r 3 Microbial Metabolism The prokaryotic transport system that involves a substrate-binding protein, a membrane-integrated transporter, and an ATP-hydrolyzing protein is the ABC transport system. group translocation. symport. simple transport. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.2 The sum of all biosynthetic reactions in a cell is known as metabolism. anabolism. catabolism. synthatabolism. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Based on the functional roles of phosphate in various microbial metabolisms, which of the following compounds most likely contain phosphate? organic compounds inorganic compounds both organic and inorganic compounds neither organic nor inorganic compounds Answer: C Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.1 Which of the following would be used by a chemoorganotroph for energy? C2H3O2- H2 CO2 H Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Which of the following statements is FALSE? Most bacteria are capable of using ammonia as their sole nitrogen source. Some bacteria are able to use nitrates or nitrogen gas as their nitrogen source. Most available nitrogen is in organic forms. Nitrogen is a major component of proteins and nucleic acids. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.6 All microorganisms require carbon, iron, and sodium. phosphorus, aluminum, and sodium. calcium, potassium, and magnesium. phosphorus, selenium, and sulfur. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Which element functions BOTH as an enzyme cofactor and as a stabilizer of ribosomes and nucleic acids? iron hydrogen zinc magnesium Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.1 Based on your understanding of metabolism, generalize when an enzymeʹs rate of activity can be changed. before enzyme production during enzyme production after enzyme production at any point—before, during, or after enzyme production Answer: C Bloom’s Taxonomy: 5-6: Evaluating/Creating The change in Gibbs free energy for a particular reaction is most useful in determining the amount of energy catalysts required for biosynthesis or catabolism. the potential metabolic reaction rate. whether there will be a requirement or production of energy. energy stored in each compound. Answer: C Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.4 Which is an example of a micronutrient? arginine inorganic phosphorous iron vitamin B12 Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.1 Aseptic technique refers to a series of practices to avoid contamination. the autoclave and other sterilizing procedures. cleanliness in the laboratory. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 1.9 To ensure growth of a newly discovered bacterium with unknown nutritional requirements, it would be best to begin with a medium rather than a medium. complex / minimal minimal / complex selective / complex selective / differential Answer: A Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.2 If ΔG0ʹ is negative, the reaction is endergonic and requires the input of energy. exergonic and energy will be released. endergonic and energy will be released. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.4 Activation energy is the energy required for a chemical reaction to begin. given off as the products in a chemical reaction are formed. absorbed as ΔG0ʹ moves from negative to positive. needed by an enzyme to catalyze a reaction without coenzymes. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.5 requires more reactants but makes the reaction rate faster. increases the amount of reactants produced but does not change the rate. changes the rate of the reaction but does not change the end amount of products. changes both the rate of a reaction and the amount of the product that will be obtained as the reaction is completed. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.5 16) The portion of an enzyme to which substrates bind is referred to as the substrate complex. active site. catalytic site. junction of van der Waals forces. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.5 Coenzymes are essential for an enzymeʹs function and prosthetic groups only enhance its reaction rate. Coenzymes are weakly bound whereas prosthetic groups are strongly bound to their respective enzymes. Coenzymes are organic cofactors and prosthetic groups are inorganic cofactors. Coenzymes require additional ions to bind to enzymes but prosthetic groups are able to directly interact with enzymes. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.5 If an oxidation reaction occurs simultaneous reduction of a different compound will also occur, because electrons do not generally exist alone in solution. another oxidation reaction will occur for a complete reaction, because one oxidation event is considered a half reaction. a cell is undergoing aerobic respiration, because oxygen is being used. a reduction reaction would not occur, because they are opposite reaction mechanisms. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding The class of macromolecules in microorganisms that contributes most to biomass is carbohydrates. DNA. lipids. proteins. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.1 A chemoorganotroph and a chemolithotroph in the same environment would NOT compete for oxygen. carbon. nitrogen. phosphorous. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.3 oxygen. carbon. nitrogen. carbon and oxygen. Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.3 22) The Embden-Meyerhof-Parnas pathway is another name for the citric acid cycle. glycolysis. electron transport. NADH production. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 1. 2. 4. 8. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 Which of the following is a common energy storage polymer in microorganisms? acetyl~S-CoA glycogen adenosine triphosphate H2 Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 Fermentation has a relatively low ATP yield compared to aerobic respiration because less ATP is consumed during the first stage of aerobic catabolism. oxidative phosphorylation yields a lot of ATP. substrate-level phosphorylation yields a lot of ATP. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 From the standpoint of fermentative microorganisms, the crucial product in glycolysis is ATP and regenerated NAD ; the fermentation products are waste products. ethanol or lactate; ATP is a waste product. CO2; ATP is a waste product. not relevant because glycolysis is not a major pathway. