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Biology and the Tree of Life. Chapter 1. Unity and Diversity of Life. Unity and Diversity of Life. Scope of biology is immense Huge variety of life forms with many diversifying characteristics Two unifying concepts: Cell theory Theory of evolution by natural selection. Cell Theory.
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Biology and the Tree of Life Chapter 1
Unity and Diversity of Life • Scope of biology is immense • Huge variety of life forms with many diversifying characteristics • Two unifying concepts: • Cell theory • Theory of evolution by natural selection
Cell Theory • In the late 1660s, Robert Hooke and Anton van Leeuwenhoek were the first to observe cells. • By the 1800’s there were enough observations to make the generalization that all organisms were made of cells
Cell Theory • The cell theory states that all organisms are made of cells and all cells come from preexisting cells. • Based on inductive reasoning • Hooke and van Leeuwenhoek showed that all organisms are made of cells • Louis Pasteur proved that cells arise from cells and not by spontaneous generation
Cell Theory • Implicated that : • All single-celled organisms in a population are related to a single common ancestor • And all cells in a multi-cellular organism also descend from a single ancestral cell
Theory of evolution by natural selection • In 1858, Darwin and Wallace proposed that all species are related by descent from a common ancestor. • Theory of evolution states that: • Species change over time and are related to one another. • Natural selection is the process by which evolution occurs
Natural Selection • Individuals of the same species living in the same area at the same time constitute a population. • Two conditions must be met for natural selection to occur in a population: • Individuals in the population must differ from one another for some heritable trait(s) • Differential reproductive success due to heritable traits.
Natural Selection • In natural selection, as the individuals with the favorable traits increase in frequency, a population’s characteristics will change over time • In artificial selection, individuals in a population are selected for mating based on particular traits. Repeating this process over generations results in a population with altered characteristics
Artificial Selection • Allows breeding for particular characteristics • Brassica oleracea- broccoli, cabbage, kale, brussell sprouts • All the same species, just different cultivars • Same with dogs and cats
Classifying Life • Linnaeus’ taxonomic system for classifying organisms, each organism is given a unique two-part scientific name consisting of the genus and the species. • Linnaeus’ system is hierarchical with nested taxa. The taxonomic levels from least to most specific are kingdom, phylum, class, order, family, genus, and species
Classification of Organisms • Linnaeus proposed a two kingdom system • Plant and animal • An alternative five-kingdom system based on phylogeny was proposed in the 1960s • Monera, Protista, Animalia, Plantae, and Fungi
Molecular Classification • Carl Woese and colleagues studied small subunit rRNA, as a means for understanding the evolutionary relationships among groups of organisms. • Closely related species should have rRNA sequences that are more similar than those from distantly related species • rRNA sequences can be used to produce a phylogenetic tree
Molecular Classification The tree of life indicates three major groups of organisms: the eukaryotes (Eukarya) and two groups of prokaryotes—the Bacteria and the Archaea. • Woese proposed a new taxonomic level called the domain. Each of the three domains (Bacteria, Archaea, and Eukarya) includes several related kingdoms)
Hypothesis Driven Science • In science, inquiry that asks specific questions involves the proposing and testing of hypothetical explanations, or hypotheses • A hypothesis is a tentative answer to a well-framed question, an explanation on trial • Makes predictions that can be tested
Hypothesis-Driven Science • Example: • Hypothesis: All human males have a Y sex chromosome. • Prediction: If this hypothesis is correct, • Experiment: and I test all human males, • Predicted result: these males should have the Y sex chromosome.
Observations Questions Hypothesis # 1:Dead batteries Hypothesis # 2:Burnt-out bulb Prediction: Replacing bulb will fix problem Prediction: Replacing batteries will fix problem Test prediction Test prediction Test does not falsify hypothesis Test falsifies hypothesis Example: Dead Batteries
Hypothesis Driven Science • A scientific hypothesis must have two qualities • It must be testable • It must be falsifiable • Is an idealized process of inquiry • No amount of testing can prove a theory beyond a shadow of a doubt • Most scientific endeavors do not follow the scientific method to the letter • Often the research gets redirected or changed all together
Experimental Design • A good scientific experiment must have three parts • A control group to check for other factors that might influence the results; • experimental conditions that are controlled to eliminate extraneous variables; • the test is repeated to reduce the effects of random variation (sample size).
