Multiple Choice
Which process is primarily responsible for returning nitrogen to the atmosphere in the nitrogen cycle?
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35. Soil
Nitrogen Fixation
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What is the role of nitrogen-fixing bacteria in the nitrogen cycle?
A
They break down dead organic matter to release nitrogen back into the atmosphere.
B
They convert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$), making nitrogen available to plants.
C
They convert ammonia ($NH_3$) into nitrate ($NO_3^-$) through nitrification.
D
They absorb excess nitrogen from the soil to prevent toxicity.
Verified step by step guidance1
Nitrogen-fixing bacteria play a crucial role in the nitrogen cycle by converting atmospheric nitrogen ($N_2$), which is inert and unavailable to most organisms, into ammonia ($NH_3$). This process is called nitrogen fixation.
Atmospheric nitrogen ($N_2$) is highly stable due to its triple bond, making it inaccessible to plants. Nitrogen-fixing bacteria, such as those in the genus Rhizobium, possess the enzyme nitrogenase, which facilitates the conversion of $N_2$ into $NH_3$.
The ammonia ($NH_3$) produced by nitrogen-fixing bacteria can be further utilized by plants directly or converted into other nitrogen compounds, such as nitrate ($NO_3^-$), through subsequent processes like nitrification.
Nitrogen fixation is essential for maintaining the nitrogen cycle because it provides a usable form of nitrogen for plants, which is a critical nutrient for their growth and development.
This process is symbiotic in some cases, as nitrogen-fixing bacteria often form mutualistic relationships with plants, particularly legumes, by inhabiting root nodules and providing nitrogen in exchange for carbohydrates and a suitable environment.
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