</li>
<li>UV rays and ionising radiations of sun could easily enter</li>
<li>Very high temperature due to volcanic eruptions</li>
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<h4 id="successoparin-haldane-theory-of-chemical-evolutionsuccess"><Success>Oparin-haldane theory of chemical evolution</Success></h4>
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<ul>
<li>Formation of life was preceded by chemical evolution</li>
<li>Oparin and Haldane of England proposed that first form of life could have come from pre existing non living organic molecules like RNA, proteins etc.</li>
<li>“The hot dilute soup” as described by Haldane suggests that the conditions present on primitive earth was suitable for the synthesis of carbohydrates, fats, amino acids and other complex organic substances.</li>
<li>This synthesis probably occured in sea</li>
<li>The simple organic molecules further polymerised to form complex organic molecules</li>
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<h4 id="successexperimental-evidence-for-chemical-theory-of-evolutionsuccess"><Success>Experimental evidence for chemical theory of evolution</Success></h4>
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<ul>
<li>Stanley Miller and Harold Urey, in 1953 created conditions similar to primitive earth in a laboratory scale</li>
<li>They observed formation of amino acids</li>
<li>Formation of sugars, nitrogen bases, pigments and fats were also observed in other similar experiments</li>
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<h3 id="successorigin-of-cellular-formssuccess"><Success>Origin of cellular forms</Success></h3>
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<ul>
<li>Coacervates - Large colloidal particles called ‘coacervates’ were formed due to tendency of organic macromolecules to aggregate</li>
<li>Microspheres - Membrane bound spheres that appear cell like and could undergo fission and budding</li>
<li>The first membrane bound cells were formed by spontaneous assembly of phospholipid molecules.</li>
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<h3 id="successso-what-exactly-is-evolutionsuccess"><Success>So, what exactly is evolution?</Success></h3>
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<ul>
<li>Biological Evolution is ‘descent with modification’</li>
<li>It refers to the process of gradual changes in an organism over a period of time in response to the environmental changes</li>
<li>Evolutionary Biology is the study of history of life forms on earth</li>
<li>Evolutionary theory deals with how life changed after its origin</li>
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<h3 id="successtheories-of-evolutionsuccess"><Success>Theories of evolution</Success></h3>
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<ul>
<li>Theory of ‘use and disuse of organs’ or the Theory of ’the inheritance of acquired characteristics’ -</li>
<li>Given by Jean Baptiste de Lamarck in 1809</li>
<li>According to his theory -
<ul>
<li>Organisms have needs</li>
<li>Modification of an old organ or formation of a new one is the result of a new need</li>
<li>If an organ is used continuously, it develops. On the other hand, its disuse results in its degeneration</li>
<li>These changes which are brought about during the life of an individual becomes hereditary</li>
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</li>
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<h3 id="successcriticism-of-lamarcks-theorysuccess"><Success>Criticism of Lamarck’s theory</Success></h3>
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<ul>
<li>According to this theory, a new need gave rise to new organs. Man has for long desired to fly but has not developed wings</li>
<li>It states that continuous use of organs makes it highly developed. But many a times evolution shows exactly the opposite, for instance, people who read continuously tend to have redüced eye vision with age</li>
<li>The characters acquired by an organism as a response to the environment is temporary and can not be inherited</li>
<li>Though this theory was not accepted, it was the first truly mechanistic theory of evolution</li>
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<h4 id="successfather-of-evolution---charles-darwinsuccess"><Success>Father of evolution - Charles Darwin</Success></h4>
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<ul>
<li>In 1831, he went on a sea voyage in a ship called H.M.S.Beagle round the world</li>
<li>He made certain interesting observations through this voyage of 5 years</li>
<li>He concluded that all existing life forms shared similarities to varying degrees not only among themselves but also with life forms that existed million years ago</li>
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<h4 id="successwork-of-thomus-malthus-on-population-influenced-darwinsuccess"><Success>Work of Thomus Malthus on population influenced Darwin</Success></h4>
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<ul>
<li>Theoretically, population size will grow exponentially if everybody produced maximally</li>
<li>The fact, that population sizes in reality are limited, means that there had been competition for resources</li>
<li>Only some survived and grew at the cost of others that could not flourish</li>
<li>Darwin asserted that variations, which are heritable and make resources utilization better for few, will enable only those to reproduce and leave more progeny.</li>
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<h3 id="success-alfred-russel-wallacesuccess"><Success> Alfred Russel Wallace</Success></h3>
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<ul>
<li>Made observations similar to that of Charles Darwin during his voyage to Malay archipelago</li>
<li>In 1858, he formulated his theory in an essay form</li>
<li>All existing life forms share similarities and share common ancestors</li>
<li>These ancestors were present at different periods in the history of earth</li>
<li>Geological history of earth closely correlates with biological history of earth</li>
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