9/9/2010 CHAPTER 1: BIOLOGY & THE TREE OF LIFE 1.1 Organism: a life-form?a living entity made up of one or more cells? share 5 characteristics Energy?must acquire and use energy Cells?made up of membrane-bound units (cells) Membrane regulates passage of materials between exterior and interior spaces Information?process hereditary or genetic information, encoded in genes, and information acquired from the environment Replication?majority of organism?s functions contribute to one goal: replicating itself Evolution?organisms are the product of evolution, and continue to evolve 1.2 2 great unifying ideas that biology is based off of: cell theory & the theory of evolution Theory: an explanation for a very general class of phenomena or observations Emerged in mid 1800?s Established 2 of 5 attributes of life Organisms are cellular Organisms? populations change over time Cellular History 1665 Robert Hooke microscoped (30X magnification) cork from an oak tree and saw small, pore-like compartments? later called cells Anton van Leeuwenhoek developed much powerful microscope w/ magnification up to 300X Examined pond water and made first observation of human blood cells and sperm cells In 1670?s researcher determined that leaves and stems of plants are composed of many individual cells By 1800 enough data to claim that all organisms consist of cells In 1858 Rudolph Virchow determined that all cells arise from preexisting cells Louis Pasteur did experiment to test the cell from cell vs. spontaneous generation theory Straight necked and curved necked bottles used? cells only grew in straight necked bottle because cells were able to drop into nutrient broth Proved that cell theory was correct Proved that spontaneous generation was false Cell: highly organized compartment that is bounded by a thin, flexible structure called a plasma membrane and that contains concentrated chemicals in an aqueous solution Chemical reactions that sustain life take place inside cells Most cells can reproduce by dividing themselves Cell Theory: All organisms are made of cells, and all cells come from preexisting cells Contradicted previous belief of spontaneous generation Spontaneous was a hypothesis (a proposed explanation) Theory refers to proposed explanations for broad patterns in nature Hypothesis refers to explanations for more tightly focused questions Prediction: something that can be measured and that must be correct if a hypothesis is valid All cells come from preexisting cells all individuals in an isolated population of single-celled organisms are related by common ancestry all cells in a multicultural organism are connected by common ancestry Charles Darwin and Alfred Russel Wallace realized (separately) that all species are connected by a common ancestry 1.3 Theory of Evolution Species are related by common ancestry Characteristics of species can be modified from generation to generation? Darwin called it ?descent with modification? Evolution: a change in the characteristics of a population over time Natural Selection Explains how evolution occurs Occurs when 2 conditions are met Individuals within a population vary in characteristics that are heritable (can be passed on to offspring) Population: a group of individuals of the same species living in the same area at the same time In particular environments, certain versions of these heritable traits help individuals survive better or reproduce more than others Natural selection acts on individuals, but evolutionary change occurs in populations Artificial selection: changes in populations that occur when humans select certain individuals to produce the most offspring First done long-term on corn Evolution occurs when heritable variation leads to differential success in reproduction Fitness: the ability of an individual to produce offspring (higher fitness = more offspring) Adaptation: a trait that increases the fitness of an individual in a particular environment Cell theory and Theory of Evolution provided biology with two central unifying themes: The cell is the fundamental structural unit in all organisms All species are related by common ancestry and have changed over time in response to natural selection 1.4 Speciation: when natural selection causes one species to diverge and form new species All species come from preexisting species All species trace their ancestry back to a common ancestor Tree of Life: A family tree of organisms Phylogeny: the actual genealogical relationships between organisms To understand which organisms are related closely/not so closely, researchers studied a molecule found in all organisms? ribosomal RNA rRNA is made up of four smaller chemical components called ribonucleotides symbolized by the letters A, U, C, and G So useful because the ribonucleotide sequence in rRNA can change during evolution Phylogenic tree shows relationships between species Three fundamental groups or lineages of organisms [DOMAINS] Bacteria Prokaryotes (no nucleus) Most are unicellular Archaea Prokaryotes (no nucleus) Most are unicellular Eukarya Eukaryotes (nucleus) Most are multicellular Taxonomy: the effort to name and classify organisms Taxon: named group Phylum: major lineages within each domain Each is considered a major branch on the tree of life Genus: made up of a closely related group of species Naming species: Carolus Linnaeus, 1735 First part indicates organism?s genus Second term identifies the organism?s species This is called an organism?s scientific name 1.5 Scientists can?t answer questions that can?t be answered by measuring things Science is about formulating hypotheses and finding evidence that supports or conflicts with those hypotheses Hypothesis testing: State the hypothesis as precisely as possible and list the predictions it makes Design an observational or experimental study that is capable of testing those predictions
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