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 In aerobic respiration, the final electron acceptor is hydrogen. oxygen. water. ATP. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.10 Which of the following is NOT membrane-associated? NADH dehydrogenases flavoproteins cytochromes Cytochromes, flavoproteins, and NADH dehydrogenases all can be membrane-associated. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.10 During electron transport reactions OH- accumulates on the outside of the membrane while H accumulates on the inside. OH- accumulates on the inside of the membrane while H accumulates on the outside. both OH- and H accumulate on the inside of the membrane. both OH- and H accumulate on the outside of the membrane. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.11 The rising of bread dough is the result of biotin production. carbon dioxide produced by fermentation. oxidative phosphorylation. oxygen being released. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.8 Which intermediate compound(s) in the citric acid cycle is/are often used for biosynthetic pathways as well as carbon catabolism? only α-ketoglutarate only oxaloacetate only succinyl-CoA α-ketoglutarate, oxaloacetate, and succinyl-CoA Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.9 Microbial growth on the two-carbon acetate substrate invokes the citric acid cycle for aerobic catabolism. both the citric acid and glyoxylate pathways. the glyoxylate pathway. the glyoxylate and glycolysis pathways. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.9 Which is one major difference between anaerobic and aerobic respiration? electron donor electron acceptor use of electron transport use of proton motive force Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.12 For a carbon source, chemoorganotrophs generally use compounds such as acetate, succinate, and glucose. bicarbonate and carbon dioxide. nitrate and nitrite. acetate, bicarbonate, and nitrate. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.3 All of the following are non-protein electron carriers EXCEPT FADH2. FMNH2. cytochromes. quinones. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.10 Which two metabolic processes are most dissimilar? citric acid cycle and glycolysis glycolysis and gluconeogenesis proton motive force and substrate-level phosphorylation pentose phosphate pathway and glycolysis Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.13 How does the proton motive force lead to production of ATP? ATPase requires one proton to make one ATP. Protons must be pumped against a concentration gradient from outside of the cell into the cell to rotate the F0 subunit of ATPase for the F1 subunit to make ATP. Oxidative phosphorylation of ADP by ATP synthase requires protons as cofactors in the reaction. Translocation of three to four protons drives the F0 component of ATPase which in turn phosphorylates one ADP into ATP. Answer: D Chapter Section: 3.11 Five-carbon sugars are used in the biosynthesis of DNA and RNA. catabolic pentose phosphate pathway for carbon and energy. biosynthesis of DNA and RNA as well as catabolic pentose phosphate pathway. activation of pentoses to form glycogen for energy storage. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.13 Improperly functioning acyl carrier proteins (ACPs) would likely result in a physiological shift to anaerobic metabolism where an energized membrane is less important for energy production. enhanced growth of a bacterium due to faster growth substrate uptake by a weakened membrane. no harm to bacteria, because only archaeons and eukaryotes use ACPs for fatty acid biosynthesis. death for a bacterium due to poor lipid bilayer integrity. Answer: D Chapter Section: 3.15 A bacterium running low on NADPH could to generate more of this coenzyme. degrade an amino acid or nucleic acid invoke the pentose phosphate pathway degrade a fatty acid use a broad specificity phosphatase with inorganic phosphatase and NADH Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.13 One example of an electron acceptor that can be used in anaerobic respiration is NADH. water. nitrate. FMN. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding When culturing a chemoorganoheterophic bacterium, what outcome is LEAST likely to occur if ammonia and phosphate are provided at equal concentrations? Cells require much less P to grow than N, so extra P will be used for ATP synthesis and result in a faster growth rate. Cells will never consume all of the phosphate, because N is needed in higher quantities than P. The final biomass of cells will be no different than if only 50% of the phosphate was provided. The bacteria will import all of the ammonia to use for biosynthetic pathways. Answer: A Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.3 Most of the carbon in amino acid biosynthesis comes from citric acid cycle intermediates. citric acid cycle intermediates and glycolysis products. glycolysis products. glycolysis intermediates and products. Answer: B Chapter Section: 3.14 Which metabolic cycle or pathway is LEAST likely to be invoked during the biosynthesis of DNA? citric acid cycle glycolysis gluconeogenesis pentose phosphate pathway Answer: C Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.14 Hypothetically, if free electrons existed in sufficient numbers for enzymes to use in metabolic reactions a higher diversity of cytochromes would likely be observed. cytochromes would be unnecessary for cells and quinones would be more important. Q-cycle reactions would no longer be necessary for electron transport, but the proton motive force would otherwise be unchanged. most metabolic pathways for both anabolism and catabolism would have to be rewritten. Answer: D Chapter Section: 3.11 Which metabolic strategy does NOT invoke the proton motive force for energy conservation? aerobic catabolism fermentation chemoorganotrophy photoautrophy Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.12 True/False Questions ATP-binding cassette transport systems have high substrate affinity and thus help microorganisms survive in low nutrient environments. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding A bacterial isolate that grows better on a nutrient agar plate supplemented with amino acids but still grows in a nutrient agar plate lacking amino acids suggests amino acids are trace nutrients for the isolate. Answer: FALSE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.1 Regeneration of oxaloacetate is essential for the citric acid cycle to be cyclical. