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Biology Chapter 2 Notes

by: Allie Muro

Biology Chapter 2 Notes Biology 114

Allie Muro
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Principles of Biology
Dr. Stevan Marcus

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notes from week of January 18
Principles of Biology
Dr. Stevan Marcus
Class Notes




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This 4 page Class Notes was uploaded by Allie Muro on Monday January 18, 2016. The Class Notes belongs to Biology 114 at University of Alabama - Tuscaloosa taught by Dr. Stevan Marcus in Spring 2016. Since its upload, it has received 18 views. For similar materials see Principles of Biology in Biology at University of Alabama - Tuscaloosa.

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Date Created: 01/18/16
12016 Chapter 2 Organism any contiguous living system such as an animal plant or bacterium o All organisms composed of matter Matter anything that takes up space and has mass 0 All biological matter is composed of elements 0 Element matter that cannot be broken down to other substances by chemical reactions 0 An elements chemical properties depend on the structure of its atoms 0 Atom smallest unit of matter that still retains the properties of an element 0 A compoundis a substance consisting of two or more elements in a xed ratio 0 Has characteristics different from both of its elements 0 Ex sodiumsoft metalchlorinegas sodium chloridecrystalsalt 0 Depending on the organism anywhere from 2025 of the 92 naturally occurring elements are essential to life 0 Oxygen carbon hydrogen and nitrogen make up about 96 of the human body mass 963 0 Trace elements are those required by an organism in relatively minute quantitiescalcium phosphorus potassium sulfur sodium chlorine magnesium 37 Atoms are composed of 3 types of quotlargequot subatomic particles 0 Protons positive charge 0 Neutrons no electrical charge 0 Electrons negative charge Neutrons and protons form the atomic nucleus of an atom Electrons occupy a space around the nucleus of an atom referred to as the electron cloud Proton and neutron mass are almost identical and measured in units called daltons Da 1 Da mass of 1 proton o Electrons are nearly 2000 times smaller in mass than protons and neutrons Protons and neutrons each have a mass of about 167x10quot24 grams or one millionth of a billionth of a gram Electrons have a mass of about 912x10quot28 grams 1800 times less than a proton and thus make an inconsequential contribution to atomic mass 0 Examples to illustrate minuteness of atoms 0 A typical human hair is about 1 million carbon atoms in width 12016 0 A signle drop of water contains about 210quot21 2 billion trillio atoms of oxugen and twice as many atoms of hyrdrogen Chapter 2 Atomic Number and Atomic Mass 0 Atoms of the various elements differ in their number of protons neutrons and electrons Atomic number of protons in nucleus 0 All atoms of an element have the same number of protons Atomic mass protons neutrons in the nucleus 0 Since electrons have a mass more than 3 orders of magnitude gt10quot3 less than a proton atomic mass atoms total mass can be approximated by its atomic number Isotopes All atoms of an element have the same number ofprotons but may differ in the number of neutrons Isotopes of an element have nuclei with the same number of protons same atomic number but different numbers of neutrons Isotopes can be stable or unstable 0 Stable isotopes do not decay 0 Unstable isotopes are called radioactive isotopes or radioisotopes 0 Radioisotopes decay spontaneousy eg uranium to lead giving off gama rays andor subatomic particles ionizing radiation 0 The rate of decay of a radioactive isotope is referred to as its halfife 0 Half life values vary from seconds to days to billions of years 0 All atoms of an element have the same number of protons but may differ in the number of neutrons Isotopes of an element have atomic nuclei with the same number of protons but different numbers of neutrons 0 Examples hydrogen stable atom number 1 atom mass 1 half life NA 0 Tritium not stable atom number1 atom mass3 half life 123 yr Applications of Radioactive Isotopes in Biological Research and Medicine 0 dating fossils o c14 to c12 ratio 0 decay of uranium to lead in zircon ZrSiO4 0 As tracers to follow atoms through metabolism 0 Cells use radioactive isotopes as they would nonradioactive isotopes of the same element 0 Important in medical diagnostics eg PET scans Labeling macromolecules in experimental cell and molecular biology research 0 Radiation from decaying radioisotopes can damage or kill cells The Energy Levels of Electrons Energy capacity to cause change for instance by doing work 0 Potential energy energy that matter has because of its location or structure Electrons of an atom have potential energy because of how they are arranged in relation to the nucleus negatively charged electrons of an atom are attracted to the positively charged nucleus 0 An electrons state of potential energy is called its energy level or electron shell 0 The more distance an electron is from the nucleus of an atom the greater its potential energy 0 Energy is required to move an electron farther away from a nucleus 0 Energy is released when an electron moves to a lower energy shell shell closer to the nucleus 0 Atomic nucleus1st shell lowest energy2nCI shell higher energy3rCI shell highest energy Electron shells For elements whose atoms have no more than 3 electron shells the maximum number of electrons that can occupy each shell are as follow 0 1st shell max of 2 electrons o 2ncl shell l max of 8 electrons 0 3rd shell l max of 8 electrons valence electrons valence electrons are those in the outermost electron shell which is referred to as the valence shell 0 the chemical behavior of an atom is determined primarily by its valence electrons 0 elements with a full valence shell are chemically inert nonreactive 0 maximum number of valence electrons in rst 3 electron shells o lst 2 o 2 8 0 3rd 8 o tend to travel in pairs 0 tend to move toward a full valence shell by 0 adding electrons to the outer shell eg chlorine o losing electrons eg sodium 0 sharing electrons in the outer shell electron orbitals electron orbital 3dimensional space where an electron is found 90 of the time 0 each electron shell consists of a speci c number of orbitals electron orbitals de ne an atoms 3dimensional shape


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