What is a plasmid in prokaryotes?

• A. A small circular DNA molecule independent of the main chromosome
• B. A large linear chromosome
• C. A lipid vesicle for storing nutrients
• D. A photosynthetic pigment

Answer: (A)

Plasmids are small circular DNA molecules that exist independently of the main chromosomal DNA in many prokaryotes. They replicate on their own and often carry accessory genes that provide advantages in certain conditions, such as antibiotic resistance or the ability to metabolize unusual substances. They’re much smaller than the main chromosome and are not essential for survival under normal conditions, but they can enhance fitness when present. The other descriptions describe something that is not a small, autonomous DNA element: the main chromosome in prokaryotes is large and contains essential genes, plasmids are separate circular DNA; a lipid vesicle is a membrane-bound storage structure; a photosynthetic pigment is a light-absorbing molecule, not DNA.