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 Life a What is life b What does it mean to say that something is alive c What is a theory d Cell Theory e How do we know cells come from other cells f Theory of Evolution by Natural Selection II Chapter 2 Water Carbon a Electron Arrangement around the nucleus b Chemical Bonding c How many bonds can an atom have d Electronegativity chemical bonding Current Lecture What 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 time What 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 evolving What is a theory A theory is an explanation for a very general class of phenomena or observations o Supported by wide body of evidence These 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 patterns o Be sure you can distinguish theory from hypothesis o Theories reserved for broad patterns in nature Cell 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 cells Theory of Evolution by Natural Selection 1858 Charles Darwin Alfred Russell Wallace o 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 protons Electron Arrangement Around the Nucleus Electrons move around atomic nuclei in specific regions called orbitals o Each orbital can hold up to two electrons Orbitals are grouped into levels called electron shells o Electron shells are numbered with smaller numbers closer to the nucleus o 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 valence o Valence electrons do not equal valence Chemical Bonding Unfilled electron orbitals allow formation of chemical bonds and atoms are the most stable when each electron orbital is filled o 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 molecules o 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 bonds Electronegativity 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 charge
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