Unit 20 causes and spread of infection
Bacteria are classified into different groups and can be pathogenic or non-pathogenic. Different types of bacteria are identified by their varying shapes.
Bacteria are simple organisms, made up of just one cell, and are capable of reproducing by themselves. They do this through a process of growing to twice their original size and splitting into two; those two cells then split into two more, and so on. This may appear to be a very simple process; however, conditions have to be right for it to happen and for the bacteria to be viable. Under the right conditions they can divide and multiply rapidly. The term used for this process is binary fission.
Viruses are much smaller than bacteria, and more complex. They can survive out of the body for a time. Viruses are not affected by antibiotics, which is why antibiotics are not prescribed for viral infections. There are, however, antiviral drugs available to treat some infections. Viruses cannot multiply on their own, so they have to invade a ‘host’ cell and take over its machinery in order to be able to make more virus particles. They do this by latching on to human cells and getting inside them. Viruses consist of genetic materials surrounded by a protective coat of protein.
The cells of the mucous membranes, such as those lining the respiratory passages we breathe through, are particularly open to virus attacks because they are not covered by protective skin. As well as all cold and flu infections and most coughs and sore throats, viruses are also the cause of many serious infectious diseases. In order to get rid of a virus, the cell which has been invaded by the virus must be killed, which results in damage to the cells themselves. For this reason, doctors can only control the symptoms of a viral infection, but to date medical research has found no cures.
When a virus invades the body, the immune system releases white blood cells. These cells produce...