Biol 213, Study Guide Exam no 1 (1/2)
Biol 213, Study Guide Exam no 1 (1/2) Biol 213
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This 6 page Study Guide was uploaded by Irvane Ngnie Kamga on Monday February 8, 2016. The Study Guide belongs to Biol 213 at George Mason University taught by James Reid Schwebach (P) in Winter 2016. Since its upload, it has received 99 views. For similar materials see Cell structure and Function in Biology at George Mason University.
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Date Created: 02/08/16
Biol 213 – Exam no1 Study Guide (1/2) Cf. definitions of key words and concepts: https://studysoup.com/george-mason-university/biol- 213/flashcards/biol-213-chap-1&2-key-definitions?id=141776 Chapter 1 1.1. What is Biology? Life arose on earth approximately 4 billion years ago (4.6 to 4.5). There is a single origin of life, one common ancestry to all living organisms. This is supported by many facts: Living organisms are made up of a common set of chemical components, including but not limited to nucleic acids, amino acids, fatty acids, and particular carbohydrates. They contain genetic information that uses a nearly universal code to specify the assembly of proteins. They share similarities among a fundamental set of genes, part of which they pass on to other generations. They can extract energy from the environment and produce biological molecules. They self-regulate their internal environment to maintain homeostasis. The building blocks of most organisms are cells. Earth’s history can be depicted as a 30-day month, where each day represents about 150 million years. In this scale, life occurred the 5 day. It is important to note that the origin of photosynthesis takes up a whole week of life’s timeline (that is to say about 1.05 billion years), before the next important event: the origin of eukaryotes (first unicellular, then multicellular). Our species, Homo sapiens, only appeared around 500,000 years ago. Biologists believe that complex biological molecules first arose through the random physical association of chemicals, a postulate that experiments prove to be probable. There are 3 major domains of life: bacteria, archaea, and eukarya. Eukaryotic organisms actually resulted from the merging of bacteria and archaea. A cell is the principal unit of life. In multicellular organisms, many individual cells serve as the building blocks of tissues and organs. Unlike unicellular prokaryotes, eukaryotes have internal membranes –within their cells –that enclose specialized organelles, including the nucleus. For more than half of Earth’s history, all life was unicellular. Multicellular eukarya evolved from protists, unicellular microbial eukaryotes. ≈ 2.5 B years ago, the emergence of photosynthesis changed the nature of life on Earth. Thanks to its energy-capturing processes (light energy chemical energy), photosynthesis provides food for other organisms, making it the basis of most of life on Earth. It also enabled the accumulation of O (2hich was not present in Earth’s early atmosphere) as photosynthetic prokaryotes increased, which in turn led to the evolution of aerobic organisms. Presence of oxygen in the atmosphere allowed life to arise on land. N.B: aerobic metabolism ›› anaerobic metabolism. 1.2. How Do Biologists Investigate Life? Biologists investigate life through observation, collection of date, experimentation, and logic. They use the scientific method and think critically. The Scientific Method 1. Make observations 2. Ask questions 3. Hypothesize (a good hypothesis is testable and can be refuted) 4. Make predictions based on the hypothesis 5. Experiment to test the hypothesis and one’s predictions 6. Draw a conclusion (do the results support the hypothesis? Does the hypothesis need to be revised/refined?) Inductive logic: observations or facts hypothesis or broader generalization. Deductive logic: general statement or hypothesis predictions about what we should observe if the hypothesis is correct Controlled experiments manipulate one or more of the factors being tested, keeping all other variables constant. They make use of an “experimental” group and a “control” group, and involve an independent variable(s), a dependent variable(s), and sometimes confounding variable(s). Comparative experiments compare unmanipulated data gathered from different sources, noting the similarities and differences. Statistical methods help scientists decide whether the differences measured are significant, that is to say enough to support or falsify a hypothesis. They eliminate –as much as possible – the possibility that the differences showing up in the data are due to random variation. Statistical tests start with a null hypothesis: that no differences exist. Statistical methods (whose purpose is to disprove the null hypothesis) tell us the probability of obtaining a particular result by chance, even if the null hypothesis were true. Generally, differences are said to be significant if the probability of error is 5% or less. Chapter 2 2.1. How Does Atomic Structure Explain The Properties Of Matter? All matter is composed of atoms, units that have a nucleus and 1 or + electron(s) surrounding the nucleus. Electrons negligible mass relative to that of protons or neutrons (9 x 10 g vs. 1.7 x 10 g); negative charge (-e = -1.6 x 10 C)-19 In the nucleus: protons (positive charge, +e) and neutrons (no charge, neutral). The number of protons (atomic number - Z) identifies an element. The number of protons and electrons determine how an element behaves in chemical reactions. Elements are arranged in the periodic table according to their number of protons/electrons, thereby elements in a same column of the periodic table have the same number of electrons on their valence shell. Isotopes are different atoms of a same element: they only differ by their number of neutrons, and therefore their mass number (A). 