MULTIPLE CHOICE Choose the one alternative that best completes the statement or answers the question 1) The smallest stable units of matter are 1) _ A) molecules B) neutrons C) atoms D) electrons E) protons 2) The "atomic number" of an atom is determined by the number of it has A) protons + neutrons B) electrons C) protons + electrons D) protons E) neutrons 2) _ 3) The "atomic weight" of an atom reflects the average number of A) electrons B) protons C) protons + neutrons + electrons D) neutrons E) protons + neutrons 3) _ 4) One mole of any element A) has the same number of electrons B) has the same mass C) has the same weight D) has the same number of atoms E) All of the answers are correct 4) _ 5) The nucleus of an atom consists of A) protons + neutrons B) protons C) protons + electrons D) electrons E) neutrons 5) _ 6) Isotopes of an element differ in the number of A) neutrons in the nucleus B) electrons in energy shells C) electrons in the nucleus D) protons in the nucleus E) electron clouds 6) _ 7) The mass number represents the number of A) electrons in an ion B) protons + neutrons C) neutrons + electrons D) protons in an atom E) neutrons in an atom 7) _ 8) The innermost electron shell in an atom holds up to electrons 8) _ A) B) C) D) E) 9) Radioisotopes have unstable A) isotopes B) protons C) nuclei D) electron clouds E) ions 9) _ 10) By weight, which element is the most plentiful in the human body? A) sodium B) sulfur C) oxygen D) potassium E) carbon 10) 11) Indicate which of these lists contains only trace elements A) selenium, hydrogen, calcium B) sulfur, chlorine, oxygen C) cobalt, calcium, sodium D) silicon, fluorine, tin E) boron, oxygen, carbon 11) 12) The atomic number represents the number of A) electrons in an atom B) neutrons in an atom C) protons in an atom D) chemical bonds the atom may form E) protons and neutrons in an atom 12) 13) Helium (He) has an atomic number of It is chemically stable because it A) is neutral in electrical charge B) will form a covalent bond with another He atom C) readily ionizes to react with other atoms D) lacks electrons, thus the He atom is stable E) has a full outer electron shell 13) 14) Which element commonly has only a proton as its nucleus? A) argon B) hydrogen C) carbon 14) D) helium E) neon 15) By weight, which element is the second most abundant in the human body? A) calcium B) oxygen C) hydrogen D) nitrogen E) carbon 15) 16) The mass of an atom is largely determined by the number of it has A) protons B) electrons C) neutrons D) protons + neutrons 16) E) protons + electrons 17) If an isotope of oxygen has protons, 10 neutrons, and electrons, its mass number is A) 12 B) 16 C) 18 D) E) 26 17) 18) If an element is composed of atoms with an atomic number of and a mass number of 14, then a neutral atom of this element contains A) protons B) electrons C) neutrons D) protons and electrons E) protons and neurons 18) 19) The molecule NO is known as A) nitrous oxide B) nitric oxide C) nitric oxygen D) noxious oxygen E) noxious oxide 19) 20) The molecule CO2 is known as 20) A) B) C) D) E) carbon monoxide carbonated oxygen carbonized oxygen carbon dioxide carbon oxide 21) The molecule H2 is known as A) B) C) D) E) 21) helium hydrohydrogen hydrogen hydroxide semi-water 22) When electrons are transferred from one atom to another, and the two atoms unite as a result of the opposite charges, A) an ionic bond is formed B) a molecule is formed C) an ion is formed D) a hydrogen bond is formed E) a covalent bond is formed 22) 23) Magnesium atoms have two electrons in the outermost shell As a result, you would expect magnesium to form ions with a charge of A) +1 B) -2 C) +2 D) -1 E) either +2 or -2 23) 24) Which of the following statements about hydrogen bonds is false? A) Hydrogen bonds are responsible for many of the properties of water 24) B) Hydrogen bonds are strong attractive forces between hydrogen atoms and negatively charged atoms C) Hydrogen bonds can form between neighboring molecules D) Hydrogen bonds can occur within a single molecule E) Hydrogen bonds are important for holding large molecules together 25) The molecule O2 is known as A) organic