Bacterial cell diagram: a cell with no nucleus
A bacterial cell diagram shows a cell wall on the outside, a cell membrane just inside it, and cytoplasm inside that. There is no nucleus. The genetic material is a single loop of DNA lying in the cytoplasm. There may also be plasmids, small extra rings of DNA. Ribosomes make the cell's proteins. Bacteria have no mitochondria and no chloroplasts.
Prokaryotic and eukaryotic cells
Biologists sort cells into two groups. Plant and animal cells are eukaryotic, which means their genetic material is wrapped inside a nucleus. Bacterial cells are prokaryotic. Their genetic material sits loose in the cytoplasm with nothing around it.
AQA also says bacterial cells are much smaller than plant and animal cells. AQA asks you to understand the scale of cells like these, using standard form where it helps. The magnification formula page shows how to turn a measured image into a real size.
What each part of a bacterium does
Cell wall and cell membrane
AQA describes a cell membrane surrounded by a cell wall. The membrane controls which substances cross into the cell. The wall is the outer layer around it. AQA says a cellulose wall strengthens plant and algal cells, but it does not say what a bacterial wall is made of.
Cytoplasm and ribosomes
The cytoplasm holds everything else. OCR Twenty First Century says microorganisms respire in the cytoplasm. Bacteria have no mitochondria. Edexcel lists ribosomes in bacteria. They build proteins, just as they do in your own cells.
The DNA loop and plasmids
The main genetic material is one loop of DNA. Edexcel calls it chromosomal DNA. Plasmids are small rings of DNA, and a cell can have one or more. Edexcel calls these plasmid DNA.
Flagella
Edexcel adds flagella to its list of bacterial parts. AQA and OCR do not mention them, and Edexcel does not say what they do.
How fast bacteria multiply
AQA GCSE Biology (8461) covers growing bacteria in the lab. A bacterium splits into two by simple cell division, called binary fission. With enough food and the right temperature, this can happen as often as once every 20 minutes.
School labs grow bacteria in a nutrient broth or on agar gel in a Petri dish, usually at 25°C. This part is in 8461 only, and Combined Science (8464) leaves it out.
Some bacteria respire without oxygen and make lactic acid. See the anaerobic respiration equation for how that works.
Common mistakes
- Drawing a nucleus. Bacteria are prokaryotic, so the DNA loop sits in the cytoplasm with no nucleus.
- Leaving out the cell wall. Bacteria have one, around the cell membrane, as AQA says.
- Adding mitochondria or chloroplasts. A bacterial cell has neither.
- Calling a plasmid the main DNA. The main genetic material is the single DNA loop, and plasmids are small extra rings.
The bacterial cell is one of the levels in Cell Builder, where you place the DNA loop and plasmids yourself. The biology hub links every cell page.
Questions people ask
Do bacteria have a cell wall?
Yes. AQA says bacterial cells have cytoplasm and a cell membrane surrounded by a cell wall. That puts bacteria alongside plants and algae as cells with a wall.
Where is the DNA in a bacterial cell?
In the cytoplasm. It forms one loop, and there may be plasmids as well. OCR Twenty First Century says the same: with no nucleus, the genetic material lies in the cytoplasm.
How are bacterial cells different from plant and animal cells?
They are much smaller and have no nucleus, mitochondria or chloroplasts. The pages on the animal cell and the plant cell show the parts those cells have.