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

Which components do bacterial cells contain?

1. Only ribosomes and DNA

2. Chromosomal DNA and a nucleus

3. Chromosomal DNA, plasmids, and a cell membrane

4. Only plasma membranes and cytoplasm

The correct answer is: Chromosomal DNA, plasmids, and a cell membrane

Bacterial cells are characterized by specific structural components that contribute to their function and survival. The correct choice highlights that bacterial cells contain chromosomal DNA, plasmids, and a cell membrane. Chromosomal DNA is the main genetic material in bacteria, typically organized in a single, circular chromosome that resides in a region called the nucleoid. This DNA contains essential genes necessary for the cell's functioning and reproduction. Plasmids are extra-chromosomal DNA molecules that can carry additional genes, often providing advantageous traits such as antibiotic resistance. They can replicate independently of the chromosomal DNA and are vital for horizontal gene transfer between bacteria. The cell membrane, also known as the plasma membrane, surrounds the bacterial cell and regulates the movement of substances in and out of the cell. It plays a crucial role in maintaining the internal environment of the cell. In contrast, the other choices do not accurately represent the structure of bacterial cells. For instance, bacterial cells lack a nucleus, which is a characteristic of eukaryotic cells (this rules out the option that mentions a nucleus). Additionally, mentioning "only" components like ribosomes and DNA or "only" plasma membranes and cytoplasm indicates an incomplete understanding of bacterial cell structure, as they contain more than just these components