Micro chpt. 21 homework

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+

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? a. Fossile fuels (0.006%) b. Oceans and terrestrial biosphere (0.053%) c. Rocks and sediments (99.5%) d. Methane hydrates (0.014%)

Methane hydrates (0.014%)

What is favored in anoxic environments

Methanogenesis, iron reduction, sulfate-reduction

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

The aerobic process that uses ammonium (NH4+) as an energy source is referred to as ______

Nitrification

What is favored in oxic envrionments?

Nitrification, sulfide oxidation

Rates of NH3 oxidation in nature are probably controlled by archaeal _______

Nitrifiers

An assimilatory process in which N2 is converted to ammonia (NH3) for incorporation into organic nitrogen-containing molecules is __________

Nitrogen fixation

New organic compounds are produced from inorganic substrates by _____ (such as plants) and ________

Photolithotrophs, chemolithotrophs

The mer operon that is found in some bacteria is under __________.

Positive and negative control

As nutrients cycle in the biosphere, __________ can participate in every transformation from one chemical form of a nutrient to another.

Prokaryotes

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.

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

A major reservoir for calcium is __________.

The ocean

Many organisms release ammonium (NH4+) from degradation of nitrogen-containing organic materials. This process is referred to as_______

Ammonification

A process that results in anaerobic ammonia (NH3) oxidation, uses nitrite (NO2-) as the electron acceptor, and produces N2 as the product is the ______ reaction

Anammox

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

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

CO2 in aerobic environments and CO2 plus CH4 in anoxic environments

The microbes that decompose permafrost carbon to release CH4 and CO2 are most specifically examples of _____

Chemoorganotrophs

The use of nitrate (NO3-) as an electron acceptor with formation of multiple gaseous end products (N2, N2O, or NO) is ______

Denitrification

Denitrification contributes to global warming by ______

Destroying ozone

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

Sulfate reduction (SO42- → H2S) occurs only where organic material is abundant because __________.

Electrons from organic compounds are necessary for this reaction

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

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

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 general term for organisms that have to use preformed organic molecules is _____ whereas the general term for those that can use CO2 to synthesize organic molecules are ____

heterotrophs, autotrophs

Human influences on the carbon cycle may cause major upsets in the balance of the ecosystem because __________.

increasing the anthropogenic carbon dioxide released in the atmosphere may significantly decrease the amount of calcium carbonate in the deep ocean

H2S that these newly described organisms use is at the highest concentration in anoxic marine habitats because ______ produce it as an end product of anaerobic respiration, oxidizing H2 or small organic compounds with sulfate as the terminal electron acceptor.

sulfate-reducing bacteria

Phosphorus is cycled like carbon, nitrogen, and sulfur, except for the fact that __________.

there are no gaseous forms that can alter the chemistry in the atmosphere

A farmer wants to acidify his alkaline soils by adding elemental sulfur (S0), which will, under the right conditions, be oxidized to H2SO4 by chemolithotrophs. However, the weather report predicts heavy rains and possible localized flooding starting within in a few days and lasting for the next couple of weeks. Why should the farmer wait to apply the S0 to his fields until the soils are well-drained?

to avoid production of hydrogen sulfide (H2S) due to anoxia