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.9 Depending on the particular metabolism of a bacterium, electron transport can be used to energize and rotate ATP synthase. Answer: FALSE Chapter Section: 3.11 Each amino acid made during protein biosynthesis first requires a separate biosynthetic pathway to be invoked by a cell. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.14 The terminating step of moving electrons onto oxygen releases additional ATP during aerobic metabolism not made during anaerobic growth. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.11 Nitrogenases not only reduce N2 but also can act on acetylene (C2H2). Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.1 Due to the number of phosphate groups, ATP has approximately three times more energy stored than AMP, and ADP has approximately two-thirds the energy stored of ATP. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.7 In a given chemical reaction, if the free energy of formation is known for all of the reactants and each of the products, the change in free energy can be calculated for the reaction. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.4 Free-energy calculations are dependent on the rates of the reactions. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.4 With respect to nitrogen utilization, relatively few bacteria can use NH3 whereas many more can make use of N2. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.14 The proton motive force is most often generated by splitting of H2. Answer: FALSE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.11 Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.13 If a substance is reduced, it gains electrons. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.6 Molybdenum is a cofactor for nitrogenase, which means every nitrogen-fixing microorganisms will not be able to fix nitrogen without Mo. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.1 Magnesium is not considered a growth factor for microorganisms, because growth factors are always organic compounds. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.1 Cells require iron supplemented in their growth medium as a trace metal, because it is consumed by quinones during electron transport for ATP production. Answer: FALSE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.10 Varied coenzyme availability increases the diversity of enzymatic reactions in both biosynthetic and catabolic pathways possible in a cell. Answer: TRUE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.5 The energy released from the hydrolysis of coenzyme A is conserved in the synthesis of ATP. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.7 In substrate-level phosphorylation, ATP storage is depleted during the steps in catabolism of the fermentable compounds. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.8 Catabolic pathways are essential for microorganisms to obtain energy, because biosynthetic reactions for cellular growth generally require energy input. Answer: TRUE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.13 In electron transport systems, the electron carriers are membrane associated. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.11 Heme prosthetic groups are involved in electron transfer with quinones. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.5 During the electron transport process, protons and electrons become physically separated in the cell membrane. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.10 Many defined growth media that support microbial growth lack malonate, which is an important precursor for biosynthesis of lipid membranes. Based on this, we can infer cells also must have a metabolic pathway to generate malonate from other compounds. Answer: TRUE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.15 The net result of electron transport is the generation of a pH gradient and an electrochemical potential across the membrane. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.11 A bacterium that lacks an arginine biosynthetic pathway would still be able to make proteins with arginine and grow only if arginine is supplemented into the growth medium. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.14 Essay Questions Why is energy required for nutrient transport? Give an example of a system that transports nutrients and describe what source of energy is used to move the nutrients into the cell. Answer: Energy is required for nutrient transport because nutrient concentration outside of the cell is lower than the nutrient concentrations inside the cell, thus nutrient transport moves solutes against a concentration gradient and requires energy. There are three examples in the text. The student could describe any one of them. They are (i) Simple transporter such as lac permease. Each nutrient molecule is cotransported into the cell with a H ion, thus the proton motive force provides the energy to transport nutrients. (ii) Group translocation such as sugar phosphotransferases. Each nutrient molecule is modified during the transport process. The modification, in this case, phosphorylation, releases energy, thus the energy source is an energy-rich compound such as phosphoenol pyruvate or some other phosphorylated compound. (iii) ABC transporters. In this example specific binding proteins bind to nutrient molecules with high affinity. Movement of the nutrient into the cell is coupled to ATP hydrolysis, thus ATP is the source of energy for transporting nutrients. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.2 Explain the differences between symporters, and antiporters. Answer: Answers should highlight differences in transport direction and energy input. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.2 Compare and contrast defined media and complex media. Use specific examples in your answer. Answer: Defined media are prepared by adding individual “pure” chemicals in known quantities. In this way, the medium itself can be explicitly defined. For example, 5 mM NaCl, 3 mM KH2PO4, 1.5 mM NH4Cl, 2.5% glucose, and 3% acetate is a defined medium, because each ingredient added is at a known concentration and the chemicals present are known. Complex media needs only to contain one undefined product to be considered complex or undefined. An example of an undefined medium is 5 mM NaCl, 2.5% tryptone and 2.5% yeast extract, because both tryptone and yeast extract are not individual chemical structures but instead contain an assortment of compounds at unknown (imprecise) quantities. