Bacterium are cells that are 1% in size of a normal body cell. They make us ill by doing 2 things producing toxins and damging our cells.
Viruses are not cells they are 1% in size of a normal bacterium cell. They replicate themselves by invading our cells they use our cells machinery to produce copies of themselves.The cell will usually burst releasing the new viruses. The cell damge is what makes us ill
Your skin, hair, mucus and respiratory tract (breathing tract) have ways from preventing micro-organisms from getting into your body. And through wounds platlets help blood clot quickly and seal wounds. For e.g. blood with a low number of platlets will clot more slowly. But if a pathogen (a harmul micro organism that causes a disease) eneds up getting into your body.Your immune system kicks in by producing white blood cells, when they come across a pathogen there are 2 main lines of attck.
1) Engulf and digest - White blood cells engulf and digest invadign mico-organism.
2) Producing antibodies - Every invading cell has a unique molecule on it's surface called an antigen. When your white blood cell comes across a foreign antigen (i.e one it doesnt recognize) it produces a specifc protein called antibodies which lock on and kill it, antibodies is specific to that anitgen so it wont lock on to any others. When you get the same disease again your white blood cells are able to produce antibodiesto kill the pathogen so you dont get it, you are then naturaly immune to the disease.
3)Producing Antioxins - White blood cells produce antitoxins to conteract toxins produced by invading bacteria.
When you get infected with a new micro-organism your body takes a few days to learn how to deal with it. By that time you can become pretty ill.Vaccination involves injecting small amuounts of dead or innactive pathogens, which carry antigens on it's surface this causes your white blood cells to produce antibodies to attck them - even though it's harmless (dead and innactive). For e.eg MMR vaccine contains the weakened versions of three viruses measles, mumps…