GCSE Biology 1.1.2 How our bodies defend themselves against infectious diseases

The microorganisms which cause diseases are called PATHOGENS.
Once BACTERIA and VIRUSES get inside your body they REPRODUCE RAPIDLY.

How are pathogens spread?

Defense mechanisms

Painkillers: help to relieve the symptoms of an infectious disease but do not kill the pathogens.
Antibiotics: only work on bacteria by destroying their cell walls (viruses live inside our cells).

Mutation: MRSA - 1000 deaths a year UK
When bacteria reproduce their DNA is made very quickly causing mistakes and mutations that can give them resistance to a certain antibiotic.
The immune system can deal with resistant and non resistant bacteria alike.

Steps to reducing this problem.

Epidemic:
More cases than would normally be expected.
Pandemic:
Much larger/worldwide scale e.g. bird flu.

White blood cells:
Phagocytes: lobed nucleus, ingest/engulf and destroy pathogens.
Lymphocytes: large nucleus, produces antibodies and antitoxins.

Antigens are the chemical on the surface of a pathogen that stimulates an immune response.
Antibodies attach to these ready for the phagocytes to destroy.
Antitoxins counteract the toxins released by the pathogens.

VACCINATIONS = ACQUIRED IMMUNITY.
Made from a dead or inactive form of the disease causing pathogen OR the antigens.
This triggers your natural immune response.

Louis Pasteur, 1850s: It was thought that life originated from non-living forms of matter - SPONTANEOUS GENERATION.
'Swan-necked flask' with sterile broth, bacteria was trapped in the bend, neck was broken and bacteria got in.

Alexander Fleming accidentally discovered a fungus (penicillium) growing on an old bacterial plate which had killed all the bacteria around it.
The first antibiotic - penicillin.

Agar Plates and Aseptic Techniques:
Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.
Wash hands & swab bench with disinfectant.
Heat inoculating loop & neck of bottle to sterilize.
Open lid of agar plate slightly & for a short amount of time - reduce air contamination.