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Questions and Answers
What are the major carbon reservoirs on Earth?
What are the major carbon reservoirs on Earth?
- Atmosphere, land, oceans, freshwater, sediments, rocks, and biomass (correct)
- Atmosphere, water bodies, soil, and living organisms
- Atmosphere, crust, rivers, and forests
- Atmosphere, lithosphere, hydrosphere, and biosphere
What is the largest source of CO2 release to the atmosphere?
What is the largest source of CO2 release to the atmosphere?
- Human activities
- Microbial decomposition (correct)
- Industrial processes
- Volcanic eruptions
What has led to steadily increasing temperatures worldwide?
What has led to steadily increasing temperatures worldwide?
- Changes in ocean currents
- Rise in atmospheric carbon dioxide (correct)
- Increase in methane production
- Decrease in atmospheric oxygen
What are the end products of decomposition?
What are the end products of decomposition?
Which process reduces inorganic carbon dioxide to organic carbohydrates?
Which process reduces inorganic carbon dioxide to organic carbohydrates?
What dominates aquatic environments in reducing the level of carbon dioxide in the atmosphere?
What dominates aquatic environments in reducing the level of carbon dioxide in the atmosphere?
What is the main product of microbial conversion of methane?
What is the main product of microbial conversion of methane?
What are methane hydrates formed from?
What are methane hydrates formed from?
What is the process that involves the oxidation of ammonia to nitrate?
What is the process that involves the oxidation of ammonia to nitrate?
In which environments does acetogenesis occur, competing with methanogenesis?
In which environments does acetogenesis occur, competing with methanogenesis?
What is the primary process involved in carbon cycling in anoxic environments?
What is the primary process involved in carbon cycling in anoxic environments?
What is the main process involved in the reduction of carbon dioxide to methane?
What is the main process involved in the reduction of carbon dioxide to methane?
Which process involves the reduction of nitrate to nitrogen gas?
Which process involves the reduction of nitrate to nitrogen gas?
What is the primary process involved in the oxidation of ammonia to nitrite?
What is the primary process involved in the oxidation of ammonia to nitrite?
Where is methanogenesis commonly observed?
Where is methanogenesis commonly observed?
What process is beneficial in wastewater treatment by removing fixed nitrogen?
What process is beneficial in wastewater treatment by removing fixed nitrogen?
Which process involves the reduction of carbon dioxide to methane with hydrogen as an electron donor?
Which process involves the reduction of carbon dioxide to methane with hydrogen as an electron donor?
What is the primary process involved in the reduction of nitrite to nitrogen gas?
What is the primary process involved in the reduction of nitrite to nitrogen gas?
Where does acetogenesis occur, competing with methanogenesis?
Where does acetogenesis occur, competing with methanogenesis?
What process involves the oxidation of ammonia to nitrite and then to nitrate?
What process involves the oxidation of ammonia to nitrite and then to nitrate?
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Study Notes
Microbial Processes in Nutrient Cycling
- Methane hydrates found in the Arctic and marine sediments can absorb and release methane, fueling deep-sea ecosystems called cold seeps.
- Shallow coastal sediment methane hydrates are sensitive to seasonal changes in bottom water temperature, with methane bubbles observed when water temperatures warm by 1-2°C.
- All nutrient cycles are interconnected, with major changes in one cycle affecting the functioning of others, such as the close coupling of the carbon and nitrogen cycles.
- Methanogenesis, central to carbon cycling in anoxic environments, involves the reduction of carbon dioxide to methane with hydrogen as an electron donor, and often occurs in environments like freshwater lake sediments and the rumen.
- Acetogenesis, a H2-consuming process that competes with methanogenesis, occurs in environments like termite hindguts and the rumen, expanding the diet of termites.
- Nitrogen, comprising ~70% of the Earth's air, is recycled through processes like nitrogen fixation, denitrification, and ammonification, carried out by various microorganisms.
- Nitrification involves the oxidation of ammonia to nitrate, and anammox is beneficial in wastewater treatment by removing fixed nitrogen.
- Human activities impact the carbon and nitrogen cycles, with CO2 levels increasing by >40% since the Industrial Revolution, leading to radiative forcing and ocean acidification due to decreased pH from dissolved carbon dioxide.
- Mercury, a pollutant from various industries, enters aquatic environments as Hg2+ and undergoes microbial transformations, including methylation to yield toxic methylmercury that accumulates in fish tissues.
- Some bacteria can convert toxic forms of mercury to nontoxic or less toxic forms using specialized enzymes and genes, contributing to mercury resistance.
- Mercury resistance mechanisms involve the cleavage of methylmercury to less toxic forms and the reduction of Hg2+ to Hg0, often carried on plasmids or transposons.
- The microbial transformations of mercury, including methylation and reduction, have significant environmental implications due to the toxicity and accumulation of methylmercury in aquatic systems.
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