Biology · Cell: The Unit of Life · NEET
A plasmid is DOUBLE-stranded. It is made of normal DNA, and all DNA is double-stranded. This is the exact NEET trap. In the 2016 paper, "single-stranded" was the WRONG feature you had to pick. So remember: plasmid = double-stranded, just like the main chromosome.
The genomic DNA is the bacterium's single main chromosome that carries the genes needed to live. The plasmid is small, extra DNA that sits OUTSIDE the genomic DNA. The cell can survive without the plasmid, but not without its genomic DNA. Both are circular and double-stranded, but the plasmid is much smaller and copies itself independently.
In bacteria a plasmid is CIRCULAR, forming a closed ring of DNA. The main bacterial chromosome is also circular. So both are ring-shaped, but the plasmid is the smaller ring lying free in the cytoplasm.
Yes. A plasmid has its own origin of replication, so it copies itself INDEPENDENTLY of the main chromosome. This is called autonomous or independent replication, and it is one of the key features NEET asks about. Some plasmids keep only 1-2 copies per cell, others 15-100.
The plasmid gives the bacterium extra phenotypic characters it would not otherwise have. The most famous example from NCERT is resistance to antibiotics. Plasmids can also be transferred from one bacterium to another, which spreads these traits. In higher classes, plasmids are used as vectors to carry foreign DNA in genetic engineering.
For NEET, treat plasmids as a feature of prokaryotes (bacteria). NCERT says "many bacteria have small circular DNA outside the genomic DNA... called plasmids." So if a question asks for a characteristic of prokaryotic cells, "they can have plasmids" is correct (tested in ReNEET 2026).
Which of the following is not a feature of the plasmids?
Which of the following are characteristics of prokaryotic cells? (a) Ribosomes are made of 50S and 30S subunits; (b) They can have plasmids; (c) They contain mesosome; (d) They have peroxisomes.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A plasmid is a small, extra ring of DNA inside many bacteria that sits outside the main chromosome and copies itself on its own. It gives the bacterium bonus traits like antibiotic resistance.
Four features: it is (1) circular, (2) double-stranded DNA, (3) extra-chromosomal (outside genomic DNA), and (4) capable of independent replication. It is also transferable between bacteria.
Because a plasmid replicates on its own and can be transferred, scientists use it as a vector to carry foreign DNA into a host bacterium. NCERT mentions plasmids are used to monitor bacterial transformation with foreign DNA.
No. The genomic DNA is essential, but plasmid DNA only adds extra characters like antibiotic resistance. A bacterium can survive without its plasmid, which is why plasmids are called extra-chromosomal.
It varies. Some plasmids keep only one or two copies per cell, while others have 15 to 100 copies, because the origin of replication controls the copy number.
