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Chapter 1

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Biology and the Tree of Life Key Concepts  Biological science was founded partially with the development of the cell theory and the theory of evolution by natural selection.  A phylogenetic tree is a diagram that may be interpreted as a graphical representation of inferred evolutionary relationship[s among species. Phylogenies can be established by analyzing similarities (and differences in traits  Biologists ask questions, generate hypotheses to answer them, and design experiments that test the predictions made by competing hypotheses. Scientific Theories  Most scientific theories comprise of two components: o Patterns observed in the natural world o Processes identified that produce the patterns The Cell Theory  In the late 1660s, Robert Hooke and Anton van Leeuwenhoek were the first scientists to observe cells  Cell: a highly organized compartment bounded by a plasma membrane that contain concentrated chemicals in an aqueous solution.  Cell Theory: states that all organisms are made of cells and all cells come from preexisting cells. (Figure 1.1) Louis Pasteur’s Experiment  Hypothesis: a proposal  Prediction: something that can be measured and must be correct if a hypothesis is valid  Louis Pasteur: demonstrated that cells arise from cells and not by spontaneous generation o Pasteur achieved this via an effective experimental setup (Figure 1-2) Implications of the Cell Theory  Because all cells come from preexisting cells, all individuals in a population of single-celled organisms are related by common ancestry.  In a multicellular organism, all of the cells present descend from preexisting cells and are connected by common ancestry Orgins of Life  Current ideas for the orgin of life include models wherein cell based life emerged from matter (molecules)  The Theory of Evolution by Natural Selection  In 1858, Darwin and Wallace proposed that all species are related by common ancestry.  Darwin and Wallace also propsosed that the characteristics of species can be modified from generation to generation. Key Terms  Evolution: entails that species are related to one another and can change through time.  Natural selection: a process that explains how evolution occurs.  Fitness: may be concetualised as the ability of a typical individual (i.e within a group) to survive and produce offspring.  Adaption: (at the microscopic scale) may refer to a trait that increases the fitness of a typical individual in a particular environment. Natural Selection and Populations  Population: a group of indivuduals of the same species living in the same area.  Two conditions must be met for natural selection to occur in a population: o Individuals in the population vary among themselves in characteristics that are heritable o In a particualr environment, certain versions of these heritable traits help individuals survive better or reproduce more than do other versions.  If certain heritable traits lead to increased success in surviving and producing offspring, then these tratis become more common in the population over time. Evolutionary Change  Natural selection acts on individuals, but evolutionary change affects only populations.  Evolution occurs when heritable variation leads to diffe
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