Antibiotics are substances produced by microorganisms that inhibit the growth of or destroy other microorganisms. They are used in the treatment of bacterial and fungal diseases. The correct option is D, products of metabolism in some bacteria.

Explanation:

Antibiotics are substances that are produced by microorganisms such as bacteria and fungi. These microorganisms produce antibiotics as a means of defending themselves against other microorganisms that may compete with them for food and other resources. Antibiotics can be used to treat bacterial and fungal infections in humans and animals.

Products of metabolism in some bacteria:

Antibiotics are produced by some bacteria as a result of their metabolic processes. These antibiotics are then released into the surrounding environment, where they can inhibit the growth of or destroy other microorganisms. Some examples of bacteria that produce antibiotics include Streptomyces and Bacillus.

Streptomyces:

Streptomyces is a genus of bacteria that is known for its ability to produce a wide range of antibiotics. These antibiotics include streptomycin, tetracycline, erythromycin, and chloramphenicol. Streptomycin is used to treat tuberculosis, while tetracycline is used to treat acne and other bacterial infections.

Bacillus:

Bacillus is another genus of bacteria that is known for its ability to produce antibiotics. Bacitracin is an antibiotic that is produced by Bacillus subtilis and is used to treat skin infections. Other antibiotics produced by Bacillus include polymyxin and neomycin.

Conclusion:

In conclusion, antibiotics are substances produced by microorganisms that inhibit the growth of or destroy other microorganisms. They are used in the treatment of bacterial and fungal diseases. Some antibiotics are produced by bacteria as a result of their metabolic processes. These antibiotics can be used to treat a wide range of infections in humans and animals.