What is a plasmid?

A plasmid is best defined as a small ring of DNA that is separate from the bacterial chromosome. These plasmids are naturally occurring in many bacteria and serve various functions, including the ability to replicate independently of chromosomal DNA, carry genes that can provide advantages such as antibiotic resistance, and facilitate gene transfer between bacteria through processes like conjugation.

Plasmids are distinct from chromosomal DNA due to their circular structure and smaller size. They can be easily manipulated in genetic engineering, making them valuable tools in biotechnology and research. This characteristic sets plasmids apart from the other options, which do not accurately describe plasmids and their role within bacterial cells or genetic research.