Chapter 3-Exploring the Diversity of Life

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Biological Sciences
Zachariah Campbell

Chapter 3 Selection Biodiversity and Biosphere31 BiodiversityGrouping Organisms How organisms obtain carbon oAutotrophs selfnourishment most plants are autotrophs which synthesize organic carbon molecules using inorganic carbonoHeterotrophs all animals are heterotrophs meaning that they obtain carbon from organic molecules either from living hosts or from organic molecules in the products wastes or remains of dead organismsoOrganisms are also divided according to the source of the energy they use to drive biological activitiesoChemotrophs chemicalnourishment obtain energy by oxidizing inorganic or organic substancesoPhototrophs obtain energy from light32 SelectionSelection occurs whenoSome force or phenomenon affects the survival of individual organisms Ex an unexpected spring frost can kill many plants in your garden Only the coldresistant plants survive the selective force temperatureoA large population of individuals is exposed to a lethal factor and only resistant individuals survive to reproduce If resistance is inherited then the offspring of survivors will be resistantThe key factors behind selection are a selective force pressure and the capacity for explosive population growth When these factors overlap we can be overrun by pests such as antibioticresistant bacteria When this happens the consequences for humans can be deadlySelection is the major force responsible for evolution and biodiversity33 EvolutionEvolution a gradual change in the characteristics of a population of organisms over time can be the result of selectionEvolution is a central key to understanding the diversity of life on earthWe consider evolution to be an organizing force in life and the foundation of modern biologyThe theory of evolution explains both the unity and the diversity of all lifeoIt tells us that all organisms alive today descended from a common ancestorThis explains why all organisms shape features such as the use of ATP as a cellular energy source DNA as genetic material and plasma membranes composed of lipid bilayers Evolution also tells us that species change over time as a result of natural selectionThe central ideas of Darwins theory of evolution by natural selection can be summarized as followsoIndividual organisms in a population vary in many heritable traitsoAny population has the potential to produce far more offspring than the environment can support Competition for limited resources means that only some individuals surviveoSome individuals in the population have traits that give them an advantage in their local environment these organisms are more likely to survive and reproduceoThese organisms pass on favorable traits to their offspring Over time the incidence of the traits will change in the population Different environments favor different traitsoEven though all organisms share a common ancestor they have diverged over evolutionary time in response to the selection pressures of different environments oThe process of adaptive radiation is an example of such divergenceAdaptive Radiation Diversification of Lineages of LifeoIn the history of life on earth organisms have had to overcome fundamental barriers that once crossed opened many new opportunities for diversificationoEx The development of photosynthesis Organisms with the ability to convert solar energy into usable chemical energy survived and thrived as they exploited the new energy source oAdaptive radiations occur when an evolutionary breakthrough allows diversification of life
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