Final answer:
A synthesis reaction is when two or more simple substances combine to form a more complex product, such as when two amino acids bond to form a dipeptide, which is answer C.
Step-by-step explanation:
Which of the following is a synthesis reaction? The correct answer is C) Two amino acids are bonded together to form a dipeptide. In the context of amino acids, when a carboxyl group of one amino acid reacts with the amine group of another, a peptide bond is formed, releasing a water molecule in a process known as dehydration synthesis. This reaction results in the formation of a dipeptide, which is the joining of two amino acid units. Such reactions are central to the formation of proteins, as they can continue to bond amino acids into long polypeptide chains.