GCSE Biology: Microbes and Disease

The two main causes of disease are bacteria and viruses.


1. Bacteria are 1/100thmm in size.
2. Bacteria are small enough for gas exchange and excretion to be carried out by diffusion.
3. Bacteria can move using their flagella, long whip-like structures.
5. The shape, and sometimes the colour of bacteria can be used to identify them.
6. Bacteria survive poor conditions by forming a thick protective coat around themselves. They are then called spores and can remain dormant for up to 50 years.
7. Bacteria reproduce by splitting in two again and again.


1. Viruses are 1nm (one nano-meter) wide.
2. A virus consists of a string of nuclei and acid surrounded by a hard protein. They can take many shapes and forms.
3. Viruses reproduce by entering a cell and injecting a string of nuclei acid into the cell which in turn multiplies, and many strings are formed. Hard protein shells form around these strings and this forces the cell open, releasing thousands of new viruses which latch onto yet more cells.

Antibody: Substance in the blood which destroys or neutralises antigens. Antobodies latch onto viruses disabling them. Antibodies belong in the gobulin family of proteins.
Antigen: A substance which causes the formation if antibodies. ie: it provokes an immune response. Antigens are usually proteins that are foreign to the body.
Immunity: If a person has a natural resistance to a microbe they can rapidly form large number of antibodies to kill and destroy an infecting microbe. This is called immunity.
Immunisation: Immunisation is artificial immunity, it gives the body a defence to a microbe which it did not previously have a defence to. There are two types of immunisations, vaccine and serum.
Vaccine: A vaccine is a type of immunisation. It involved the body making its own antibodies rather being given some. Modified or killed microbes and sometimes modified toxins are used. These do not harm the body, but makes the body produce antibodies which can stop any microbe trying to infect the body.
Serum: A serum contains antibodies. It has an immediate effect if a person is in an emergency situation. Because the body did not make the antibodies it cannot replicate them so the effect is only temporary.