Final answer:
Ribosomes are responsible for D) protein synthesis in cells.
Step-by-step explanation:
Ribosomes
Ribosomes are the cellular structures responsible for protein synthesis.
When viewed through an electron microscope, ribosomes appear either as clusters or single, tiny dots floating freely in the cytoplasm.
They may be attached to the cytoplasmic side of the plasma membrane or the cytoplasmic side of the endoplasmic reticulum.