A-LEVEL BIOLOGY AQA NOTES
structure of prokaryotic cells & viruses
Prokaryotic Cells
- Prokaryotes are smaller and simpler than eukaryotes
Feature |
Eukaryotic Cell |
Prokaryotic Cell |
Nucleus |
Present |
Absent |
DNA |
Linear and packaged into chromosomes in nucleus |
Circular and freely floating in cytoplasm |
Cell Membrane |
Present |
Present |
Membrane-bound Organelles |
Present |
Absent |
Ribosomes |
Present (80S) |
Present (70S) |
Cell Wall |
Sometimes (Celloulose or chitin) |
Present (peptidoglycan) |
Chloroplasts |
Sometimes |
Absent |
Flagellum |
Absent |
Sometimes |
Capsule |
Absent |
Sometimes |
Plasmid |
Absent |
Sometimes |
- Bacteria replicate by binary fission
Viruses
- Viruses are acellular and non-living.
- The basic structure of viruses is:
- Viruses replicate by binding to the host cell, injecting their genetic material into the cell, using the host’s machinery to replicate & burst out of the host cell.