B) oxide 25) C) oxate D) a salt E) oxygen 26) H2O is an example of a(n) A) covalent formula B) ion C) glucose molecule D) compound E) ionic formula 27) Which of the following is not a cation? A) Ca2+ B) Na+ 26) 27) C) Cl- D) K+ E) Mg2+ 28) A dust particle floating on a water surface illustrates A) hydrophilic attraction B) chemical tension C) surface tension D) heat capacity E) static electricity 28) 29) In an aqueous solution, cations are attracted toward A) salt B) hydrogen ions C) buffers D) anions E) sodium 29) 30) In an aqueous solution, sodium ions would move toward A) a negative terminal B) a positive terminal C) the bottom D) a pH terminal E) an organic terminal 30) 31) The chemical behavior of an atom is determined by A) the outermost electron shell B) the number of protons C) the mass of the nucleus D) the size of the atom E) the number of neutrons 31) 32) Ions with a + charge are called A) cations B) isotopes C) radicals D) positrons 32) E) anions 33) The weakest bond between two atoms is the bond A) ionic B) hydrogen C) covalent D) polar E) nonpolar 33) 34) When atoms complete their outer electron shell by sharing electrons, they form A) hydrogen bonds B) cations C) anions D) covalent bonds E) ionic bonds 34) 35) Ionic bonds are formed when A) hydrogen forms bonds with negatively charged atoms B) an electron or electrons are completely transferred from one atom to another C) atoms share electrons D) two or more atoms lose electrons at the same time E) a pair of electrons is shared unequally by two atoms 35) 36) If a pair of electrons is unequally shared between two atoms, a(n) occurs A) double covalent bond B) polar covalent bond C) triple covalent bond D) single covalent bond E) hydrogen bond 36) 37) Elements that have atoms with full outer shells of electrons A) will normally form cations B) frequently form hydrogen bonds C) will normally form anions D) are inert gases E) will form many compounds 37) 38) Ions in an ionic molecule are held together due to A) the presence of water molecules B) the sharing of electrons C) each electron orbiting all of the ions in the molecule D) the attraction of similar charges of the ions' protons E) the attraction of opposite electrical charges 38) 39) An unequal sharing of electrons results in what type of chemical bonds? A) hydrogen B) ionic C) covalent D) polar covalent E) peptide 39) 40) Sodium (Na) has an atomic number of 11 How many electrons are in the outer electron shell of a neutral sodium atom? 40) _ _ A) B) C) D) E) 41) Oxygen (atomic number 8) requires how many additional electrons to fill its outer electron shell? A) B) C) D) E) 41) 42) The formula for methane gas is CH4 What does the formula 4CH4 represent? 42) A) B) C) D) E) molecules, each containing a carbon atom and hydrogen atoms a molecule with carbon atoms and 16 hydrogen atoms an inorganic compound with ionic bonds a molecule with carbon atoms molecules, each containing a carbon and a hydrogen atom 43) In an ionic bond, the electron donor is the , whereas the electron acceptor is the A) salt, ion B) cation, anion C) anion, cation D) base, acid E) acid, base 43) 44) In a molecule of nitrogen, three pairs of electrons are shared by two nitrogen atoms The type of bond that is formed is an example of a(n) A) double divalent bond B) triple covalent bond C) single trivalent bond D) hydrogen bond E) polar covalent bond 44) 45) In chemical notation, the symbol Ca2+ means A) a calcium ion that has lost two electrons B) a calcium ion that has lost two protons C) a calcium ion that has gained two protons D) two calcium atoms E) a calcium ion that has gained two electrons 45) 46) Magnesium atoms have two electrons in the outermost shell and chlorine atoms have seven The compound magnesium chloride would contain A) magnesium and chlorine B) magnesium and chlorine C) magnesium and chlorine D) magnesium and chlorine E) impossible to tell without more information 46) 47) AB → A + B is to decomposition as A + B → AB is to A) combustion B) replacement C) synthesis D) metabolism E) exchange 47) 48) The reaction N2 + H2 → NH3 is an example of a(n) A) B) C) D) E) 48) metabolic reaction