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.1 Categorize the circumstances under which the same substance (molecule) can be either an electron donor or an electron acceptor. Answer: Answers should explain that not all molecules are strictly one or the other, and each molecule must be compared to the other in a pair to determine which is the electron acceptor and which is an electron donor. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.6 Contrast fermentation and respiration in terms of electron donor, electron acceptor, type of ATP production, and relative number of ATP produced. Answer: Respiration should be distinguished as using separate electron donors and acceptors (such as organic carbon as the electron donor and oxygen as the electron acceptor), while fermentation splits organic molecules in order to oxidize one part of the molecule and reduce the other part in order to regenerate NAD . Fermentation uses substrate level phosphorylation to generate relatively few ATP, while respiration uses oxidative phosphorylation to generate more ATP. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.8 Summarize the roles the proton motive force has in microbial metabolism. Answer: The proton motive force uses an energized cell membrane for ATP synthesis via ATPase, transporting some ions and molecules into and out of the cell, and flagellar rotation. Chapter Section: 3.11 Discuss why energy yield in an organism undergoing anaerobic respiration is less than that of an organism undergoing aerobic respiration. Answer: One possible explanation could point to the substrate-level phosphorylation process itself as being less energy yielding than (aerobic) oxidative phosphorylation. Another reason is the fate of pyruvate itself, where fermentation is unable to take it through the higher energy yielding process, which requires O2 as a terminal electron acceptor. Other answers could discuss the E0ʹ being greatest with the O2/H2O redox couple in aerobic metabolism compared to anaerobic redox couples. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.12 Explain the biosynthetic and bioenergetic roles of the citric acid cycle. Answer: Some of the molecules generated during the citric acid cycle, such as alpha-ketoglutarate, oxalacetate, and succinyl-CoA, can serve as precursors for the biosynthesis of critical cellular components such as amino acids, chlorophyll, and cytochromes. The bioenergetic component of the cycle should be described in the context of FADH2 and NADH electron donors storing energy potential, usable in electron transport where O2 is reduced to water. Chapter Section: 3.8 In an aquatic microbial community where a photoautotroph, chemoorganoheterotroph, and nitrogen fixing bacterium are present, predict an environmental perturbation that would cause only one to be outcompeted by the other two groups and explain how each group would respond. Answer: Answers will vary but should highlight a unique feature of one of the groups such as: photoautotrophs are sensitive to photon (light) availability, chemoorganoheterotrophs require organic molecules for carbon, and nitrogen fixing bacteria use N2 gas. Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.3 Differentiate between exergonic and endergonic in terms of free-energy calculations. Answer: A positive change in free energy (ΔG0ʹ) means the reaction needs energy input to occur (called endergonic), whereas a negative ΔG0ʹ needs no energy input and actually releases excess energy (called exergonic). Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 3.4 Explain what an enzyme must accomplish to catalyze a specific reaction. Answer: Answers will vary, but the focus of the answer should be on overcoming the required activation energy. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.5 A beer-making microbiologist noticed that no matter how long the brewing process went, 3% alcohol was the maximum produced. Hypothesize what is causing this low level of alcohol in reference to the brewer’s recipe and recommend how a higher alcohol yield could be achieved. Ethanol is toxic at high concentrations, but ignore this factor to focus on microbial metabolism. Answer: Answers will vary but one explanation is a low substrate concentration resulted in low fermentation to produce ethanol. Providing more carbohydrates such as glucose to the yeast in the recipe for the same growth period would increase fermentation activity and ethanol production. Another explanation is that there may be too much oxygen introduced during the brewing process, which would result in the complete oxidation of glucose instead of fermentation to ethanol. The brewer would need to take more precautions to exclude oxygen during brewing. Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.8 Explain why the amount of energy released in a redox reaction depends on the nature of both the electron donor and the electron acceptor. Answer: Answers should emphasize that energy does not come from specific molecules but rather from the difference in reduction potential between two molecules. For example, assigning arbitrary values and subtracting them from one another by comparing two different electron acceptors to one donor would indicate differences in energy for an electron acceptor. In a similar way, this could also be shown to mathematically explain electron donors having an equal role in determining ΔE0ʹ. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 3.6 Consider a pizza dough made by vigorously mixing to form gluten and evenly disperse the ingredients such as bakerʹs yeast (Saccharomyces cerevisiae). Predict the metabolic differences yeast would have in a thinly flattened dough and in a spherical dough ball. Answer: A flattened dough would have higher surface area and more oxygen exposure to support aerobic respiration of S. cerevisiae. The dough ball on the other hand would initially have aerobic metabolism of S. cerevisiae due to the mixing. Once oxygen is depleted from respiration the yeast would begin anaerobic fermentation, especially in the center of the dough ball while the surface of the dough ball could still support aerobic growth if not enclosed in a container. Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 3.8 Brock Biology of Microorganisms, 15e (Madigan et al.) Chapter 5 Microbial Growth and Its Control Which of the following is/are transferred to daughter cells during bacterial cell division? only genomic DNA, the blueprint for everything the cell needs individual genes and enzymes to later be brought together to form the genome only the chromosome and enzymes to immediately begin cellular metabolism chromosome, proteins, and all other cellular constituents Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.1 Bacterial growth refers to an increase in the number of cells. the occurrence of binary fission. the time required for one cell to divide into two. the occurrence of mitosis. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding The time interval required for the formation of two cells from one is called the generation time. growth time. growth rate. division rate. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.1 Turbidity measurements are commonly utilized for monitoring planktonic cultures. biofilms. conies. sessile cultures. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding The time between inoculation and the beginning of growth is usually called the lag phase. log phase. dormant phase. death phase. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.3 Optical density and viable cell concentration are LEAST proportional to each other during the lag phase. exponential growth phase. stationary phase. death phase. Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing When attempting to determine viable cell counts of a heat-sensitive bacterial isolate, which cell counting method should be avoided? spread-plate method pour-plate method live staining and direct counting with a microscope both spread- and pour-plate methods Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.7 Bacteria that are able to grow in humans and cause disease would be classified as psychrophiles. mesophiles. thermophiles. hyperthermophiles. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing An agar plate for counting colonies and maximizing statistical validity should ideally contain 1 to 100 colonies. 50 to 100 colonies. 30 to 300 colonies. 100 to 1000 colonies. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.7 Relative to enzymes in mesophilic microorganisms, which of the following is NOT characteristic of enzymes in psychrophiles? decreased alpha helix content decreased beta sheet content fewer hydrogen bonds fewer ionic bonds Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.10 The number of colonies obtained in a plate count does NOT depend on the inoculum volume. size of the colonies. type of culture medium. incubation time. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.7 Cell density in a chemostat is controlled by the concentration of the limiting nutrient. the dilution factor. the size of the initial inoculum. the concentration of the limiting nutrient, the dilution factor, and the size of the initial inoculum. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.4 What temperature is most commonly used in autoclaves to sterilize growth media and other devices prior to experimentation? A) 95°C B) 101°C C) 121°C D) 140°C Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.15 Most mesophilic organisms can grow in a temperature range of A) 0-15°C. B) 10-20°C. C) 20-45°C. D) 50-65°C. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.9 Obligate anaerobes which are sensitive to O2 would be found growing throughout a tube of thioglycolate broth. only at the very top of a tube of thioglycolate broth. only at the bottom of a tube of thioglycolate broth. approximately one-third of the way down the thioglycolate broth. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.16 A microbe growing in a refrigerator is likely psychrophilic. mesophilic. psychrotolerant or psychrophilic. hyperthermophilic. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.10 Which of these statements is/are TRUE? The most thermophilic prokaryotes are species of Archaea. Chemoorganotrophic organisms are able to grow at higher temperatures than phototrophic organisms. All of the statements are true. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 A chemical that denatures proteins is most likely to be classified as a(n) agent. antiseptic bacteriostatic bacteriocidal detergent Answer: C Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.17 The ratio of the vapor pressure of the air in equilibrium with a substance to the vapor pressure of pure water is known as vapor activity. positive water balance. osmosis. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.13 Organisms able to live in environments with high sugar concentrations are halotolerant. osmophiles. xerophiles. anaerobic fermenting bacteria. Answer: B Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.13 When water activity is low, an organism must increase its internal solute concentration. increase its external solute concentration. decrease its internal solute concentration. decrease its external solute concentration. Answer: A Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.13 A bacterium possessing will produce O2 bubbles when placed in the presence of hydrogen peroxide. catalase superoxide dismutase superoxide reductase peroxidase Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.14 A halotolerant facultative anaerobe would grow BEST in which of the following environments? oxygen depleted saline oxygenated saline oxygen depleted non-saline oxygenated non-saline Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.13 Which of the following forms of oxygen is/are generally toxic to living organisms? superoxide anion hydrogen peroxide hydroxyl radical Superoxide, hydrogen peroxide, and hydroxyl radicals are all toxic. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.14 Superoxide dismutase and catalase work together to convert superoxide into peroxide. oxygen. water water and oxygen. