Which part of a plant serves as a home for nitrogen-fixing
cteria?
a. leaves
b. nodules
c. thorns
d. stems

Option B) Nodules.

Explanation:It is impossible for plants to fix atmospheric nitrogen(nitrogen present in soil) and hence they absorb nitrogen from the soil in the form of nitrates and ammonium.Plant absorbs nitrogen from soil through nodules present on roots.In case of leguminous(pulses) plant roots of the plant form a symbiotic association with nitrogen-fixing bacteria for example- Rhizobium.On the other hand if nitrates is directly absorbed by the plant, it is taken up by nitrate transporters which uses a proton gradient to power the nitrate to get transported.Absorbed nitrogen is transferred from root to shoot by xylem.

Result: Option B) is the correct answer.