decomposition reaction exchange reaction synthesis reaction enzyme reaction 49) The reaction A + B + energy → AB is an example of a(n) A) endergonic reaction B) exergonic reaction C) equilibrium reaction D) exchange reaction E) decomposition reaction 49) 50) In hydrolysis reactions, compounds react with A) glucose, causing decomposition B) hydrogen, causing decomposition C) water, causing decomposition D) water, causing synthesis E) carbon, causing decomposition 50) 51) Which one of the following statements is not correct about the reaction H2 + Cl2 → HCl? 51) A) One molecule of hydrogen contains two atoms B) H2 and Cl2 are the reactants C) This reaction is easily reversible D) HCl is the product E) Two molecules of HCl are formed in the reaction 52) In dehydration synthesis reactions, compounds A) gain water molecules B) convert water molecules to hydrogen and oxygen C) gain electrons D) lose water molecules E) convert hydrogen and oxygen to water 52) 53) In the reaction listed below, what coefficient needs to be added to balance the equation? CO2 + H2O → C6H12O6 + O2 53) A) B) C) D) E) 10 54) Chemical reactions that yield energy, such as heat, are said to be A) exergonic B) thermonuclear C) neutral D) activated E) endergonic 54) 55) All of the following are true concerning enzymes, except that they A) function as biological catalysts B) lower the activation energy required for a reaction C) are consumed during the reaction D) affect only the rate of a chemical reaction 55) E) are proteins 56) Compounds that can be synthesized or broken down by chemical reactions inside the body are called A) enzymes B) inorganic compounds C) nutrients D) metabolites E) organic compounds 56) 57) Each of the following is an example of an inorganic compound, except A) carbohydrates B) bases C) salts D) acids E) water 57) 58) Identify which of the following is both an anion and a compound: A) Na+ B) HCO3C) ClD) NaCl 58) E) K+ 59) Nonpolar organic molecules are good examples of A) solutes B) electrolytes C) molecules that will dissociate when placed into water D) hydrophobic compounds E) hydrophilic compounds 59) 60) During ionization, water molecules disrupt the ionic bonds of a salt to produce a mixture of ions These ions can carry a current and so are called A) electrolytes B) acids C) anions D) counterions E) cations 60) 61) Oppositely charged ions in solution are prevented from combining by A) water's nonpolar nature B) hydration spheres C) hydrogen bonding D) free radicals E) heat capacity of water 61) 62) An example of an inorganic substance is A) water and carbon dioxide B) water C) carbon dioxide D) fructose E) glycerol 62) 63) Hydrophilic molecules readily associate with A) hydrophobic molecules B) water molecules 63) C) acids D) lipid molecules E) salts 64) Which of the following statements about water is not correct? A) It is composed of polar molecules B) It has a relatively low heat capacity C) It is responsible for much of the mass of the human body D) It contains hydrogen bonds E) It can dissolve many substances 64) 65) Which property of water helps keeps body temperature stabilized? A) thermal inertia B) kinetic energy C) surface tension D) reactivity E) lubrication 65) 66) Of the list below, which has the highest concentration of hydroxide ions? A) pH B) pH 14 C) pH D) pH E) pH 10 66) 67) Which pH is closest to normal body pH? A) pH B) pH E) pH 67) C) pH D) pH 68) A(n) removes hydrogen ions and a(n) releases hydrogen ions A) element; compound B) molecule; acid C) base; acid D) compound; element E) acid; base 68) 69) An excess of hydrogen ions in the body fluids can have fatal results because this can A) change the shape of large complex molecules, rendering them nonfunctional B) change body fluid pH C) disrupt tissue functions D) break chemical bonds E) All of the answers are correct 69) 70) A solution containing equal numbers of hydrogen ions and hydroxide ions is A) basic B) in equilibrium C) acidic D) alkaline E) neutral 70) 71) The chemical notation that indicates concentration is represented as A) || B) () C) D) [ ] E) {} 72) If a substance has a pH that is greater than 7, it is A) acidic B) alkaline C) neutral E) a buffer 73) Which pH of the following is the most acidic? 