Eukaryotes and prokaryotes (AQA GCSE Biology): Revision Notes
Eukaryotes and prokaryotes
What are eukaryotes and prokaryotes?
All living things are made of cells, but there are two main types of cells that work very differently.
Eukaryotic cells are found in animals and plants. These cells have a proper nucleus that controls the cell.
Prokaryotic cells are found in bacteria. These cells do not have a nucleus - their genetic material floats freely inside the cell.
The presence or absence of a nucleus is the key difference that separates all life forms into these two major groups.
Similarities between all cells
Despite their differences, both eukaryotic and prokaryotic cells share some fundamental features that are essential for life:
Both eukaryotic and prokaryotic cells share some basic features:
- Cell membrane - controls what goes in and out of the cell
- Cytoplasm - jelly-like substance where chemical reactions happen
These shared features show that all life forms have common basic requirements for survival.
Bacterial cells (prokaryotes)
Bacterial cells are prokaryotic, which means they have a fundamentally different structure from animal and plant cells. Understanding their unique features helps explain how bacteria can survive and reproduce successfully.
Key features of bacterial cells
Cell wall - Bacteria have a protective cell wall around them, but it's made of different materials compared to plant cell walls.
No nucleus - The most important difference is that bacterial cells do not have a nucleus. Instead, they have a single loop of DNA that floats freely in the cytoplasm.
Chromosomal DNA - This single loop contains most of the bacterial genes and controls how the bacterium works.
Ribosomes - These are tiny structures that make proteins. They're much smaller than the ribosomes found in animal and plant cells.
Extra features some bacteria have
Flagellum - Some bacteria have a whip-like tail called a flagellum that helps them move around.
Plasmids - Some bacteria contain small circles of extra DNA called plasmids. These carry additional genes that aren't found in the main chromosomal DNA.
Plasmids are particularly important in biotechnology and medicine because they can be used to transfer genes between bacteria, and they often carry genes for antibiotic resistance.
Main differences summary
| Feature | Eukaryotic cells | Prokaryotic cells |
|---|---|---|
| Nucleus | Yes - contains DNA | No - DNA floats freely |
| Examples | Animal and plant cells | Bacterial cells |
| Size | Generally larger | Generally smaller |
| DNA location | Inside nucleus | Free in cytoplasm |
| Plasmids | No | Sometimes present |
Key Points to Remember:
- Animal and plant cells are eukaryotic - they have a nucleus
- Bacterial cells are prokaryotic - they have no nucleus
- All cells have a cell membrane and cytoplasm
- Bacterial DNA floats freely in the cytoplasm as a single loop
- Some bacteria can move using a flagellum
- Plasmids give bacteria extra genes that help them survive