The document discusses the immune system and how it protects the body from pathogens and foreign proteins. It describes how antigens on pathogens stimulate white blood cells to produce antibodies to disable the pathogen, and phagocytes then engulf and digest the pathogens. It also discusses artificial immunity through vaccines, how vaccines use weakened pathogens to produce immunity without causing disease, and how vaccines work by stimulating antibody production. Finally, it briefly mentions some common diseases caused by pathogens like tuberculosis, cholera, and typhoid.

1. BIOLOGY
GRADE - 9

2. MICROORGANISMS
AND
DISEASE
UNIT - 4

4. The immune system
• Immune system the system in the body which protects the body
against invading microorganisms and foreign proteins.
• Like all living cells, pathogens carry unique protein molecules called
antigens on their cell surfaces.
• When a pathogen gets into the body the antigens on the surface
stimulate a response by the immune system.

5. The immune system
• White blood cells (lymphocytes) produce antibodies to disable the
pathogen.
• Other white blood cells (the phagocytes) then engulf and digest the
disabled pathogens.
• Once someone have had a disease, the immune system ‘remembers’
the antigen and the right antibody to deal with it.

6. Artificial immunity
• Our body has its own natural ability to protect itself against artificial disease,
however if the immune
• system of the body fails to defend some dangerous disease it will be treated
by artificial immunity.
• Artificial immunity is given in the form of vaccine/drugs.
• Artificial active immunity: involves introduction of weakened or dead
pathogen in the body which stimulates the body to produce its own
antibodies.

7. Artificial immunity
• It can be natural from mother to child (natural passive)until the child
produces its own natural active immunity
• It has long-lasting effect on the body
• Artificial passive immunity: it involves giving specific antibodies in the form
of infection
• It provides a high type of resistance but last only for short time.

8. Vaccination (immunization) :
• is the use of dead or weakened strains of pathogens to produce immunity to
dangerous diseases
• the vaccination work through the following ways
• a weak or dead form of the infecting organism is put into the body by injection or
by mouth
• once in the body, the white blood cells respond by producing antibodies
• If the living micro-organism enters the body in the future, antibodies are produced
very rapidly to destroy it and so the disease does not develop

9. 4.2 Diseases
• Disease is any form of disorder in or on the body distorts it’s normal
functioning
• Some of the most commonly known diseases which are caused by
pathogenic organisms among them include: tuberculosis, AWD, cholera
andtyphoid, cholera, typhoidandgastroenteritis

10. Figure 4.12
The head of a
tapeworm is
well adapted
for holding on
to the lining
of your gut

11. Disease….

12. Figure 4.13
Tapeworms can
grow up to 5
meters in length
It’s amazing that
a worm this long
can live in your
gut!