Alive only inside a cell
No metabolic activity whatever happens within a virus. That is because none of the organelles it would need are there.
| Characteristic | Outside a cell | Inside a living host cell |
|---|---|---|
| Cellular organization | No | No |
| Nutrition, respiration, excretion | No | No |
| Reproduction | No | Yes |
A virus can only become active inside a living host cell. Outside one it is as inert as a crystal.
Extra knowledge
The only living characteristic a virus shows is reproduction. When a virus meets a suitable host cell it breaks the host cell membrane and releases the DNA or RNA it contains into that cell. Inside the cell that nucleic acid multiplies and thousands of new viruses are produced. A virus behaves as an organism in this way only inside a living cell.
Figure to be added
One of the eight, and only one
Of the eight characteristics a virus shows exactly one — reproduction. And even that not by itself but by borrowing another organism's cell. A virus is therefore a non-cellular form that cannot be sorted cleanly into living or non-living.