Final answer:
A cell with a predominance of free ribosomes is likely producing cytoplasmic proteins, as free ribosomes synthesize proteins that stay within the cell. In contrast, cells with extensive rough ER produce proteins for secretion or the endomembrane system, and cells with abundant smooth ER usually produce steroid hormones. The correct option is B) producing primarily cytoplasmic proteins.
Step-by-step explanation:
A cell with a predominance of free ribosomes is most likely producing primarily cytoplasmic proteins. Free ribosomes are responsible for synthesizing proteins that function within the cytosol of a cell. Conversely, ribosomes attached to the rough endoplasmic reticulum (RER) are typically involved in producing proteins for secretion, incorporation into cell membranes, or for the endomembrane system. Cells that secrete proteins, like enzyme-secreting cells, will have an abundance of RER to facilitate protein folding and modification. On the other hand, a cell with an extensive smooth endoplasmic reticulum is likely involved in creating steroid hormones. Furthermore, in cells that produce a significant amount of extracellular matrix, you would expect their ribosomes to synthesize large quantities of specific proteins required for that matrix.
Therefore, for a cell that functions to synthesize proteins for export, the newly made protein would start synthesis on the RER, then enter the lumen where it is modified, before being packaged into vesicles and sent to the Golgi apparatus for further processing and sorting. The correct option is B) producing primarily cytoplasmic proteins.