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.14 Which of the following methods used to enumerate cells often requires specialized staining to observe non-pigmented bacteria? spectrophotometry/turbidity spread-plating microscopy spread-plating, turbidity, and microscopy Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.6 Which term is most relevant in describing the efficacy of an antimicrobial for use in a clinical setting? effective dose sterilization coefficient lethal dosage minimum inhibitory concentration (MIC) Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.17 Which method would be LEAST effective at sterilizing a glass hockey stick to use in the spread-plate method? autoclaving gamma radiation ethanol soaking ultrahigh-temperature pasteurization Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.15 When counting colonies on an agar plate it is assumed that each colony arose from division of one or a few cells. only viable colonies are counted. the medium must be suitable for colony growth. All of these answer choices are true. Answer: A Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.5 By controlling the concentration of nutrients continuously added to a chemostat, cells can constantly be maintained at the exponential growth phase. stationary growth phase. lag growth phase. death growth phase. Answer: A Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.4 Serial dilutions are generally made when the appropriate viable count is unknown. based on powers of 10, although other serial dilution factors are possible. to reach a suitable dilution while minimizing error. All of these answer choices apply. Answer: D Chapter Section: 5.7 Which of the following statements is FALSE? In the death phase, bacterial growth may cease as a result of oxygen and nutrient depletion. The generation time of bacteria may vary from species to species. Bacteria typically divide by binary fission, producing two daughter cells. In the lag phase, cell death exceeds cell division. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.3 The optimal growth temperature of a bacterium is most closely related to the optimal temperature for transcription of DNA. DNA replication. enzyme function. mRNA attachment to ribosomes. Answer: C Chapter Section: 5.9 Why is the enzyme catalase important to the survival of bacteria? Catalase protects the cell from desiccation. Catalase breaks down toxic hydrogen peroxide. Catalase allows for growth in high salt concentrations. Catalase aids in the transport of oxygen into the cell. Answer: B Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.14 A medium containing known substances in precise amounts is known as a media. selective complex natural defined Answer: D Chapter Section: 5.5 Selective medium differs from differential medium because selective medium permits growth of more organisms than differential medium. selective medium permits growth of a particular microbial type while differential medium is used to distinguish between types of organisms. differential medium differentiates pathogens from nonpathogens while selective medium grows only pathogens. differential medium contains growth inhibitors while selective medium does not. Answer: B Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 5.5 The cell membranes of thermophiles and hyperthermophilic bacteria typically have more saturated fatty acids. more long chain fatty acids. fewer unsaturated fatty acids. All of these answer choices are true of thermophiles and hyperthermophilic bacteria. Answer: D Bloom’s Taxonomy: 1-2: Remembering/Understanding The use of chemical agents directly on exposed body surfaces to destroy or inhibit vegetative pathogens is disinfection. sterilization. antisepsis. sanitization. Answer: C Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.17 Which of the following statements is TRUE of disinfectants? They are always effective in destroying endospores. They are used on living tissue. They are used for sterilization. They are used on inanimate surfaces. Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing A agent is a chemical that inhibits bacteria from reproducing, but does NOT necessarily kill them. bacteriostatic bacteriolytic bacteriocidal xerophilic Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.17 Microbial contamination is prevented by the use of the quadrant streak method. use of aseptic technique. use of cultures containing special nutrients. spread plate method. Answer: A Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.5 A common antimicrobial chemical (or chemicals) used as both an antiseptic and a general disinfectant is iodophors. 70% alcohol. hydrogen peroxide. Each of these chemicals at appropriate concentrations can be used as antiseptics or disinfectants. Answer: D Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.17 Cultures of a bacterial species were incubated on the shelf of a refrigerator (5°C), on a lab benchtop (25°C), on the shelf of a 37°C incubator, and on the shelf of a 50°C incubator. After incubation, there was no growth at 37°C or 50°C, slight growth on the benchtop, and abundant growth at refrigeration. What term could be used for this species? halophile mesophile anaerobe psychrophile Answer: D Chapter Section: 5.9 A microbiology student in a research lab repeated an experiment described by others using the identical bacterial isolate, the same growth medium, and the same growth conditions. However, the student was unable to achieve the same O.D. at 600 nm. What is the LEAST likely cause for this discrepancy in measured turbidity? One experiment used 16 mm wide test tubes while the other used 18 mm wide test tubes. One experiment subtracted the yellow color of the growth medium away from the final turbidity reported whereas the other used colorless water. One experiment vigorously dispersed the bacterial pellicle with vortexing while the other did not. The two experiments were carried out at vastly different elevations and did not consider the influence of pressure. Answer: D Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 5.8 True/False Questions Microbial growth is generally described as an increase in cell number rather than the expansion in size of an individual microbial cell. Answer: TRUE Chapter Section: 5.1 The duration of exponential growth would increase if bacterial cells divided into three equal daughter cells rather than two. Answer: FALSE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 5.3 A selective medium is used to suppress the growth of certain bacteria in order to facilitate the growth of other bacteria. Answer: FALSE Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 5.5 The lag phase does NOT occur if an exponentially growing culture is transferred into a nutrient rich medium with the same components and growth conditions as the previous medium. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.3 The rate of exponential growth varies greatly according to bacterial species and bioavailable nutrients. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.3 A bacterium whose optimal growth temperature is 35˚C would be classified as a thermophile. