High School Biology : Understanding the Nitrogen Cycle

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding The Nitrogen Cycle

Why can plants not utilize naturally occurring nitrogen gas?

Possible Answers:

Most of the nitrogen is stored as nitrate (NO3-)

There are insufficient amounts available in the atmosphere

Plants cannot break the triple bond between the two nitrogen atoms

Lack of nitrogen-fixing bacteria

Correct answer:

Plants cannot break the triple bond between the two nitrogen atoms

Explanation:

Like carbon, nitrogen is one the most abundant elements in biotic factors. Nitrogen gas is highly abundant in our atmosphere, however it cannot be utilized by humans and plants while in its gaseous state because of the very strong triple bond between the two nitrogen atoms. For plants to use nitrogen, they must have it converted to ammonium or nitrate by bacteria found in the soil and roots. The process of converting nitrogen gas to ammonium is called nitrogen fixation. Decomposition of plants and animals also releases ammonium into the ground. This ammonium can be further converted to nitrate with the help of nitrifying bacteria. Returning nitrogen back to the atmosphere is called denitrification. This process is carried out by some bacteria found in lakes and swamps. These bacteria are anaerobic, so they use the nitrate and release nitrogen gas into the air.

Example Question #2 : Understanding The Nitrogen Cycle

Which of the following is most directly responsible for nitrogen fixation?

Possible Answers:

Plant roots

Animals

Humans

Sunlight

Bacteria

Correct answer:

Bacteria

Explanation:

Nitrogen fixation is mostly done by bacteria living in the soil. Plants need nitrogen to grow, but they cannot use it straight from the atmosphere or as ammonia from the soil.

Humans and animals largely obtain their necessary nitrogen by consuming plants, and do not fix nitrogen or rely directly on bacteria for the process.

Example Question #3 : Understanding The Nitrogen Cycle

Which of the following biological processes is not linked to the nitrogen cycle?

Possible Answers:

Nitrogen fixation

Assimilation by plants

Ammonification

Denitrification

Condensation

Correct answer:

Condensation

Explanation:

Condensation is not part of the nitrogen cycle. It is part of the water cycle, during which water molecules condense together in the atmosphere to form clouds.

Example Question #4 : Understanding The Nitrogen Cycle

Nitrification is the process of turning __________ into __________.

Possible Answers:

animal waste . . . NH3

NO3- . . . plants

NO2- . . . NO3-

N2 . . . NH3

NO3- . . . N2

Correct answer:

NO2- . . . NO3-

Explanation:

Nitrification is the process by which nitrite (NO2-) is converted to nitrate (NO3-). This is the final step required in the processes used to oxidize nitrogen wastes (ammonia) to usable nitrate ions.

The conversion of gaseous nitrogen to ammonia (N2 to NH3) describes nitrogen fixation, and is usually done by nitrogen-fixing bacteria. 

The conversion of nitrate to plant matter (NO3- to plants) describes the process of assimilation. 

The conversion of nitrate to gaseous nitrogen (NO3- to N2) describes denitrification, and is performed by denitrification bacteria. 

The conversion of animal waste to NHdescribes ammonification, and is accomplished by saprobiotic (decomposing) bacteria.

Example Question #5 : Understanding The Nitrogen Cycle

How do plants obtain nitrogen? 

Possible Answers:

Plants do not use nitrogen 

From the soil using their roots 

From the atmosphere 

From water 

Correct answer:

From the soil using their roots 

Explanation:

The nitrogen in plants comes from the soil. Bacteria in the soil take nitrogenous wastes and convert it into forms of nitrogen that plants can use. Plants then take up nitrogen through their roots. 

Example Question #6 : Understanding The Nitrogen Cycle

What is the largest natural reservoir nitrogen on earth?

Possible Answers:

The hydrosphere

The sun

The Earth's atomosphere

The biosphere

The geosphere

Correct answer:

The Earth's atomosphere

Explanation:

The atmosphere is composed of 78% nitrogen gas and while by mass the atmosphere is less massive than the all the other choices the other choices are not primarily composed of nitrogen and contain relatively little compared to the nitrogen in the atmosphere.

Example Question #7 : Understanding The Nitrogen Cycle

Is the majority of the Earth's nitrogen immediately available for use by plants and other living organisms? Why?

Possible Answers:

No, because nitrogen gas is not able to be converted to other forms.

Yes, because the majority of the world's nitrogen is present in ammonium

No, most of it exists as inorganic nitrogen gas and is not immediately usable to most organisms.

No, because the majority of the world's nitrogen is locked in geological reservoirs  

Yes, because the nitrogen gas that composes the atmosphere is usable to most organisms.

Correct answer:

No, most of it exists as inorganic nitrogen gas and is not immediately usable to most organisms.

Explanation:

Since the nitrogen gas that composes 78% of the atmosphere is not immediately usable to all organisms except for nitrogen-fixing organisms the nitrogen that composes the Earth's major nitrogen reserve is not immediately usable to most organisms. 

Example Question #571 : High School Biology

Which of the following is not a way in which nitrogen is fixed?

Possible Answers:

Lightening 

Deposition

Nitrogen-fixing bacteria 

Volatilization

The Haber-Bosch process

Correct answer:

Volatilization

Explanation:

Volatilization is a process by which fixed nitrogen is released back into the atmosphere as  gas. 

Example Question #572 : High School Biology

What is the main way that fixed nitrogen is released back into the atmosphere?

Possible Answers:

Denitrifying microbes

Volatilization

Runoff

Erosion

Crop harvests

Correct answer:

Denitrifying microbes

Explanation:

Only two options here actually lead to the conversion of fixed nitrogen to atmospheric nitrogen, volatilization and denitrification of which denitrification is a relatively rapid process carried out by numerous denitrifying microbes thus making it the greater contributor to the return of nitrogen to the atmosphere from fixed nitrogen. 

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