71) 72) D) a salt 73) A) pH B) pH C) pH D) pH E) pH 74) Which pH of the following is the least acidic? A) pH B) pH C) pH D) pH E) pH 74) 75) An important buffer in body fluids is A) H2O 75) B) NaOH C) NaCl D) NaHCO3 E) HCl 76) Which of the following substances would be most acidic? A) stomach secretions, pH = B) urine, pH = C) lemon juice, pH = D) tomato juice, pH = E) white wine, pH = 76) 77) Of the following choices, the pH of the least acidic solution is A) 1.0 B) 4.5 C) 6.0 D) 2.3 77) E) 12.0 78) Which has the greater concentration of hydrogen ions, a substance with a pH of or a substance with a pH of 4? A) A pH of is greater B) A pH of is greater C) They are both equal; and are relative values D) pH 9, if you mixed the solutions E) There is not enough information to determine 78) 79) In the body, inorganic compounds A) are structural components of cells B) can make up proteins C) can serve as buffers D) are metabolized for cellular energy E) are made from organic compounds 79) 80) When placed in water, an inorganic compound dissociates 99 percent, forming hydrogen ions and anions This compound would be A) a strong base B) a weak base C) a weak acid D) a salt E) a strong acid 80) 81) When a small amount of HCl or NaOH is added to a solution of Na 2HPO4, the pH of the 81) solution barely changes Based on these observations, all of the following are true concerning the compound Na2HPO4, except A) Na2HPO4 adsorbs excess H+ and OH- directly onto the surface of its crystalline structure B) Na2HPO4 acts as a buffer C) Na2HPO4 is able to accept extra hydrogen ions from the HCl D) Na2HPO4 is able to donate hydrogen ions to the OH- from NaOH E) Na2HPO4 is a salt formed from reacting a strong base with a weak acid 82) Carbohydrates, lipids, and proteins are classified as A) salts B) inorganic molecules C) organic molecules D) acids E) bases 82) 83) A functional group is best described as reoccurring clusters of A) atoms that greatly influence the chemical properties of molecules they are part of B) elements that form at high pH C) atoms that function in the body D) amino acids in a globular protein E) elements that occur in a salt 83) 84) Artificial sweeteners A) are usually not broken down by the body B) are always some form of carbohydrate C) provide the same number of calories as an equivalent amount of sucrose D) are naturally similar to sugars E) are inorganic sugar substitutes 84) 85) Fructose is A) a carbohydrate B) a hexose C) found in male reproductive fluids D) an isomer of glucose E) All of the answers are correct 85) 86) Molecules that have the same molecular formula but different structural formulas are called A) isotopes B) isozymes C) isomoles D) isotypes E) isomers 86) 87) The most important metabolic fuel molecule in the body is A) protein B) sucrose C) glucose 87) D) caffeine E) vitamins 88) A polysaccharide that is formed in liver and muscle cells to store glucose is A) lactose B) sucrose C) fructose D) cellulose E) glycogen 88) 89) The group of organic compounds containing carbon, hydrogen, and oxygen in a near 1:2:1 ratio is defined as a A) carbohydrate B) lipid 89) C) protein D) saturated fat E) nucleic acid 90) An example of an organic substance is: A) sodium chloride B) nitric oxide C) carbonic acid D) sucrose E) oxygen 90) 91) Carbohydrate molecules A) form the regulatory molecules known as enzymes B) are composed of C, H, O, and N atoms C) contain the genetic information found in cells D) are the body's most readily available source of energy E) are the building blocks of cellular membranes 91) 92) When two monosaccharides undergo a dehydration synthesis, A) two new monosaccharides are formed B) a disaccharide is formed C) hydrolysis occurs D) a polysaccharide is formed E) a starch is formed 92) 93) To bond two monomers together, a molecule of water must be to/from from monomers This process is called A) added; hydrolysis B) removed; crenation C) added; denaturation D) removed; dehydration synthesis E) added; ionization 93) 94) Lipids A) form essential structural components of cells B) cushion