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BIOLOGY 1A03 (168)
Chapter 1

Biology Chapter 1.docx

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Lovaye Kajiura

Biology Chapter 1: Biology and the Tree of Life  Most scientific theories have to components o First describes a pattern in the natural world o Second identifies a mechanism or process that is responsible for creating that pattern The Cell Theory  All organisms are made up of cells  Cells are the smallest unit of life  All cells come from pre-existing cells  1665 Robert Hooke examined structure of a cork (bark tissue) from an oak tree under a microscope o Observed small, pore-like compartments invisible to the naked eye, later named cells  Anton van Leeuwenhoek inspected samples of pond water and made the first observations of single-celled organisms (ex. Paramecium) o Also observed and described structure of human blood cells and sperm cells  Cell o A highly organized compartment that is bounded by a thin, flexible structure called a plasma membrane and that contains concentrated chemicals in an aqueous solution  Proposed theory before was that of spontaneous generation  Louis Pasteur created an experiment to test both theories o Created two treatment groups, broth exposed to a source of pre-existing cells and a broth that wasn’t o Both treatments were identical in every way except one  Same glass flasks filled with same amount of nutrient broth and boiled for same amount of time to kill any existing organisms  One flask had a straight neck and the other had a swan neck o Flask with straight neck filled with cells, flask with swan neck trapped pre- existing cells in neck, leaving broth sterile o Therefore the spontaneous generation hypothesis was rejected  Success of cell theory had an important implication o All individuals in a population of single-celled organisms are related by common ancestry Theory of Evolution by Natural Selection  Natural selection occurs when two conditions are met o Individuals within a population vary in characteristics that are heritable (traits can be passed on to offspring)  Population  A group of individuals of the same species living in the same area at the same time o In a particular 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 producing offspring, then those traits become more common in population over time  Population’s characteristics change as a result of natural selection acting on individuals  Natural selection acts on individua
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