Multiple Choice
Why is the nitrogen cycle important to humans?
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35. Soil
Nitrogen Fixation
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How do most plants obtain the nitrogen they need for growth?
A
By directly fixing atmospheric nitrogen ($N_2$) through their roots
B
By absorbing nitrate and ammonium ions from the soil
C
By absorbing nitrogen gas ($N_2$) directly from the air through their leaves
D
By producing nitrogen through photosynthesis
Verified step by step guidance1
Understand that nitrogen is an essential nutrient for plants, as it is a key component of amino acids, proteins, and nucleic acids.
Recognize that most plants cannot directly use atmospheric nitrogen ($N_2$) because it is highly stable and requires conversion into a usable form.
Learn that nitrogen fixation is primarily carried out by certain bacteria (e.g., Rhizobium) in the soil or in symbiotic relationships with plants, converting $N_2$ into ammonia ($NH_3$).
Understand that plants absorb nitrogen primarily in the form of nitrate ($NO_3^-$) and ammonium ($NH_4^+$) ions from the soil through their roots.
Note that photosynthesis does not produce nitrogen; it is a process that converts light energy into chemical energy stored in glucose, and nitrogen must be obtained externally from the soil.
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