organs against shocks C) help to maintain body temperature D) provide a significant energy reserve E) All of the answers are correct 94) 95) A fatty acid that contains two or more double covalent bonds is said to be A) polyunsaturated B) hydrogenated C) saturated D) monounsaturated E) carboxylated 95) 96) Alaska Natives have a lower incidence of heart disease even though their diets are high in fat and cholesterol This may be due to the large amount of in their diets A) vitamins B) prostaglandins C) omega-3 fatty acids 96) D) triglycerides E) oleic acid 97) Which of the following is/are needed to form a triglyceride molecule? A) glycerol molecules B) glycerol molecules and fatty acid molecules C) fatty acid molecules and glycerol molecule D) glycerol molecule E) fatty acid molecules 97) 98) A shortage of steroids in the body would result in a shortage of A) proteins B) glycogen C) sex hormones and plasma membranes D) sex hormones E) plasma membranes 98) 99) Most of the fat found in the human body is in the form of A) cholesterol B) prostaglandins C) monoglycerides D) triglycerides E) phospholipids 99) 100) Lipids that are produced by nearly every tissue in the body and act as local regulators are the A) phospholipids B) glycolipids C) steroids D) monoglycerides E) prostaglandins 100) _ 101) Cholesterol, phospholipids, and glycolipids are examples of A) structural lipids B) lipid drugs C) dietary fats D) prostaglandins E) steroids 101) _ 102) A fatty acid with no double bonds between carbon atoms is A) polyunsaturated B) saturated C) denatured D) dehydrated E) unsaturated 102) _ 103) Lipids are composed of fatty acids and A) polypeptides B) glycerol C) amino acids D) monosaccharides E) sugars 103) _ 104) The monomers of protein are A) fatty acids B) nitrogen base C) glucose D) nucleotides E) amino acids 105) Substrate molecules bind to enzymes at the sites A) carboxyl B) amino C) neutral 104) _ 105) _ D) reactant E) active 106) You would expect a peptide bond to link A) two simple sugars B) two nucleotides C) a sugar and a peptide D) two amino acids E) a peptide and a fatty acid 106) _ 107) Each amino acid differs from another in the A) size of the amino group B) number of carboxyl groups C) number of peptide bonds in the molecule D) nature of the side chain E) number of central carbon atoms 107) _ 108) The term means each enzyme catalyzes only one type of reaction A) saturation B) monoreactive C) inertia D) activation E) specificity 108) _ 109) A side chain on an amino acid is sometimes called A) a polypeptide chain B) fibrous or globular C) nucleic acid D) an R group E) an isozyme 109) _ 110) The alpha-helix and pleated sheet are examples of protein structure A) tertiary B) quaternary C) pentanary D) secondary E) primary 110) _ 111) Interaction between individual polypeptide chains to form a protein complex is structure A) quaternary B) tertiary C) pentagonal D) secondary E) primary 111) _ 112) Glycoproteins and proteoglycans are combinations of amino acids and A) lipids B) inorganic compounds C) carbohydrates D) fatty acids E) nucleic acids 112) _ 113) Which of the following is the symbol for an amino group? A) -COOH B) -OH C) -AMO 113) _ D) -NH2 E) -PO3 114) The maximum rate of an enzyme reaction occurs at A) synthesis B) saturation limit C) hydrolysis D) reversible E) dehydration 114) _ 115) How would the lack of a cofactor for an enzyme affect that enzyme's function? A) The enzyme would not be able to function B) The enzyme would function more quickly C) The enzyme's function would not be altered D) The enzyme would function more slowly E) The enzyme would cease to function after reaching a maximum rate 115) _ 116) An example of an organic substance is: A) lipid and protein B) nucleic acid C) lipid, nucleic acid, and protein D) lipid E) protein 116) _ 117) Molecules that store and process genetic information are the A) lipids B) steroids C) nucleic acids D) carbohydrates E) proteins 117) _ 118) An amino acid is to a protein as is to a nucleic acid A) a purine B) a nucleotide C) a proton D) a neutron E) a protein 118) _ 119) A nucleotide consists of A) a five-carbon sugar and a