it is because virus does not have a cell machinery to divide itself. when it comes to affect our body's tissue, it uses the blood cell's machinery to divide and infect other blood cell.
The metabolic machinery of the cell is located in the mitochondria.
cell body
viruses behave like dead particles out of the cell and in specific out its particular cell. Once inside its cell, the virus uses the cell's machinery to "come alive" it then begins to reproduce and infect other of the same type of cell.
ATP
Some of the machinery that is exported by the Netherlands includes printers, telephones, and digital cameras. Also exported are computers and cell phones.
virus.
adenosine triphoshate
a host cell so that the virus is able to use the host's cell machinery to replicate
Machinery
a virus
the vocabulary is cellular metabolism(anbolism and catabolism).