How Is Atmospheric Nitrogen Converted to a Usable Form in the Biosphere

Multiple Choice

How is atmospheric nitrogen converted to a usable form in the biosphere?

A) It is absorbed into plants via stomata and converted within the plant to a usable form.
B) Atmospheric nitrogen is directly available to plants and animals.
C) Bacteria within root nodules of legumes chemically combine the atmospheric nitrogen into nitrates and ammonia.
D) Atmospheric nitrogen is completely unavailable to plants and animals and,as a result,synthetic fertilizers must be used.