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Chapter 1

BIOLOGY 1M03 Chapter 1: Chapter 1

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Ben Evans

Biology and the Tree of Life Key Developments • Cell theory • The theory of evolution by natural selection -both of these developments are unified by concepts of ancestry and descent. Evolutionary relationships among species and among cells can be represented by phylogenetic trees. Five Characteristics of Living Organisms • They are made up of one or more membrane-bound units called cells • They store and process information that is heritable • They replicate (meaning they reproduce) • As populations, they evolve (meaning they change) • They use Energy Cell Theory • A cell is highly organized compartment bounded by a plasma membrane that contains concentrated chemicals in an aqueous solution. All cells have a plasma membrane • The cell theory states that all organisms are made of cells, and all cells come from pre- existing cells • Within a multicellular individual, all cells are descended from a progenitor cell-the zygote • A zygote is also derived from other cells (named an egg and a sperm) Ex. Paramecium in pond water Essential Features of Cells • In general, cells contain molecular information (DNA) that encodes their physical attributes (though some cells lose their DNA) • Cells have a boundary between them and the environment • Cells have the ability to harness materials and/or energy Virus a Living Organism • A virus is an agent that infects cells and uses the cellular machinery of a host to replicate • Viruses have the ability to store and transit information in DNA or RNA • But because viruses cannot independently replicate or independently harness energy, they are not considered to be living organism Testing the Cell Theory • Hypothesis: proposed explanations • Prediction: something that can be measured and must be correct if a hypothesis is valid Ex. Maggots forming Spontaneously on meat Observation: maggots appear in meat when it is left out Hypothesis: flies lay eggs on meat, which grow into maggots Alternative hypothesis: maggots arise spontaneously Maggots in open jar – maggots appeared in open jar Gauze-covered jar – no maggots appeared in the gauze – covered jar Franscisco Redi’s experiment in the 1600’s -First to have controls Microorganisms • About 200 after Redi’s experiment, Louis Pasteur designed a similar experiment to test the cell theory: that all cells arise from other cells • The null hypothesis of this experiment was that cells are not derived from other cells (this is also called spontaneous generation) Step 1: Place Broth capable of supporting life in two types of flask Step 2: Boil to sterilize Step 3: Wait and see what grow in each flask -condensation seals off contents in flask Implications of the Cell Theory • Because all cells come from pre-existing 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 pre-existing ells and are also related by common ancestry • For the nematode Caenorhabditis elegans, we now have a complete map of every cell division from zygote to adult Theory of Evolution by Natural Selection • In 1858, Darwin and Wallace proposed that all species are related by common ancestry • Darwin and Wallace also proposed that the characteristics of species can change from generation to generation Key Terms Evolution: postulates that species are related to one another and species can change through time Natural Selection: is a process that explains how evolution occurs Fitness: is the ability of an individual to produce offspring Adaptation: is a characteristic that increases the fitness of an individual in a particular environment (not all characteristics are are considered to adaptations). It is also the process of a species acquiring fitness-improving traits over time. Natural Selection Must Have… • Variation • Heritable • Influence Fitness -if heritable characteristics lead to increased success in producing offspring, then these traits become more common in the population over time -Natural selection acts on individuals, but evolutionary change affects only populations -evolution occurs when heritable variation leads to differential success in reproduction Artificial Selection • A form of natural selection where humans drive the cours
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