Final answer:
Restriction endonucleases, or restriction enzymes, are obtained from bacterial cells and are widely used in recombinant DNA technology. These enzymes recognize and cleave specific DNA sequences, and more than 800 restriction endonucleases have been discovered so far.
Step-by-step explanation:
Restriction endonucleases, also known as restriction enzymes, are most commonly obtained from bacterial cells. These enzymes have evolved in bacteria as a defense mechanism against invading phage and are used extensively in recombinant DNA technology. More than 800 restriction endonucleases have been discovered so far, and each enzyme can recognize and cleave specific DNA sequences. Therefore, the correct answer is option (b) Bacterial cells.