1.4 Pathogens

Understand that a pathogen causes disease and may be a fungus, bacterium, protoctist or virus.
Viruses are non-living particles smaller than bacteria. They are parasites that reproduce only inside living cells and can infect every type of organism. They have no cellular structure, but have a protein coat and contain either DNA or RNA. Examples include tobacco mosaic virus, which prevents chloroplast formation and discolours tobacco leaves; influenza virus; and HIV, which causes AIDS.