Microbiology Ch. 21-22 HW

Which of the following nitrogen cycle processes returns N2 to the atmosphere? Choose one or more: A. anammox reaction B. denitrification C. nitrification D. nitrogen fixation

denitrification & anammox reaction -Both denitrification and the anammox reaction return N2 to the atmosphere. Denitrifying bacteria reduces NO2- and NO3- back to N2 in anoxic environments. The anammox reaction, NH4+ + NO2- → N2 + 2 H2O, is a type of anaerobic lithotrophy and accounts for the majority of N2 that is returned to the atmosphere.

There is a hypoxic dead zone in the Gulf of Mexico due to nitrogen-rich runoff from the Mississippi River. When the Mississippi flows into the Gulf of Mexico, it introduces high levels of organic pollutants and nitrates from fertilizers. The presence of these excess nitrogen-rich substances in the Gulf of Mexico leads to a sequence of events that results in the hypoxic dead zone. Put these events, which are listed below, in sequential order.

Dead Zone Events 1. the nitrogen limitations on algal growth are lifted 2. massive algal blooms occur 3. the algae population crashes 4. dead algal cells are decomposed by microbes 5. there is an increase in the biochemical oxygen demand, resulting in reduction in oxygen the excess nitrogen introduced into the Gulf of Mexico first lifts the nitrogen limitation on algal growth, resulting in a massive algal bloom. The algae then die off and the algal population crashes. The dead algal cells are then decomposed through microbial respiration. The increased microbial oxygen consumption leads to an increased biochemical oxygen demand, depleting the water of oxygen and resulting in the hypoxic dead zone. Fish, shellfish, and crustaceans cannot survive in the dead zone.

What happens during primary wastewater treatment? Choose one: A. Microbes are added to oxidize organic compounds to carbon dioxide. B. The wastewater is pumped into drinking water reservoirs. C. Insoluble particles are removed by settling. D. The wastewater is chlorinated to eliminate pathogens.

Insoluble particles are removed by settling. In primary treatment, insoluble particles are removed by settling. Microbes are added to oxidize organic compounds to carbon dioxide during secondary treatment. In tertiary treatment, wastewater is chlorinated to eliminate pathogens.

Suppose various legume plant parts are rubbed with a protein gel. Which plant part is most likely to test positive for nitrogenase? Choose one: A. Leaves B. Flowers C. Roots D. Stems

Roots Nitrogenase is produced by bacterial endosymbionts in roots.

The steps used in a typical wastewater treatment plant are listed below. Put them in order from first to last.

Wastewater Treatment 1. removal of solid debris through screens 2. removal of insoluble particles through screen and sedimentation 3. removal of organic content, nitrogen, and phosphorus by microbes 4. filtration of particulates from microbial biofilm flocs 5. elimination of pathogens by chlorination screens are used initially to remove solid debris and particulates. Then microbes remove organic compounds and create flocs, which are then filtered to remove particulates. Finally, pathogens are eliminated, frequently with the use of chlorine.

The biochemical oxygen demand (BOD) is Choose one: A. a measure of respiration in an environmental sample. B. usually decreased by an increase in organic compounds. C. usually increased by a decrease in phosphate concentrations. D. high when microorganisms are absent in the environment.

a measure of respiration in an environmental sample. The biochemical oxygen demand (BOD) measures the rate of metabolism, and therefore oxygen consumption, in a sample. Under high BOD conditions, a water sample may quickly become anoxic. This, in turn, can adversely affect other organisms such as fish.

Nitrate incorporation into biomass is called Choose one: A. assimilatory nitrate reduction. B. dissimilatory nitrate reduction. C. nitrogen fixation. D. ammonification.

assimilatory nitrate reduction. Assimilatory indicates that the nitrate is incorporated (assimilated) into biomass. Ammonification is the conversion of organic nitrogen to ammonia. Dissimilatory nitrate reduction, or denitrification, leads to the production of N2. Nitrogen fixation is the reduction of diatomic nitrogen into ammonia.

Which of the following nitrogen cycle processes produces the greenhouse gas N2O? Choose one: A. nitrification B. anammox reaction C. nitrogen fixation D. denitrification

denitrification denitrification produces the greenhouse gas N2O through the reaction 2 NO3- → 2 NO2- → 2 NO → N2O → N2. Excess nitrates from fertilizers increase the rate of denitrification and the amount of N2O released into the atmosphere. N2O generates 200 times the warming effect of CO2.