nitrogenous base B) a phosphate group and a nitrogenous base C) a five-carbon sugar, a nitrogenous base, and a phosphate group D) a five-carbon sugar and an amino acid E) a five-carbon sugar and phosphate group 119) _ 120) According to the rules of complementary base pairing in nucleic acids, cytosine would pair with the base A) uracil B) thymine C) adenine D) cytosine E) guanine 120) _ 121) Adenine and guanine are A) nucleotides represented by A and G B) purines represented by T and C C) purines represented by A and G D) pyrimidines represented by A and G E) pyrimidines represented by T and C 121) _ 122) The structure of RNA differs from DNA in that A) DNA contains pyrimidines but not purines B) RNA contains pyrimidines but not purines C) RNA contains purines but not pyrimidines D) the backbone of RNA contains ribose E) DNA contains purines but not pyrimidines 122) _ 123) The most abundant high-energy compound in cells is A) DNA B) adenosine triphosphate C) adenosine monophosphate D) RNA E) adenosine diphosphate 123) _ 124) A high-energy bond in ATP is present A) between the first and second phosphate group B) between the second and third phosphate group C) between adenine and a phosphate group D) between adenine and ribose E) between phosphate groups and and between phosphate groups and 124) _ 125) The phosphorylation of adenosine forms A) 2ATP B) ribose C) ATP 125) _ D) ADP E) AMP 126) Identify the product formed from the phosphorylation of ADP A) adenosine diphosphate B) deoxyribonucleic acid C) adenine D) adenosine triphosphate E) ribose 126) _ 127) AMP + P → A) ADP 127) _ B) DNA C) 2ADP D) ATP E) adenine 128) The average time between synthesis and breakdown is known as the time A) anabolism B) metabolism C) turnover D) specificity E) catabolism 128) _ 129) Muscle proteins are destroyed after 17 days and then replaced This is an example of A) disease B) surveillance C) specificity D) metabolic turnover E) surface tension 129) _ 130) Continuous breakdown and replacement of cellular molecules is termed A) metabolic turnover B) metabolism C) organic chemistry D) anabolic turnover E) catabolic turnover 130) _ SHORT ANSWER Write the word or phrase that best completes each statement or answers the question 131) A(n) is a pure substance composed of atoms of only one kind 131) 132) The center of an atom is called the 132) 133) Electrons whirl around the center of the atom at high speed, forming a(n) 133) 134) Electrons in an atom occupy an orderly series of electron shells or 134) 135) The actual mass of an atom is known as its 135) 136) Atoms of the same element whose nuclei contain the same number of protons, but different numbers of neutrons, are called 136) 137) The of a radioactive substance is the time required for 50 percent of a given amount of radioisotope to decay 137) 138) Ions with a positive charge are called 138) 139) Ions with a negative charge are called 139) 140) Kinetic energy is stored as energy when a spring is stretched 140) 141) Chemical reactions that release energy are called 141) 142) Chemical reactions that absorb energy are called 142) 143) The three familiar states of matter are solids, liquids, and 143) 144) Chemical reactions that occur in the body are accelerated by 144) 145) In living cells, complex metabolic reactions proceed in a series of steps called a(n) 145) 146) Compounds that contain carbon as the primary structural atom are called molecules 146) 147) Compounds that not usually contain carbon as the primary structural atom are called molecules 147) 148) A(n) is a homogeneous mixture containing a solvent and a solute 148) 149) Soluble inorganic compounds whose solutions will conduct an electric current are called 149) 150) Molecules that not readily interact with water are called 150) 151) The of a solution is the negative logarithm of the hydrogen ion concentration expressed in moles per liter 151) 152) All fatty acids contain a functional group at one end called the 152) 153) In water, phospholipids tend to form tiny droplets with hydrophobic tails buried inside called 153) 154) Molecules with two fatty acid chains and a phosphate group that form biological