What a virus is

Some living forms are hard to identify as either living or non-living objects. The example is the virus.

Figure to be added

Figure 8.16 — the structure of a virus as modelled from the electron microscope: the protein coat, the DNA, the tail and the tail fibres.

Point	The virus
Size	About a thousandth of a bacterium
Observation	Only with an electron microscope
Made of	A nucleic acid with a protein coat around it
The nucleic acid	DNA or RNA
Is it a cell?	No — viruses are not counted as cells

What "not a cell" means here

Recall that the first characteristic in this chapter was cellular organization. A virus has no plasma membrane, no cytoplasm and no organelles. So it fails the very first of the eight.

Viruses of many shapes and sizes have been identified. They show living and non-living characteristics according to the situation they are in — and what "the situation" means is what the next page explains.