Multiple Choice
Which of the following pathways indicates how nitrogen is added to the largest nitrogen reservoir (the atmosphere)?
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35. Soil
Nitrogen Fixation
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How do humans primarily obtain the nitrogen necessary for building proteins and nucleic acids?
A
By consuming plants and animals that contain organic nitrogen compounds
B
By absorbing nitrogen through the skin from soil
C
By directly inhaling nitrogen gas ($N_2$) from the atmosphere
D
By converting atmospheric nitrogen into ammonia in their own cells
Verified step by step guidance1
Understand the role of nitrogen in biological systems: Nitrogen is a key element in amino acids (building blocks of proteins) and nucleotides (building blocks of nucleic acids). Humans need nitrogen to synthesize these molecules.
Recognize that atmospheric nitrogen ($N_2$) is highly stable and cannot be directly used by humans or most organisms. It requires conversion into a biologically usable form, such as ammonia ($NH_3$) or nitrate ($NO_3^-$), through processes like nitrogen fixation.
Learn that humans cannot perform nitrogen fixation themselves. Instead, they rely on consuming organic nitrogen compounds found in plants and animals. These compounds are already in a form that can be metabolized and used to build proteins and nucleic acids.
Understand the role of plants and animals in the nitrogen cycle: Plants absorb nitrogen from the soil in the form of nitrates or ammonium, which are converted into organic nitrogen compounds. Animals obtain nitrogen by consuming plants or other animals.
Conclude that humans primarily obtain nitrogen by consuming plants and animals that contain organic nitrogen compounds, as this is the only biologically accessible method for humans to acquire nitrogen for their metabolic needs.
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