Final answer:
The nucleolus is the structure in an interphase cell that contains ribosomal RNA and proteins for the formation of ribosomes. It is responsible for assembling ribosomal subunits which are then transported to the cytoplasm to direct protein synthesis.
Step-by-step explanation:
The nucleolus is the structure in an interphase cell that contains ribosomal RNA and proteins for the formation of ribosomes. It is a dark-staining area within the nucleus and is responsible for assembling ribosomal subunits. These subunits are then transported out of the nucleus into the cytoplasm through nuclear pores, where they direct protein synthesis.