12 14 Ex: C and C are isotopes. The former has 6 neutrons and the latter 8. However, they both have the same number of protons: 6. The mass number goes at the top and the atomic number at the bottom. Ex: 12 6 C Some isotopes are unstable. Radioactive decay occurs when radioisotopes give off energy in the form of alpha, beta, and gamma radiation from the nucleus. Transforms the atom and sometimes result in a change in element. Radioisotopes can be incorporated into molecules to act as a tag or label. They are useful in research and in medicine. Orbitals describe the locations of electrons. They have characteristic shapes and orientations. They are filled in a specific sequence and occur in a series called electron shells or energy levels: with the exception of the first shell that has 1 s orbital and holds 2 electrons, all additional shell have 4 orbitals and hold 8 electrons. An atom’s valence shell determines how it behaves. Atoms aim to obey either the duet or the octet rule, which leads to chemical reactions. Reactive atoms have unpaired electrons in their valence shell. They can share, lose or gain electrons, resulting in atoms being bonded together to form molecules. 2.2. How Do Atoms Bond To Form Molecules? Chemical Bonds In covalent bonds - which are very stable at temperatures in which life exists and are the strongest type of chemical bonds –atoms share 1 or + pair of electrons. Covalent bonds can be single, double, and even triple. The shape of molecules can change as atoms rotate around a double bond. However, the length, angle and direction of bonds |b| any two elements are always the same. Electronegativity depends on the number of protons and the distance |b| the nucleus and electrons. Polar covalent bonds: electrons are drawn to one nucleus more than to the other because one atom is more electronegative than the other. Partial charges on ≠ ends of the molecule. Ex: H2O is bonded by such bonds, and the Oxygen atom (very electronegative) has a slightly negative charge, while the Hydrogen atoms both have a slightly positive charge. Nonpolar covalent bonds: electrons are shared equally (atoms have similar electronegativity). When one’s atom electronegativity ›› than that of another, a complete transfer of electrons may occur, resulting in two ions with full valence shells. Ex: when a sodium atom (11 electrons) interacts with a chlorine atom (17 electrons), Na yields an electron to Cl so they can both satisfy the octet rule. This results in a sodium cation and a chlorine anion. Ionic attractions: bonds formed by the electrical attraction of positive and negative ions. Salts are ionically bonded compounds. In a solid, ions are close together and the ionic attractions are strong, whereas in water, ions are far apart and the attraction is much weaker because polar water molecules cluster around the cations and anions, preventing them from reassociating. + Hydrogen bonds: bond |b| the δ hydrogen end of one molecule and an electronegative atom of another molecule. Hydrogen bonds form |b| water molecules and are important in the structure of DNA and proteins. Know the ≠ between hydrophilic and hydrophobic molecules. Van der Waals forces: attraction |b| nonpolar molecules that are close together; brief and weak but can be substantial when summed over a large molecule. 2.3. How Do Atoms Change Partners in Chemical Reactions? In a chemical reaction, matter is neither created nor destroyed; everything is transformed. There are reactants and products. Energy is either absorbed (endothermic reaction) or released (exothermic reaction) during chemical reactions. Chemical reactions do not create or destroy energy –the latter is already present in some form (e.g. in the covalent bonds within the molecules) but usually changes form during the reaction. Many reactions in living cells are oxidation-reduction reactions, like that of the combustion of propane (the reducing agent). 2.4. What Makes Water So Important for Life? H 2: polar molecule that forms hydrogen bonds and has a tetrahedral shape. Water has high specific heat, which helps moderate climate and ocean temperatures. It also has a high heat of vaporization, and the heat energy required must be absorbed from the environment in contact w/ the water and results in cooling. Cohesion helps water move through plants and results in surface tension, permitting spiders to walk on the surface of a pond for example. A solution is a substance (solute) dissolved in a liquid (solvent). Many important biochemical reactions occur in aqueous solutions. A qualitative analysis deals with the identification of substances involved in chemical reactions, whereas a quantitative analysis deals with measuring concentrations or amounts of substances. One mole contains 6.02 x 10 molecules (Avogadro’s number). A 1 molar solution is 1 mole of a substance dissolved in water to make 1L of solution. + Acids release hydrogen ions, H , when they dissolve into water. Bases accept them. Strong acids fully ionize in water, whereas weak acids don’t always dissociate into ions. N.B: Acid-base reactions may be reversible, but not when they involve strong acids and bases. Water has a slight tendency to ionize and acts as both a weak acid and a weak base. + The lower the pH, the higher the concentration in H , and thus the greater the acidity. pH influences the rate of biological reactions and can change the 3D structure of biological molecules, impacting their function. That is why organisms use many mechanisms to minimize changes in pH in their cells and tissues. Buffers for example help maintain constant pH. They illustrate the law of mass action: addition of a reactant on one side of a reversible system drives the reaction in the direction that uses up that compound.
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