OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What describes the function of a plasmid?

It is a part of ribosomal RNA
It contains essential genes for metabolism
It houses non-essential genes like drug resistance
It aids in the formation of the cell membrane

The correct answer is: It houses non-essential genes like drug resistance

A plasmid is a small, circular piece of DNA commonly found in bacteria and some other organisms. Its primary function is to carry non-essential genes that can provide beneficial traits to the organism, such as antibiotic resistance, which can be crucial for survival in environments where such drugs are present. These genes allow bacteria to adapt and evolve, increasing their chances of survival under selective pressures. While essential genes for metabolism and functions related to ribosomal RNA are critical for the basic life processes of the cell, plasmids typically do not encode these essential functions. Additionally, plasmids do not play a role in the formation of the cell membrane. Their main significance lies in their ability to confer traits that can help an organism survive in challenging conditions, particularly in relation to antimicrobial resistance.