Chapter 21 Homework Questions

Lignin is a complex polymer of methoxylated ________ compounds and is present in ________. oil / fossil fuels mineral / rocks silica / aquatic environments aromatic / vascular plant material

aromatic / vascular plant material

Geobacter sulfurreducens uses its pili to form direct connections with insoluble ferric iron particles. As the organism carries out respiration, the Fe3+ is acting as a(n) __________. micronutrient electron donor electron acceptor carbon source

electron acceptor

Methanogens, among other compounds, use alcohols and fatty acids to synthesize methane gas in anoxic environments. True False

False

Some microbial transformations of mercury yield more toxic forms of mercury, including the most toxic form, methylmercury (CH3Hg+). Which of the following properties of methylmercury in an aquatic ecosystem would be most problematic for humans? Methylmercury is a neurotoxin. Methylmercury absorbs readily through the skin. Methylmercury accumulates in animal muscle and is biomagnified in the food chain. Methylmercury is water-soluble.

Methylmercury accumulates in animal muscle and is biomagnified in the food chain.

What is the major reservoir of stable nitrogen? NO3- NO NH4 N2

N2

Why would using nitrogenous fertilizer near a body of water affect the organisms in the body of water? When runoff enters the body of water, the nitrogen level significantly decreases, which increases the activity of the microorganisms there and upsets the balance of the ecosystem. It would not affect the organisms in the water, only those in the soil where the fertilizer is applied. When runoff enters the body of water, the nitrogen level significantly increases, which decreases the activity of the microorganisms there and upsets the balance of the ecosystem. When runoff enters the body of water, the nitrogen level significantly increases, which increases the activity of the microorganism there and upsets the balance of the ecosystem

When runoff enters the body of water, the nitrogen level significantly increases, which increases the activity of the microorganism there and upsets the balance of the ecosystem

The two major forms of carbon that remain following microbial degradation are methane, organic matter, and fossil fuels. lignin and fossil fuels. methane and carbon dioxide. organic matter and hydrocarbons.

methane and carbon dioxide.

Carbon dioxide and methane are potent greenhouse gases, with methane having 20 times more warming potential in the atmosphere than CO2. As global warming progresses, there is the real possibility that increased temperatures on land and in the oceans will lead to a positive feedback effect leading to accelerated warming. From the carbon reservoirs listed below with their percentage of the total carbon on Earth, what would be the most dangerous potential source of C that could be released to potentiate further warming? oceans and terrestrial biosphere (0.053%) rocks and sediments (99.5%) methane hydrates (0.014%) fossil fuels (0.006%)

methane hydrates (0.014%)

Compare and contrast denitrification and the anammox reaction. Where in the environment are these reactions most important? Why are these reactions important to society?

Both denitrification and the anammox reaction serve to remove nitrate from the environment--converting the nitrogen to dinitrogen gas. Denitrification:NO3- reduction to N2, NO, or N2O Denitrification is the main way N2 and N2O are formed biologically. By converting NO3- in wastewater to volatile forms of Nitrogen, denitrification minimizes fixed Nitrogen in discharge waters and subsequent algal growth triggered by the nintrate influx. Denitrification can lead to deficiencies in some habitats. Anammox: a process where ammonia is oxidized under anoxic conditions Anammox is a major process in sewage and in anoxic marine basins and sediments. It isn't a significant process in oxic soils.

Which is the most toxic form of mercury? Hg0 Hg4+ CH3Hg+ Hg2+

CH3Hg+

Decomposition of organic carbon ultimately results in the formation of __________. CO2 in aerobic environments and CO2 plus CH4 in anoxic environments CH4 in aerobic environments and CO2 in anoxic environments CO2 in aerobic environments and CH4 in anoxic environments CO2 plus CH4 in aerobic environments and CH4 in anoxic environments

CO2 in aerobic environments and CO2 plus CH4 in anoxic environments

Abiotic oxidation of Fe2+ requires oxygen and occurs rapidly when the pH is near 7. True False

True

Some mercury-resistant bacteria can convert toxic forms of mercury to less toxic forms using the mer operon under transcriptional regulation the merR protein. What molecule would you predict binds to merR to cause it to act as a repressor or as an activator of transcription for this operon? MerP periplasmic binding protein Hg2+ H0 NADH

Hg2+

What reaction is catalyzed by mercuric reductase? CH3Hg+ to Hg2+ CH3HgCH3 to Hg2+ Hg2+ to Hg0 Hg4+ to Hg2+

Hg2+ to Hg0

The ocean has mitigated the impact of anthropogenic carbon dioxide production by absorbing 500 billion tons of atmospheric carbon dioxide and over 80% of the trapped heat energy. absorbing over 80% of the trapped heat energy. storing 600 billion tons of organic carbon. absorbing 500 billion tons of atmospheric carbon dioxide.

absorbing 500 billion tons of atmospheric carbon dioxide and over 80% of the trapped heat energy.

