Which structures are present in the cytoplasm of both prokaryotes and eukaryotes?

Ribosomes are present in the cytoplasm of both prokaryotes and eukaryotes because they are essential cellular machinery responsible for protein synthesis. Their fundamental role in translating messenger RNA (mRNA) into proteins makes them crucial for all living cells, regardless of their classification as prokaryotic or eukaryotic.

In prokaryotes, ribosomes float freely in the cytoplasm as they lack membrane-bound organelles, while in eukaryotes, they can be found both free in the cytoplasm and attached to the endoplasmic reticulum, contributing to the rough ER's function. This distinction in location does not alter their primary function, which remains the same across both cell types.

Other cellular structures mentioned do not share this universality. Mitochondria and the Golgi apparatus are specific to eukaryotic cells, serving distinct roles such as energy production and processing and sorting proteins, respectively. The nuclear envelope, being a feature specific to eukaryotic cells, marks the boundary of the nucleus, absent in prokaryotes, which lack a defined nucleus. Thus, ribosomes stand out as the common structure found in both prokaryotic and eukaryotic cytoplasm.