Which of the following describes small circular pieces of extrachromosomal DNA that contain few genes?

Plasmids are small, circular pieces of extrachromosomal DNA that are distinct from chromosomal DNA. They typically contain a limited number of genes, often related to functions such as antibiotic resistance or the production of specific proteins, which can be advantageous for the cell. Plasmids are naturally found in bacteria and can replicate independently of chromosomal DNA, allowing for their transfer between bacteria through processes like conjugation. This characteristic enables genetic diversity and adaptability among bacterial populations.

In contrast, chromosomes are larger structures that contain the genetic blueprint of the organism and are organized into linear or circular forms, depending on whether the organism is eukaryotic or prokaryotic. Chromatids refer to the identical halves of a replicated chromosome, which are involved in cell division, and do not function as independent pieces of DNA. Ribosomes are not DNA; they are the cellular machinery responsible for protein synthesis, composed of RNA and proteins. These distinctions clarify why plasmids are accurately described by the given definition in the question.