- Viruses are micro-organisms that cannot survive without a
living host. They are always pathogenic (cause disease).
- Viruses are often
called nonliving as they don’t grow feed respire or excrete wastes. They do not have cells and do not have the parts needed to carry out life processes.
- Viruses have a variety of shapes but they all have a protein
case that holds the genetic material.
- Viruses reproduce by entering another
living cell (host) and making copies of themselves inside the host cell. Viruses are always pathogens because the only life process they carry out is reproduction and they must use a host cell to reproduce. Viruses always cause harm or death to the host cell.
Structure of virus:
The common cold is a viral pathogen. People can catch a cold more than once because virus particles mutate often to produce slightly different protein coats. The human immune system does not recognise each mutation of the common cold so the person gets sick again.
