Ribosomes are responsible for

• A. DNA replication
• B. Protein synthesis
• C. Lipid synthesis
• D. Photosynthesis

Answer: (B)

Ribosomes are the cellular machinery that translate genetic information into proteins. They read messenger RNA sequences and, with transfer RNAs bringing specific amino acids, assemble them into a polypeptide chain. This is the process of protein synthesis, so the correct choice is protein synthesis.

DNA replication is carried out by DNA polymerases and other enzymes in the nucleus, not by ribosomes. Lipid synthesis happens mainly in the smooth endoplasmic reticulum and cytosol with enzymes that assemble fatty acids and other lipids. Photosynthesis takes place in chloroplasts using light-driven reactions to convert CO2 and water into glucose. Ribosomes are not performing these processes; their job is to make proteins.