CIE A Level Biology (9700) 2019-2021

Revision Notes

1.2.5 Viruses

Key Features of Viruses

  • Viruses are non-cellular infectious particles that straddle the boundary between ‘living’ and ‘non-living’
  • They are relatively simple in structure; much smaller than prokaryotic cells (with diameters between 20 and 300 nm)
  • Structurally they have:
    • A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
    • A protein coat called a ‘capsid’
  • Some viruses have an outer layer called an envelope formed usually from the membrane-phospholipids of a cell they were made in
  • All viruses are parasitic in that they can only reproduce by infecting living cells and using their protein-building machinery (ribosomes) to produce new viral particles

Cell Components- Virus, downloadable AS & A Level Biology revision notes

Viruses are not cellular like prokaryotes and eukaryotes – this is just one example of a virus structure

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top