Final answer:
Polypeptides are formed by joining amino acids in ribosomes through dehydration synthesis.
Step-by-step explanation:
The process of joining amino acids through dehydration synthesis to form long chains or polymers takes place in the ribosomes of a cell.
Ribosomes are responsible for protein synthesis, which involves the decoding of mRNA into a polypeptide product. Ribosomes catalyze the formation of peptide bonds between amino acids, resulting in the formation of polypeptides.