A plasmid is a small, circular piece of DNA found in many bacteria. Unlike the main DNA that carries essential genetic information, plasmids often carry extra genes that can provide advantages, such as antibiotic resistance. This ability to share plasmids among bacteria allows them to quickly adapt to new environments or threats. Scientists use plasmids in genetic engineering to introduce new traits into organisms. By inserting a gene of interest into a plasmid, researchers can transfer it into a host cell, such as a bacterium or plant. This technique is crucial for developing new medicines, improving crops, and studying gene functions.