RNA interference takes place as cellular defense in:

The correct answer is Option (3) → All eukaryotic organisms

RNA interference (RNAi) is a process in which a complementary double-stranded RNA binds to a specific mRNA and stops it from being translated. This silences the gene. The complementary RNA can come from an infection by RNA viruses or from mobile genetic elements (transposons). It has been used to protect tobacco roots from a nematode.

(1) All prokaryotic organisms — Incorrect. The cellular defence by RNAi is described for eukaryotes, not for prokaryotes.

(2) All cyanobacteria — Incorrect. Cyanobacteria are prokaryotes, so the same reason applies.

(3) All eukaryotic organisms — Correct. RNAi takes place in all eukaryotic organisms as a method of cellular defence.

(4) All viruses — Incorrect. Viruses are not cells. RNAi is a defence of the host cell. Viruses with an RNA genome can only be a source of the RNA that sets it off.

NCERT Extract:
Biotechnological Applications in Agriculture – …