6-2 The Immune System

The human body has a defense system called the immune system which resists diseases.  White blood cells and antibodies rid the body of germs, which scientists call microbes.  Microbes are very small organisms that can be seen only under a microscope.  Bacteria, protozoa, viruses and fungi are microbes.  White blood cells attack the foreign microbes that appear in the blood.  They actually surround the intruders and digest them.

Antibodies work in a different way.  They are not actual cells, but special molecules of protein.  They have the special ability to attach themselves to specific foreign proteins that are found in microbes.   These foreign proteins are called antigens.  Antibodies deactivate the antigen so it is unable to cause harm.  Some of the antibodies remain in the bloodstream and if the invading microbe appears in the future it is attacked again.   This protection is call immunity.  An example of an immunity is chicken pox.  If an individual has had the chicken pox they will not get it again.  Why?  The body has build up a lifetime immunity to this disease.  However diseases like the flu occur again and again.  The reason for this is because the viruses that cause it are constantly changing the shape of the antigens.  Therefore new antibodies have to be created to fight them off.  The body remains sick until the body creates enough new antibodies and makes enough white and red blood cells to destroy the virus.

Directions: Answer the questions about the immune system.

The immune system is a system of the human body which resists diseases.

Scientists call the very small organisms that can be seen only under a microscope .

blood cells attack and surround the intruders and digest them.

are special molecules of protein that have the special ability to attach themselves to specific foreign proteins that are found in microbes.

The foreign proteins found in microbes are called .

 A protection called occurs when antibodies remain in the bloodstream and attack invading microbes that appears in the future.

Which of the following will the body build an immunity to?

flu

cold

chicken pox

Which of the following will the body not build an immunity to?

flu

chicken pox

Bacteria, protozoa, viruses and fungi are

flu symptoms

microbes

antigens