Which of the following nitrogen cycle processes is occurring in the water sample as illustrated by the graph? Choose one: A. denitrification B. anammox reaction C. nitrogen fixation D. nitrification

denitrification the graph shows that NO3- is converted to NO2- and then to N2O in hypoxic conditions. This conversion occurs through denitrification, which reduces NO3- to NO2- and N2O. In anaerobic conditions, the NO3- and NO2- serve as electron acceptors for anaerobic respirers producing N2O and N2. The N2 production is not shown in the graph, however.

Flocs are particulates formed from microbial biofilms in wastewater treatment plants. The formation of flocs is important because it allows for the microbes to be sedimented and filtered from the water. Which of the following microbes plays an important role in floc formation? Choose one: A. filamentous microbes like Nocardia B. cyanobacteria C. swimming ciliates D. planktonic bacteria

filamentous microbes like Nocardia Nocardia is a bacterial species that forms branching filaments, which hold the floc particles together. In water treatment, it is important that the floc size be large enough to be sedimented out of the water, but not so large as to trap air and float. The ratio of filamentous microbes to single-celled microbes is important in forming floc of the correct size.

The hydrologic and carbon cycles interact. Organic carbon-containing compounds in water act as fuel for __________ by aquatic organisms. This process uses __________ and if the process occurs at too great a rate, __________ dead zones occur in the body of water. Choose one: A. photosynthesis, carbon dioxide, oxygenated B. respiration, oxygen, hypoxic C. respiration, carbon dioxide, oxygenated D. photosynthesis, oxygen, hypoxic

respiration, oxygen, hypoxic organic compounds in water are catabolized by heterotrophs through respiration. Respiration requires oxygen in the water and if it occurs too rapidly, the oxygen is depleted and hypoxic dead zones develop. The dead zone in the Gulf of Mexico is an example of what can occur when excess organic compounds are introduced into a body of water. The increase in organic compounds led to increased microbial respiration, which consumed oxygen and killed off marine life in a region the size of New Jersey.

The primary source and sink of nitrogen is Choose one: A. soil. B. forests. C. the ocean. D. the atmosphere.

the atmosphere. The primary source and sink for nitrogen is the atmosphere, where it makes up 79% of all gasses.

Label the following steps during the initiation of a root nodule symbiosis by Rhizobium:

-Rhizobium responds to plant flavonoids -Rhizobium binds to and induces root hair curling -An infection thread develops -Rhizobium travels to cortical cells -Rhizobium differentiates into bacterioids

Place the events in the correct order that leads to ocean dead zones.

1. Pollutants drain from land into ocean 2. Algae bloom in the warmth of spring 3. Algal blooms die in the winter and sink to the bottom of ocean 4. Aerobic heterotrophic bacteria on ocean bottom consume the decaying algae 5. Consumption of oxygen causes local hypoxia 6. Hypoxia kills large animals, especially those that cannot swim away

What process is occurring in this reaction? NH4+ + NO2− → N2 + 2 H2O Choose one: A. Nitrification B. Nitrogen fixation C. Anammox D. Ammonification

Anammox The anaerobic ammonium oxidation by nitrite to form diatomic nitrogen is known as anammox.

Which of the following statements is true about the relationship between the concentration of organic compounds in a body of water and its biochemical oxygen demand (BOD)? Choose one: A. As the concentration of organic compounds increases, so does the BOD. B. As the concentration of organic compounds increases, the BOD decreases. C. The concentration of organic compounds does not affect the BOD. D. As the concentration of organic compounds decreases, the BOD increases.

As the concentration of organic compounds increases, so does the BOD. the higher the concentration of organic compounds in a body of water, the higher the BOD. An increase in the amount of organic compounds in a body of water due to sewage, fertilizer runoff, or other sources will provide additional substrates for microbial respiration, thus requiring oxygen. This will increase the BOD of the body of water due to the increased microbial oxygen consumption. This increase in microbial respiration competes with the respiration of the aquatic animals, sometimes causing fish to die off.

