Viruses attack living cells like soldiers taking over a factory.
The processes a plant relies on to survive, like growth, metabolism and photosynthesis, take place in cells.
Viruses can subvert the cells’ functions to their own ends, eventually killing the tissues that the cells make up.
First, the virus attaches itself to the external wall of a cell, eats a hole through the wall and injects its genetic material into the cell.
Then the viral genetic material directs the host cell to stop whatever it is doing and start making viral genetic material.
When several hundreds of thousands of viral particles, or fragments of genetic material, have been produced, they coat themselves with a protein and produce an enzyme that digests the cell from inside out.
As the cell is destroyed it releases all the thousands of viruses, which go to other cells and do the same thing.