Page 24 - 01. Classification of living things - Biology Notes IGCSE
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#9: Viruses
Viruses are not true living things. They are not considered to be alive,
because on their own they can do nothing until they enter a living cell.
Viruses are complicated assemblies of molecules including proteins, nucleic
acids, lipids, carbohydrates…
When viruses encounter a cell, they take over cell’s machinery. A series of
chemical reactions occur that lead to the production of new viruses. Theses
new viruses burst out of the cell and invade others, where the process is
repeated. The host cell is usually killed when this happens.
These steps are completely passive, that is, they are predefined by the
nature of the molecules that comprise the virus particle. Viruses don’t
actually ‘do’ anything. Without cells, viruses would not be able to
multiply.
