80S Ribosomes in Eukaryotic Cytoplasm

Steps:

• Identify ribosome types: 80S ribosomes consist of 60S and 40S subunits, typical of eukaryotes.
• Locate in eukaryotes: 80S ribosomes synthesize proteins in the eukaryotic cytoplasm for cytosolic functions.
• Contrast with organelles: Chloroplasts and mitochondria contain 70S ribosomes (30S + 50S subunits) from bacterial ancestry.
• Contrast with prokaryotes: Prokaryotic cytoplasm uses 70S ribosomes for all protein synthesis.

Why C is correct:

• 80S ribosomes are defined as the eukaryotic cytoplasmic type, per standard cell biology classification of ribosomal sedimentation coefficients.

Why the others are wrong:

• A includes prokaryotic cytoplasm (70S ribosomes) and chloroplasts (70S), excluding only mitochondria but still incorrect.
• B includes chloroplasts (70S) and prokaryotic cytoplasm (70S), ignoring eukaryotic cytoplasm.
• D specifies mitochondria, which house 70S ribosomes, not 80S.

Final answer: C