Which cellular structure is found in bacterial cells?

Bacterial cells are prokaryotic organisms, meaning they lack a defined nucleus and membrane-bound organelles that are characteristic of eukaryotic cells. However, ribosomes are essential cellular structures present in both prokaryotic and eukaryotic cells, as they play a crucial role in protein synthesis. Bacterial ribosomes, while structurally different from those found in eukaryotic cells, are vital for translating messenger RNA into proteins, which is a fundamental process for all cellular activity and survival.

In contrast, other choices such as the nucleus, mitochondria, and endoplasmic reticulum are all features of eukaryotic cells. The nucleus houses the cell's genetic material, mitochondria are involved in energy production, and the endoplasmic reticulum is crucial for the synthesis and transport of proteins and lipids within eukaryotic cells. Since bacteria do not possess these membrane-bound organelles, ribosomes stand out as the key cellular structure found in bacterial cells.