Which of the following processes reduces the amount of nitrogen available for assimilation by plants? Choose one: A. N2 fixation to ammonium (NH4+) B. Nitrification of ammonia to nitrite (NO2-) and nitrate (NO3-) C. Oxidation of ammonia to nitrous oxide (N2O) D. Denitrification of NO2- and NO3- back to N2

Denitrification of NO2- and NO3- back to N2 Plants can assimilate ammonia, nitrite, and nitrate but cannot assimilate N2 into biomass.

In a hypothetical body of water, there are no heterotrophic microbes present. Organic pollutants enter the body of water. Will the biochemical oxygen demand (BOD) increase? Choose one: A. No, because organic pollutants do not cause a rise in BOD even in normal situations. B. No, because there are no heterotrophic microbes present to catabolize the organic compounds. C. Yes, because the BOD does not depend on the type of microbes present. D. Yes, because photosynthetic microbes will fill the niches usually occupied by the heterotrophs.

No, because there are no heterotrophic microbes present to catabolize the organic compounds. the BOD of a body of water containing no heterotrophic bacteria will not increase because the oxygen in the water will not be depleted through heterotrophic respiration.

Rank the following nitrogen compounds from the least oxidized to the most oxidized.

Oxidation State of Nitrogen Least oxidized -> Most oxidized 1. NH3 2. N2 3. NO2- 4. NO3- The correct order of the nitrogen compounds from least oxidized to most oxidized is: NH3, N2, NO2-, NO3- Nitrogen-fixing microbes reduce N2 to produce NH3, which can then be oxidized to NO2- and NO3-.

Besides organic pollutants, dead zones are also affected by nitrogen compounds. Denitrifying bacteria in the anoxic dead zones can use nitrates and nitrites as electron acceptors, thereby generating nitrous oxide, a potent greenhouse gas. What is the term used for this process? Choose one: A. nitrification B. nitrogen fixation C. dissimilatory nitrogen reduction D. assimilatory nitrogen reduction

dissimilatory nitrogen reduction Besides organic pollutants, dead zones are also affected by nitrogen compounds. Denitrifying bacteria in the anoxic dead zones can use nitrates and nitrites as electron acceptors, thereby generating nitrous oxide, a potent greenhouse gas. What is the term used for this process?

The "nitrogen triangle," illustrated in the figure below, describes the cycle of conversions between the oxidation states of nitrogen in microbial metabolism. Place the steps of the "nitrogen triangle" in the appropriate areas of the figure.

nitrogen fixation fixes N2 into NH3. Only certain bacteria and archaea fix nitrogen. The NH3 that is created is protonated into NH4+, which can be assimilated into biomass. All other organisms depend on these nitrogen fixers to provide accessible forms of nitrogen. Nitrogen fixation forms the left side of the "nitrogen triangle." Aerobic nitrification is conducted by certain bacterial species as a form of lithotrophy. The nitrifying bacteria oxidize NH3 to NO2- and NO3-. Aerobic nitrification forms the base of the triangle. In anoxic environments, anaerobic denitrification reduces NO2- and NO3- back to N2. Anaerobic respirers use the oxidized forms as alternate electron acceptors in the absence of oxygen. Anaerobic denitrification forms the right side of the triangle.

Cellular nitrogen fixation Choose one: A. requires a lot of energy. B. occurs in the absence of an enzyme. C. can occur in both prokaryotes and eukaryotes. D. leads to the oxidation of nitrogen.

requires a lot of energy. It takes a lot of energy to break the triple bond in N2. Nitrogen fixation leads to the reduction of nitrogen. The enzyme nitrogenase, found in only certain species of prokaryotes, catalyzes nitrogen fixation.

Which of the following is the most direct cause of a rise in biochemical oxygen demand (BOD) in bodies of water? Choose one: A. methanogenesis by methanogens B. chemosynthesis by lithotrophs C. photosynthesis by cyanobacteria D. respiration by heterotrophs

respiration by heterotrophs respiration of organic compounds by heterotrophs uses oxygen and increases the BOD. The health of a body of water can be monitored by measuring its BOD. This is done by measuring the oxygen uptake in a water sample by a standard set of heterotrophic bacteria.

In a wastewater treatment plant, microbes are used primarily during __________ treatment. Choose one: A. tertiary B. primary C. quaternary D. secondary

secondary In primary treatment, the sewage is clarified by settling. In secondary treatment, microbes metabolize organic wastes to carbon dioxide. In tertiary treatment, chemicals such as chlorine are added to kill microbial pathogens.