Chapter 1 Biology and the Tree of Life 01 10 2012 Organism a life form a living entity made up of one or more cells no simple definition of life endorsed by all biologists but most agree that organisms share a suite of 5 fundamental characteristics o organisms obtain and use energy o are made up of cells cellularity o process information o replicate reproduce o evolution change over time theory an explanation for a very general class of phenomena or cell theory and theory of evolution established 2 of the 5 attributes of life organisms are cellular and their populations change over time observations Robert Hook 1665 used a crude microscope 30x to examine the structure of cork from an oak tree o cork had small pore like compartments that were invisible to the naked eye structures were called cells Anton van Leeuwen Developed a much powerful microscope 300x Inspected samples of pond water and discovered first human blood cells and sperm cells Cell a highly organized compartment that is bounded by a thin flexible structure called a plasma membrane and contains concentrated chemicals is a aqueous solution Scientific theories have two components A pattern in the natural world A mechanism or process that is responsible for creating that pattern Cell theory all organisms are made up of cells and all cells come from preexisting cells Two hypotheses Hypothesis a proposed explanation Spontaneous generation springing to life from non living materials All cells from cells hypothesis cells do not spring to life spontaneously but are produced only when preexisting cells grow and divide Experiment to test hypothesis Louis Pasteur Prediction something that can be measured and that must be correct if the hypothesis is valid see figure 1 2 on page 3 experimental set up was effective because there was only one difference between the two treatments and because that difference was the factor being testing in this case a broth s exposure to preexisting cells Theory of Evolution by Natural Selection Darwin Wallace papers written separately explaining this Theory has pattern process component Species are related by common ancestry the characteristics of species can be modified from generation to generation descent with modification natural selection explains how evolution occurs o occurs whenever 2 conditions are met individuals within a population vary in characteristics that are heritable traits that can be passed on to offspring in a particular environment certain versions of these heritage traits help individuals survive better or reproduce more than do other versions o natural selections acts on individuals but evolutionary change occurs in populations artificial selection changes in population that occur when humans select certain individuals to produce the most offspring evolution occurs when heritable variation leads to differential success in reproduction fitness the ability of an individual to produce offspring Individuals with high fitness produce many surviving offspring adaption a trait that increases the fitness of an individual in a particular environment Cell theory and theory of evolution provided science of biology with two central unifying ideas 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 Speciation populations of one species to diverge and form new species All species come from preexisting species All species trace their ancestry back to a single common ancestor Tree of life a family tree of organisms Carl Woese analyzed chemical components of organisms as a way to understand theory evolutionary relationships o Goal was to understand phylogeny actual genealogical relationships or all organisms RNA ribonucleotide acid of evolution Ribosomal RNA rRNA is a trait that can change during the course If theory is correct rRNA sequences should be very similar in organisms that are less closely related Species that are part of the same evolutionary lineage should share certain changes in rRNA that no other species have A phylogenic tree shows relationships between species On a phylogenic tree branches that share a recent common ancestor represent species that are closely related branches that don t share a recent common ancestor represent species that are more distantly related Tree of Life Three fundamental groups or lineages of organisms o The Bacteria prokaryote o The Archaea prokaryote o The Eukarya eukaryote Eukaryotes Prokaryotes Nucleus Multicellular many celled Unicellular one celled Taxonomy the effort to name and classify organisms Any named group is called a taxon Woese proposed domain as a new taxonomic category Three domains of life Bacteria Archaea Eukarya Phylum major lineages within each domain Each phylum is considered a major branch on the tree of life Scientific Names Carolus Linneaus established system Each scientific name is unique Often descriptive Two part name unique to each organism o First part genus made up of closely related groups of species o Second part organism s species Example genus homo species sapiens homo sapiens humans The Nature of Science Scientists ask questions that can be answered by measuring things Science is about formulating hypotheses and finding evidence that supports or conflicts with these hypotheses Hypothesis testing is a two step process State the hypothesis as precisely as possible and list the Design an observation or experimental study that is capable of predications it makes testing those predictions Two ways to test hypotheses experimental evidence or observational evidence Experiments are a powerful scientific tool because they allow researchers to test the effect of a single well defined factor on a particular phenomenon Good scientific hypotheses make testable predictions predictions that can be supported and rejected by collecting and analyzing data A null hypothesis specifies what we should observe when the hypothesis being tested isn t correct Important Characteristics of good experimental design Critical to include control groups A group of outside subjects whose performance or abilities are compared with the experimental o Checks for factors other than the ones being tested The experimental conditions must be as constant or equivalent as subjects possible o Eliminates alternative explanations for the results Repeating the test is essential o Repeated in large groups o Amount of distortion in the data caused