Question

question 3 of 10
where does nitrogen from the atmosphere go before it enters a plant?
a. the nitrogen goes through the roots into the soil.
b. the nitrogen fixes into carbon dioxide.
c. the nitrogen atoms of the atmosphere never enter the plant.
d. the nitrogen goes into the nodules of the plant.

Explanation:

Plants cannot directly use atmospheric nitrogen (\(N_2\)). Nitrogen - fixing bacteria in the nodules of leguminous plants (and some other plants) convert atmospheric nitrogen into ammonia (\(NH_3\)) or other nitrogen - containing compounds that plants can absorb and use. So nitrogen from the atmosphere first goes into the nodules of the plant before being used by the plant.

• Option A: Nitrogen does not go through the roots into the soil first. The roots are the entry point for the already - fixed nitrogen compounds (not the direct entry of atmospheric \(N_2\)).
• Option B: Nitrogen does not fix into carbon dioxide. Carbon dioxide is involved in photosynthesis (\(CO_2\) is taken in by plants for making organic compounds like glucose), and nitrogen fixation is a separate process.
• Option C: Nitrogen atoms from the atmosphere do enter the plant (after being fixed by bacteria).

Answer:

D. The nitrogen goes into the nodules of the plant.