Topics: Immune system, Bacteria, Antibody Pages: 3 (538 words) Published: November 19, 2013
Pathogens are microorganisms that cause diseases like viruses and bacteria. Diseases are caused when Pathogens are transmitted through direct contact. Direct contact involves things such as touching kissing and sexual intercourse. Bacteria

Salmonella bacterium cell
Bacteria come in many shapes and sizes, but even the largest are only 10 micrometres long (10 millionths of a metre). Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill. Viruses

A hepatitis C virus showing DNA enclosed in a protein coat.
Viruses are many times smaller than bacteria. They are among the smallest organisms known and consist of a fragment of genetic material inside a protective protein coat. Viruses can only reproduce inside host cells, and they damage the cell when they do this. A virus can get inside a cell and, once there, take over and make hundreds of thousands of copies of itself. Eventually the virus copies fill the whole host cell and burst it open. The viruses are then passed out in the bloodstream, the airways, or by other routes.

Diseases caused by bacteria include:
food poisoning
whooping cough.
Diseases caused by viruses include:
influenza (flu)
chicken pox

White blood cells can:
ingest pathogens and destroy them
produce antibodies to destroy particular pathogens
produce antitoxins that counteract the toxins released by pathogens.

the pathogens are not the disease - they cause the disease
white blood cells do not eat the pathogens - they ingest them antibodies and antitoxins are not living things - they are specialised proteins

Pathogens contain certain chemicals that are foreign to the body. These chemicals are called antigens. Certain white blood cells, called lymphocytes, can produce specific antibodies to kill a particular pathogen. Antibodies

Antibodies are proteins. They can...
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