Organelles and structures containing or synthesizing rRNA

Steps:

• rRNA forms the core of ribosomes, enabling protein synthesis in specific cellular locations.
• Chloroplast (1) has 70S ribosomes with its own rRNA transcribed from chloroplast DNA.
• Mitochondrion (2) has 70S ribosomes with rRNA from mitochondrial DNA.
• Rough ER (3) has attached cytoplasmic ribosomes, but no independent rRNA synthesis.
• Nucleus (4) contains the nucleolus, where all eukaryotic rRNA is transcribed and ribosomal subunits assemble.

Why A is correct:

• A includes 1, 2, and 4, which are sites of rRNA transcription and ribosome assembly, per eukaryotic cell biology.

Why the others are wrong:

• B omits 2 and 4, excluding key organelles with independent rRNA.
• C includes 3, but rough ER relies on nuclear rRNA, not producing its own.
• D omits 1 and includes 3, ignoring chloroplast rRNA and overincluding rough ER.

Final answer: A