Which organelle is primarily involved in protein synthesis?

The ribosome is the organelle primarily involved in protein synthesis due to its essential role in translating messenger RNA (mRNA) into polypeptide chains, which eventually fold into functional proteins. Ribosomes can either be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, where they facilitate the assembly of amino acids in accordance with the genetic instructions carried by mRNA.

It is important to note the functions of the other organelles in the context of cellular activities. Chloroplasts are involved in photosynthesis, converting sunlight into energy and producing sugars. Mitochondria are primarily responsible for energy production through the process of cellular respiration, generating ATP. The Golgi apparatus plays a key role in modifying, sorting, and packaging proteins and lipids for secretion or for use within the cell. While each of these organelles has a distinct function, it is the ribosome that directly carries out the process of synthesizing proteins, making it the correct answer.