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.3 A complex medium is one that has been completely made in the laboratory and the concentration of all the nutrients is known. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.5 Many fungi and bacteria grow best at pH 5 or below. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.12 In both the lag and stationary phase, there is no net increase or decrease in viable cells. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.3 The death phase applies to individual cells rather than populations. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.3 Direct microscopic counting of cells is an accurate method for estimating the number of viable cells in a sample. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.7 The optimal pH for growth of an organism refers to its intracellular environment. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.12 When viable cell concentrations are too high to count on an agar plate, it is common to use larger sized plates to increase the surface area for counting the colonies. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.7 Refrigeration controls microbial growth in food as a result of irreversible cell damage caused by low temperature. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.9 The optimum growth temperature for an organism is typically closer to its minimum temperature rather than the maximum temperature. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.9 A bacterium such as a snow alga that is able to grow in cold temperatures is called a psychrophile. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.9 Some microbes can grow in boiling water. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 Organisms living in boiling hot springs often grow rapidly and have short doubling times. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 Taq polymerase was isolated from a thermophile and is used in the polymerase chain reaction (PCR) technique because it does not become inactivated at high temperatures. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 Mesophiles typically have longer fatty acid tails and more saturated carbon-carbon bonds in their cytoplasmic tails compared with thermophiles. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Knowledge of microbial growth patterns is useful in working with the control of microbial growth. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.15 Irreversible cell damage is more likely to occur at low rather than high temperatures. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.9 Based on studies with obligate acidophiles, high concentrations of hydrogen ions are required for their membrane stability. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing A bacterial cell in nutrient broth with a generation time of 15 minutes will produce 16 cells in 2 hours. Answer: FALSE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.2 Planktonic cells remain in suspension while sessile cells adhere to a surface. Answer: TRUE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.1 The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature. Answer: TRUE Chapter Section: 5.15 Autoclaving and pasteurization are two processes that are both very effective for sterilization. Answer: FALSE Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.15 Most microorganisms are particularly susceptible to antimicrobial agents during the logarithmic growth phase. Answer: TRUE Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.17 Sterility of a laminar flow hood is accomplished by filter-sterilized air passed through the hood quickly enough that non-sterile air does not flow into the work area. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.16 Essay Questions 1) Use the formulas N N02n and g t/n. N final cell number, N0 initial cell number, n number of generations, t time, g generation time. Find the generation time if N 2 × 108, N0 3 × 106 and t 3 hours. Answer: The number of generations (n) must first be determined through the rearranged formula: n [(log N)-(log N0)]/(log 2) to determine n 6.059 generations. Finally, the generation time (g) t/n, which equates to nearly 0.5 hours per generation or almost 30 minutes per generation. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.2 Answer: Generation time (g) and division rate (v) are reciprocal values of each other; both are determined by monitoring exponential growth over time. Division rate is reported as the number of generations per time and is calculated by taking 1/g. The units for g are in time per generation, which is the doubling time during exponential growth. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.2 Knowing the concentration of microorganisms in a sample is often an important consideration for environmental, industrial, and medical microbiologists, yet a microscope is sometimes not used to accomplish this task. Explain five major limitations to using a light microscope to directly count microorganisms. Answer: All of the following eight are potential issues associated with the direct counting method: 1) live and dead cells are indistinguishable without special staining, 2) low cell concentrations are challenging to enumerate, 3) motile cells must be immobilized, 4) precision can be quite poor with manually counting hundreds or thousands of cells, 5) small cells are difficult to observe and count even at 1,000X total magnification, 6) small particulates can be mistaken for microbial cells, 7) unstained cells require more sophisticated microscopy, and 8) it is very time-consuming. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.6 Compare and contrast the spread plate method and the pour plate method of doing plate counts. Also describe which group of organisms would not be quantifiable in the pour plate method but would still be observed in the spread plate method. Answer: Answers will vary, but one benefit to the pour plate method is that larger volumes of cells can be dispensed, whereas large liquid volumes dispensed on the surface of agar plates is often impractical. Many cells, especially psychrophiles and some mesophiles, cannot withstand the warm temperature of molten agar (~50°C) and therefore must be spread on top of an agar plate. Colonies are easier to enumerate on a two- rather than three-dimensional surface that favors the spread plate technique over the pour plate method. