Biology 118 1st Edition Lecture 2 Outline of Last Lecture I. Overview of Syllabus Outline of Current Lecture I. Chapter 1: Biology and the Tree of Lifea. What is life?b. What does it mean to say that something is alive?c. What is a theory?d. Cell Theorye. How do we know cells come from other cells?f. Theory of Evolution by Natural SelectionII. Chapter 2: Water & Carbona. Electron Arrangement around the nucleusb. Chemical Bondingc. How many bonds can an atom have?d. Electronegativity & chemical bondingCurrent LectureWhat is life?- All living organisms share basic fundamental characteristics- The cell theory states that all organisms are comprised of cells- The theory of evolution by natural selection describes how species change over timeWhat does it mean to say that something is alive?- Acquire and use energy- All organisms are made up of membrane bound cells- All organisms process hereditary information encoded in genes, as well as other information from the environment- All organisms are capable of reproduction- Populations of organisms are continually evolvingWhat is a theory?- A theory is an explanation for a very general class of phenomena or observationso Supported by wide body of evidenceThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Most have two parts Pattern-regularities observed in natural world Process-mechanism responsible for creating the patternso Be sure you can distinguish theory from hypothesis o Theories reserved for broad patterns in natureCell Theory- Late 1660’s Robert Hooke and Anton von Leeuwenhoek were first to observe cells- A cell is a highly organized compartment bounded by a plasma membrane that contains concentrated chemicals in an aqueous solution- The cell theory states that:o All cells are made of cells (pattern)o All cells come from preexisting cells (process)How do we know all cells come from other cells?- Two hypotheses:o Spontaneous Generation (1800’s) Cells arise spontaneously under certain conditions (Proved false)o All-cells-from-cells (Virchow’s hypothesis & Pasteur’s experiment) Pasteur’s experiment: Flasks with two different spouts curved spout trapped cells, while the open one allowed cells to penetrate sterile broth Conclusion: all cells come from preexisting cellsTheory of Evolution by Natural Selection- 1858- Charles Darwin & Alfred Russell Wallaceo All species related by common ancestry (pattern)o Characteristics can be modified from generation to generation Descent with modification (process)CHAPTER 2: WATER AND CARBON- Mass number: number of protons + neurons- Atomic number: number of protonsElectron Arrangement Around the Nucleus- Electrons move around atomic nuclei in specific regions called orbitalso Each orbital can hold up to two electrons- Orbitals are grouped into levels called electron shellso Electron shells are numbered, with smaller numbers closer to the nucleuso The electrons in the outermost shell are called valence electrons- Elements commonly found in organisms have at least one unpaired valence electron. The number of unpaired electrons in an atom is its valenceo Valence electrons do not equal valenceChemical Bonding- Unfilled electron orbitals allow formation of chemical bonds and atoms are the most stable when each electron orbital is filledo Covalent Bond: Each atom’s unpaired valence electrons are shared by both nuclei to fill their orbitals Substances held together by covalent bonds are called moleculeso Ionic Bond: Electrons are transferred from one atom to another How many bonds can an atom have?- The number of unpaired electrons determines the number of bonds an atom can make- Atoms with more than one unpaired electron can form multiple single, double or triple bondsElectronegativity & Chemical Bonding - Electronegativity= a measure of the ability of an atom to attract electrons from an atom it is bonded to- Electrons are not always shared equally - An atom with a high electronegativity will hold the electrons more tightly than that with a low electronegativity, and have a partial negative charge, whereas the other atom will have a partial positive
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