Increases in atmospheric carbon dioxide concentrations leads to acidification of the oceans as CO2 dissolves in the water and forms carbonic acid. This acidification is predicted to have a major effect on the carbon cycle, as well as the calcium and silica cycles, due to the roles of Ca+ and Si in __________. the formation of carbonate rocks the formation of fossil fuels mercury oxidation building the shells and frustules of microscopic algae and some animals

building the shells and frustules of microscopic algae and some animals

The calcium cycle is tightly coupled to the carbon cycle through calcium carbonate formation in ocean waters. nitrogen cycle because nitrogenase requires calcium ions. phosphorus cycle through calcium phosphate formation in sediments and rocks. silica cycle through calcium silicate formation in coastal ocean sediments.

carbon cycle through calcium carbonate formation in ocean waters.

Sulfide is toxic to respiring organisms, because it can combine with metals present in ________ that serve a critical function in respiration. oxidases cytochromes glycolysis enzymes NADH

cytochromes

Lysis of marine algae and cyanobacteria releases the major osmoregulatory solute, dimethylsulfoniopropionate (DMSP), which is degraded into the most abundant organic S compound in nature, ________. elemental sulfur (So) hydrogen sulfide (H2S) gypsum (CaSO4) dimethyl sulfide (CH3-S-CH3)

dimethyl sulfide (CH3-S-CH3)

In anoxic environments, organic compounds are cycled back to carbon dioxide and methane by __________. fermentation cellular respiration glycolysis metabolism

fermentation

Agricultural application of nitrogen fertilizer increases global warming by increasing microbial respiration in agricultural soils. reduces global warming by increasing the storage of carbon dioxide in plant biomass. increases global warming by increasing the production of nitrous oxide (N2O) by denitrification in agricultural soils. has little to no effect on the carbon cycle.

increases global warming by increasing the production of nitrous oxide (N2O) by denitrification in agricultural soils.

Both ammonium (NH4+) and nitrate (NO3-) are assimilated by primary producers, but ammonium is the preferred form of nitrogen for fertilizers used in agriculture because __________. ammonium leaches out of soils easily due to its positive charge ammonium is converted to nitrate by microbial nitrification ammonium does not cause eutrophication (algal blooms) if it enters aquatic ecosystems nitrate leaches out of soils easily due to its negative charge

nitrate leaches out of soils easily due to its negative charge

Many nutrient cycles are coupled and changes in one cycle will affect another. This means that a change in the amount of carbon dioxide fixed is intimately affected by the amount of __________. nitrogen available in an ecosystem oxygen available in an ecosystem methane available in an ecosystem hydrogen available in an ecosystem

nitrogen available in an ecosystem

Nitrification and anammox both are aerobic processes, but nitrification produces NO3- and annamox produces N2 gas. create nitrogen gas, but nitrification is aerobic while anammox is anaerobic. occur in soils at neutral pH. oxidize ammonia, but nitrification uses O2 as an electron acceptor and anammox uses NO2-.

oxidize ammonia, but nitrification uses O2 as an electron acceptor and anammox uses NO2-.

Nitrous oxide (N2O) is a direct product of ammonification. potent greenhouse gas that is a product of nitrification. direct product ofnitrogen fixation. potent greenhouse gas that is a product of denitrification.

potent greenhouse gas that is a product of denitrification.

What would the result be when a soil is supplemented with S0? dimethyl sulfide production due to mixotrophs soil acidification due to chemolithotrophs syntrophic utilization of sulfite organic carbon production due to anaerobes

soil acidification due to chemolithotrophs

Industrial production of nitrogenous fertilizers from N2 now equals or exceeds the amount of nitrogen fixation carried out by microbes in the biosphere. The resulting increase in primary production is an example of the fact that __________. synthetic fertilizers work better than natural N sources for primary production N is generally not a limiting nutrient for primary production there is a fixed quantity of N on Earth the C and N cycles are closely coupled

the C and N cycles are closely coupled

One important difference between the C, N, and S cycles and the P, Ca, and Si cycles is that the P, Ca, and Si cycles do NOT involve microbial activity. the P, Ca, and Si cycles do NOT involve redox changes or gaseous forms that can alter Earths atmospheric chemistry. P, Ca, and Si are NOT cycled in terrestrial environments. the P, Ca, and Si cycles are NOT affected by global warming or other human activity.

the P, Ca, and Si cycles do NOT involve redox changes or gaseous forms that can alter Earths atmospheric chemistry.