membranes are called 154) 155) Individual steroids differ in the attached to the carbon rings 155) 156) The molecule DNA contains a five-carbon sugar called 156) 157) The purines found in DNA are and guanine 157) 158) The pyrimidine bases found in DNA are and cytosine 158) 159) The three structural components of a nucleotide are a pentose, a phosphate group, and a _ base 159) 160) A(n) is a covalent bond that stores an unusually large amount of energy 160) 161) In the process of a phosphate group is transferred to a molecule 161) 162) The hydrolysis of ATP yields ADP, phosphate ion, and 162) ESSAY Write your answer in the space provided or on a separate sheet of paper 163) The element sulfur has an atomic number of 16 and mass number of 32 How many neutrons are in the nucleus of a sulfur atom? If sulfur forms covalent bonds with hydrogen, how many hydrogen atoms can bond to one sulfur atom? 164) What role buffer systems play in the human body? 165) Blood has a very narrow normal pH range but urine has a very broad normal pH range What does that indicate about the physiology of pH? 166) Explain the role of water molecules in polysaccharide formation 167) How does the DNA molecule control the appearance and function of a cell? 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) 25) 26) 27) 28) 29) 30) 31) 32) 33) 34) 35) 36) 37) 38) 39) 40) 41) 42) 43) 44) 45) 46) 47) 48) 49) 50) 51) C D C D A A B B C C D C E B E D C E B D C A C B E D C C D A A A B D B B D E D D C A B B A B C D A C C 52) 53) 54) 55) 56) 57) 58) 59) 60) 61) 62) 63) 64) 65) 66) 67) 68) 69) 70) 71) 72) 73) 74) 75) 76) 77) 78) 79) 80) 81) 82) 83) 84) 85) 86) 87) 88) 89) 90) 91) 92) 93) 94) 95) 96) 97) 98) 99) 100) 101) 102) 103) D B A C D A B D A B A B B A B E C E E D B C E D A E A C E A C A A E E C E A D D B D E A C C C D E A B B 104) 105) 106) 107) 108) 109) 110) 111) 112) 113) 114) 115) 116) 117) 118) 119) 120) 121) 122) 123) 124) 125) 126) 127) 128) 129) 130) 131) 132) 133) 134) 135) 136) 137) 138) 139) 140) 141) 142) 143) 144) 145) 146) 147) 148) 149) 150) 151) 152) 153) 154) 155) E E D D E D D A C D B A C C B C E C D B E E D A C D A element nucleus electron cloud energy levels atomic weight isotopes half-life cations anions potential exergonic endergonic gases enzymes pathway organic inorganic solution electrolytes hydrophobic pH carboxylic acid group micelles phospholipids side chains 156) 157) 158) 159) 160) 161) 162) 163) deoxyribose adenine thymine nitrogenous high-energy bond phosphorylation energy The number of neutrons in an atom is equal to the mass number minus the atomic number Thus, sulfur has 32 - 16 = 16 neutrons The atomic number indicates the number of protons, so a neutral sulfur atom contains 16 protons plus 16 electrons to balance the protons electrically The electrons would be distributed as follows: in the first electron shell, in the second, and the remaining in the third To achieve a full electrons in the third (outermost) electron shell, the sulfur atom can accept electrons in an ionic bond or can share electrons in a covalent bond Because hydrogen atoms can share one electron in a covalent bond, the sulfur atom can form two covalent bonds with hydrogen, one with each of two hydrogen atoms In chemical notation, this is H 2S 164) Buffer systems help maintain pH within normal limits by removing or replacing hydrogen ions as needed 165) Homeostasis requires that the pH of body fluids be maintained almost constant to avoid disruptions of healthy function To accomplish this, the urinary system eliminates or retains hydrogen ion as needed These actions cause the pH of urine to vary widely, depending on whether there is too much or not enough hydrogen ion in the body 166) Water molecules are removed in the dehydration synthesis of polysaccharides 167) The DNA molecule controls the synthesis of enzymes and structural proteins By controlling the synthesis of structural proteins, the DNA is able to influence the physical appearance of a cell By controlling the production of enzymes, the DNA is able to control all aspects of cellular metabolism and thus control the activity and biological functions of the cell