Question 1

Nitrogen fixation in the soil is carried out by

Accepted Answer

Nitrogen fixation in the soil is primarily carried out by cyanobacteria, which are able to convert atmospheric nitrogen into a form that plants can use. While other bacteria and fungi may play a role in the nitrogen cycle, cyanobacteria are the main group of organisms responsible for nitrogen fixation in soil.

Question 2

The burning of fossil fuels affects the nitrogen cycle by increasing atmospheric

Accepted Answer

Burning fossil fuels releases nitrogen oxides (NOx), which can react with other chemicals in the air to form nitric oxide (NO). This can then react with other compounds to form nitrogen dioxide (NO2), which is a component of smog and a major contributor to air pollution. NOx emissions from fossil fuel combustion can therefore increase atmospheric nitric oxide levels, affecting the nitrogen cycle.

Question 3

What form of nitrogen reacts with water in the air to form nitrates that fall to the ground during precipitation?

Accepted Answer

The answer of What form of nitrogen reacts with water...

Question 4

Choose the correct process of nitrogen fixation.

Accepted Answer

Nitrogen fixation is the process of converting atmospheric nitrogen into a form usable by plants. The correct process of nitrogen fixation involves the conversion of atmospheric nitrogen (N₂) into ammonia (NH3) through the process of nitrogenase (F1F1F1S1). This process can be carried out by free-living soil bacteria (NO₃-) or by symbiotic bacteria living in root nodules of leguminous plants (NH₃+ or NH₄+). Therefore, Option B is the best choice as it includes both free-living soil bacteria and symbiotic bacteria in the correct process of nitrogen fixation.

Question 5

Which is NOT an example of a major human alteration to the global nitrogen cycle?

Accepted Answer

The answer of Which is NOT an example of a...

Question 6

Nitrogen mineralization in the soil is primarily carried out by

Accepted Answer

Nitrogen mineralization is the process by which organic nitrogen compounds in the soil are broken down into inorganic nitrogen by decomposers, such as bacteria and fungi. Producers, consumers, and nitrogen-fixing plants do not directly carry out this process. Cyanobacteria may fix nitrogen in certain environments, but are not the primary drivers of nitrogen mineralization in the soil.

Question 7

Describe the path of nitrogen as it moves from the atmosphere to the soil, plants, animals, and back to the atmosphere. Describe each process and the location and the form of nitrogen (including chemical formula) at each step.

Accepted Answer

The answer of Describe the path of nitrogen as it...

Question 8

Nitrogen mineralization is the process by which

Accepted Answer

Nitrogen mineralization is the process where soil microbes decompose organic nitrogen from dead organisms or organic matter, converting it into inorganic nitrogen forms (such as ammonium), which can then be used by plants. This is a crucial step in the nitrogen cycle, making nitrogen available to plants in a form they can absorb.

Question 9

The chemical process NH₄+ $\rightarrow$ NO₂- $\rightarrow$ NO₃-, is known as

Accepted Answer

The chemical process described involves the conversion of amino groups (NH₄+ and NO₂-) into nitrate ions (F1F1F10 and NO₃-), which is a part of the nitrogen cycle and specifically known as nitrification. The other options refer to other parts of the nitrogen cycle or processes that do not involve the conversion of amino groups into nitrate ions.

Question 10

Where does phosphorus originate in the phosphorus cycle?

Accepted Answer

Phosphorus in the phosphorus cycle originates from rocks containing phosphate, which undergo weathering to release phosphate into the soil and water. This phosphate is then taken up by plants and enters the food chain. Eventually, it returns to the soil and water through decomposition of organic matter or excretion by animals.

Question 11

Dead zones are formed when rivers that empty into oceans carry excess phosphorus and nitrate runoff. These dead zones are caused by

Accepted Answer

Dead zones are caused by an excess of nutrients, particularly phosphorus and nitrogen, which leads to the growth of algae, creating algal blooms. As the algae die and decompose, it consumes oxygen in the water, creating hypoxic or anoxic conditions that cannot support most marine life. Therefore, algal blooms are the primary cause of dead zones.

Question 12

Which of the following is NOT a critical phosphorus-containing structure for organisms?

Accepted Answer

While phosphorus is involved in the production of lipids, it is not a critical component of the structure of lipids. Therefore, D is the correct answer as the other options all contain critical phosphorus-containing structures such as bones, nucleic acids, ATP, and teeth.

Question 13

Denitrification occurs under _____ conditions.

Accepted Answer

Denitrification is a process carried out by bacteria in anaerobic conditions where nitrate (NO3-) is converted to nitrogen gas (N2) and nitrous oxide (N2O) is produced as an intermediate. This process requires the absence of oxygen. Therefore, denitrification only occurs under anaerobic conditions.

Question 14

Denitrification is described by

Accepted Answer

Denitrification is the process where nitrate (NO₃⁻) is reduced and ultimately produces nitrogen gas (N₂) through intermediate gaseous nitrogen oxide products like nitrous oxide (N₂O).

Question 15

Phosphatizing bacteria convert phosphorus compounds into

Accepted Answer

Phosphatizing bacteria are known to convert phosphorus compounds into phosphate ions.

Question 16

(Figure 21.8) The figure shows results of nitrogen addition in eight sites around the United States. What do these results tell us about limiting resources at the sites? What did researchers conclude about declines in species richness?

Accepted Answer

The answer of  (Figure 21.8) The figure shows results...

Question 17

What is the main avenue by which phosphorus returns to the ocean?

Accepted Answer

The main avenue by which phosphorus returns to the ocean is through surface runoff, as it can be carried by water from agricultural and urban areas. Phosphorus can also be deposited in the ocean through dust, but this is not the primary pathway. Dissolved phosphorus in rainwater and wastewater can also contribute to the phosphorus in the ocean, but these sources are not as significant as surface runoff.

Question 18

Nitrogen-fixing plants such as soybeans are able to convert

Accepted Answer

Nitrogen-fixing plants such as soybeans are able to convert atmospheric nitrogen to nitrate and ammonium. This process is carried out with the help of symbiotic bacteria called Rhizobia which colonize the roots of the plants and assist with nitrogen fixation.

Question 19

What is the largest pool of nitrogen in the global nitrogen cycle?

Accepted Answer

The atmosphere contains 78% nitrogen gas, making it the largest pool of nitrogen in the global nitrogen cycle. While nitrogen is also found in terrestrial biomass, oceans, and soil, the majority of it exists in the atmosphere as N2 gas. The other forms of nitrogen are either taken up by plants and organisms or released through natural processes such as denitrification and nitrogen fixation.

Question 20

In what form does phosphorus move through the environment?

Accepted Answer

Phosphorus moves through the environment as phosphate ions (PO4-), which are represented by PO₄³-.

Quiz 21: Movement of Elements in Ecosystems