Molecular Ch 21

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

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 __________.

nitrate leaches out of soils easily due to its negative charge

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?

Hg2+

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.

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 increases, which increases the activity of the microorganism there and upsets the balance of the ecosystem. Submit

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?

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 yield N2. Need more. Model answer: Both denitrification and the anammox reaction serve to remove nitrate from the environment--converting the nitrogen to dinitrogen gas. Denitrification is much more common in the soil. In these locations, bacteria use the oxidized nitrogen as a terminal electron sink for anaerobic respiration. The anammox reaction, in contrast, occurs in anaerobic environments. It is most common in deep ocean waters where this reaction can account for up to half of the dinitrogen gas production. Excess denitrification can adversely affect crop production by depleting the available nitrogen in the soil. In addition, this process can generate intermediates associated with global warming (N2O) and acid rain (NO). The anammox reaction is most directly important to society in its role in wastewater treatment. This reaction helps us to avoid eutrophication by reducing the nitrogen levels in wastewater effluent.

Decomposition of organic carbon ultimately results in the formation of __________.

CO2 in aerobic environments and CO2 plus CH4 in anoxic environments

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 __________.

building the shells and frustules of microscopic algae and some animals

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

The calcium cycle is tightly coupled to the

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.

cytochromes

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) __________.

electron acceptor

In anoxic environments, organic compounds are cycled back to carbon dioxide and methane by __________.

fermentation

Bacteria, such as Leptothrix, must have a mechanism to manage the end products when utilizing iron for oxidation, because __________.

ferric iron is insoluble and will build up in or on the cell

Agricultural application of nitrogen fertilizer

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

The two major forms of carbon that remain following microbial degradation are

methane and carbon dioxide.

Nitrification and anammox both

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

Nitrous oxide (N2O) is a

potent greenhouse gas that is a product of denitrification.

What would the result be when a soil is supplemented with S0?

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 __________.

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 redox changes or gaseous forms that can alter Earths atmospheric chemistry.