Which statement is true about a nucleus

Option (d).

Explanation:

The well defined nucleus is absent in prokaryotes whereas the well defined nucleus covered with nuclear envelope is present in eukaryotes. The site of replication and transcription is the nucleus in the living organism.

The nucleus contains the double membrane structure. Outer membrane and inner membrane covers the nucleus. Nucleus also contains the nuclear pore through which molecules can move inside and outside of the nucleus and the cytoplasm.

Thus, the correct answer is option (d).

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.