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
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
cells attack and surround the intruders and digest them.
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?
Which of the following will the body not build an immunity to?
protozoa, viruses and fungi are
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