Question

question 17 of 50
why are bacteria required in the nitrogen cycle?
a. nitrogen needs to be fixed before it is used by plants.
b. the xylem in plants cannot function without bacteria.
c. plant dna can only be transmitted by bacteria.
d. plants need to pull nitrogen directly from the air.

Explanation:

In the nitrogen cycle, nitrogen - fixing bacteria convert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) or other nitrogen - containing compounds that plants can use. Plants cannot directly use atmospheric nitrogen. Option B is incorrect as xylem is for water and mineral transport, not related to nitrogen use in this context. Option C is wrong because plant DNA can be transmitted without bacteria in terms of basic genetic processes. Option D is incorrect as plants cannot pull nitrogen directly from the air without the help of nitrogen - fixing bacteria.

Answer:

A. Nitrogen needs to be fixed before it is used by plants.