Question

an important organelle is missing from this image of a eukaryotic cell undergoing protein synthesis. this organelle is not surrounded by a membrane but sits in the nucleus. it produces ribosomal subunits from proteins and ribosomal rna, which is exported into the cell proper. it is key to the process of protein synthesis taking place at ribosomes. what is this organelle?
a centriole
b centrosome
c mitochondria
d nucleolus

Explanation:

The organelle described produces ribosomal subunits, is in the nucleus, not membrane - bound, and is key for protein synthesis at ribosomes. The nucleolus (option D) functions in producing ribosomal RNA and ribosomal subunits, matching the description. Centriole (A) is for cell division, centrosome (B) organizes microtubules, and mitochondria (C) is for energy production, so they don't fit.

Answer:

D. nucleolus