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Scientific Theories and Laws in Biology Mrs. Dignan’s Science Class There are 3 Theories and a Law that support most of what we know about Biology. 1. What is a Scientific Theory? An explanation of something in nature that is widely accepted and heavily supported by experimental data. It has not yet been disproven. 2. What is a a Scientific Law? A description of the way things work in our universe. They are generally much shorter than theories The 1st Law of thermodynamics Matter and energy cannot be created or destroyed. They can change forms, though. 4. Give an example of a reaction where matter changes forms but DOES NOT lose mass. The 1st Law of thermodynamics 5. Describe the energy transformations shown in the picture at right. The Atomic Theory All matter is made of atoms Atoms of one element have unique properties and are identical Atoms of different elements are distinctly different Atoms can bond with other atoms to form compounds The Atomic Theory Atoms are made of smaller particles (protons, electrons, and neutrons) The protons and neutrons have the most mass and occupy the solid nucleus at the center of the atom The electrons orbit around the nucleus at distinct energy levels The Atomic Theory 4. 5. Protons have a positive charge Neutrons have a neutral charge Electrons have a negative charge Draw the model of the carbon atom in your notebook How many electrons are there in the 1st Energy Level? The Atomic Theory 6. Draw a model of an Oxygen atom in your notebook. 7. Draw a model of a Hydrogen atom in your notebook. Cell Theory All living things are made out of at least one cell (some are made of trillions). All cells come from other cells. Cell Theory Cells are able to copy themselves Cells contain special machines in them called “organelles” that carry out operations within the cell. All cells contain DNA, the instructions for making more cells. The Theory of Evolution DNA changes over time through random mutations Some mutations are helpful and are kept Living things change over time Eventually living things can become separate species. The Germ Theory of Disease Validated by Luis Pasteur in the 19th century. All living things come from other living things. All living things will die. Living organisms must enter an closed system in order to grow in it.