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.7 Enumerating the viable and total cell concentration of a population of a microbial isolate can be a laborious task for a microbiologist, especially when studying the same isolate for several years. It is often more practical to determine the relationship between optical density (OD) and cell concentration. Once this relationship (determined by a standard curve) is determined, the OD of an isolate in a broth can be used to determine the populationʹs concentration. Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve. Answer: Answers will vary, but it should be noted that a particular OD value will correspond to a specific cell concentration due to different shapes and sizes of microorganisms. One such example could be a culture of Citricella sp. SE45 which was determined to have an OD540 of 0.485. This OD fit into the already-constructed standard curve to indicate that 5 × 105 viable cells are in each milliliter of broth, which can be helpful in experiments where the final cell concentration or number is critical. To initially create the standard curve, a traditional growth curve experiment could be performed over time where both OD and cell concentration (viable with viability plating or total with direct counts) would be measured. The values of OD and cell concentration for each time point would then be used to create a standard curve, and a linear regression curve would show the relationship of OD to cell concentration such that subsequent experiments OD could be measured as a proxy for cell concentration. Bloom’s Taxonomy: 5-6: Evaluating/Creating Chapter Section: 5.8 Explain why a hyperthermophile is unlikely to be a human pathogen. Answer: The human bodyʹs temperature is approximately 37°C, which is not a favorable environment for a hyperthermophile, which has an optimal growth temperature of 80°C or higher. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 Explain the present understanding of molecular adaptations to the cytoplasmic membrane as found in psychrophiles. Answer: Non-psychrophiles do not thrive in the cold environment, in part due to predominantly having large or saturated fatty acid chains in their cytoplasmic membrane, which become increasingly rigid and wax-like with colder temperatures. The psychrophiles have higher relative concentrations of short and unsaturated fatty acids in their membrane and therefore maintain a semi-permeable membrane when exposed to less heat. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.10 Explain the present understanding of molecular adaptations to the cytoplasmic membrane that are present in thermophiles. Answer: In thermophiles and most hyperthermophilic Bacteria, the cytoplasmic membrane has a higher content of long-chain and saturated fatty acids and a lower content of unsaturated fatty acids than are found in the cytoplasmic membranes of mesophiles. Saturated fatty acids form a stronger hydrophobic environment than do unsaturated fatty acids, and longer-chain fatty acids have a higher melting point than shorter-chain fatty acids; collectively these properties increase membrane stability. Bloom’s Taxonomy: 1-2: Remembering/Understanding Chapter Section: 5.11 Would you expect a xerophilic organism to be halotolerant? Why or why not? Answer: Yes, xerophiles are typically halotolerant. For example, the xerophilic halotolerant fungus Xeromyces bisporus inhabits cereal, candy, and dried fruit, all of which are very dry environments that also contain salt. With all else being equal, a decrease in solvent (such as water) translates to an increase in solute (salt) concentration, and therefore a microbe capable of tolerating a low water activity likely can also tolerate higher salt concentrations. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.13 Describe the autoclave, and explain the roles of time, temperature, and pressure in the functioning of the autoclave. Answer: High pressure is used in an autoclave so that liquids do not boil at temperatures beyond 100°C. The heat (not pressure) is used to kill living cells and is usually used for 15 minutes at 121°C. The time must be increased for bulky samples to ensure the objects or liquids are heated to 121°C for at least 15 minutes. Bloom’s Taxonomy: 1-2: Remembering/Understanding Discuss the pros and cons of using radiation to sterilize items such as foods, drugs, and surgical supplies. Answer: UV radiation sterilizes only the surfaces of objects which can be problematic for foods that are not fully cooked on the inside. Ionizing radiation can penetrate so they are ideal for foods such as grain cereals and ground beef. The high costs associated with the specialized equipment make it feasible only for large industrial applications. Due to the high energy of some of these radiation procedures, there are many concerns of potential radioactive contamination, production of carcinogenic or toxic products, and nutritional value alteration. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.16 Why is 100% ethanol less effective as an antimicrobial compared to a 70-95% concentration of ethanol? Answer: 70% percent alcohol is ideal as opposed to a stronger solution. Pure alcohol coagulates protein on contact. If 100% alcohol is poured over a single-celled organism, the alcohol goes through the cell wall of the organism in all direction and coagulates the proteins found in the cell membrane. The coagulated membrane proteins would then stop the alcohol from penetrating further into the cell, preventing denaturation of cytoplasmic proteins. If this happened, the cell would become inactive but not dead. Under favorable conditions, the cell would then begin to function. If 70 percent alcohol is poured over a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it is able to penetrate all the way through the cell before protein coagulation can block it. Thus, the protein found in the entire cell is coagulated and the organism dies. Chapter Section: 5.17 Why are microbial doubling times in nature typically longer than those obtained in the laboratory? Answer: The general theme should be on how lab conditions are designed to optimally grow a microorganism (e.g., pH, substrate(s), temperature, vitamins) and minimize pressure. In the environment this microbe often is in conditions that are less than ideal, where they likely will encounter competition for growth substrates and other essential chemicals. Bloom’s Taxonomy: 3-4: Applying/Analyzing Chapter Section: 5.2