Viruses

Question 1

How were viruses discovered

Answer 1

Tobacco plants can suffer from mosaic disease which attacks their leaves causing them to die. In 1900 a scientist carried out an investigation and since the disease was caused by something smaller than a bacteria, the scientist called it a virus

Question 2

Characteristics of viruses

Answer 2

1. Viruses are extremely small - they can only be seen with an electron microscope
2. Have two distinct states: a virus (when active, and a virion (when dormant and not in contact with a host cell)
3. Not living organisms
4. Can only survive inside the cells of living organisms
5. Can only reproduce inside a living cell
6. Viruses can remain in a dormant state
7. Various shapes

Question 3

Different shapes of viruses

Answer 3

1. Polyhedral: has twenty triangular faces
2. Helical: resembles a coiled spring
3. Complex: has a head, sheath and tail fibres

Question 4

Structure of viruses

Answer 4

• viruses are acellular, it is not a cell (has no nucleus, cytoplasm or organelles)
• has a core of DNA or RNA, can’t be both
• nucleic acid is surrounded by a protein coat or capsid
• some can be covered by an envelope of a lipid bilayer