Download The_Body_At_War - aiss-science-9

Why Vaccines are good - Vaccines have prevented many diseases
- Diseases are preventable with a vaccine
- Why bring back diseases that have been gone for years?
Why vaccines are bad - Sometimes getting sick is not a bad thing
- Vaccines sometimes decrease the effect of the immune system
- Why put people in danger?
3.2 Little things, Big trouble
Remember
1 Diseases can be divided into two main groups. What are these groups called?
These two groups are infectious and non-infectious.
2 Explain the meaning of `pathogen' and `antigen'.
Pathogen – infectious diseases caused by microbes, they invade the body and stop it working properly.
Antigen – the surface of the pathogen, these are usually made up if protein. These particles can cause
an immune response in the body.
3 Not all bacteria are pathogens. Describe two ways in which bacteria can be useful.
Bacteria can be useful for soil, cheese and wines.
4 Describe two ways in which bacteria can cause disease.
Bacteria can cause disease when they reproduce a substance that is toxic to the surrounding host cells.
Bacteria can also cause disease by stopping the host organism from performing it’s normal activities.
Think
1 Compare the ways that viruses and bacteria reproduce.
Viruses reproduce by making thousands and thousands of copies if themselves.
Bacteria reproduces by dividing into two in a process called binary division.
2 Why is the cell invaded by a virus called a `host' cell?
A cell invaded by a virus is called a host cell because the virus ‘lives’ inside the cell until the cell
cracks open from the masses of virus particles.
3 The skin under the armpits contains over two million bacteria per square centimeter. Why don't they
cause disease more often?
It is good bacteria, these is no way for the bacteria to get into your body.
3.3 Catching worms and more
Remember
1 What is a parasite?
A parasite is an organism that depends on the host for food and shelter. Parasites may be internal or
external.
2 What is a protozoan? List some diseases that are caused by protozoans.
Single celled animal-like organisms are called a protozoan. They are responsible for malaria, amoebic
dysentery and African sleeping sickness.
3 List some human diseases that are caused by fungi.
Some human diseases that are caused by fungi are Athletes foot and thrush.
Think
1 Why is the animal or plant in which a parasite causes disease called a `host'?
The parasite ‘lives’ in the host and depends on the host got shelter and nutrients.
2 (a) Why do you think the disease shown in the photograph below is called ringworm?
Because it is in the shape of a ring.
(b) To what group of living things does it belong?
Parasites
(c) Is it an internal or external parasite?
It is an internal parasite.
Summary – 1st, 2nd and 3rd lines of defense
1st line of defense –
This line prevents the entry of microbes, some of these defenses are physical barriers, such as –
-Skin – Skin protects the organs from damaging chemicals, water and radiation.
-Nasal hairs and Mucus – Air is filtered through the nasal hairs and mucus before entering the lungs.
-Body fluids - Body fluids help flush away particles that may get trapped in the body’s surface, like
saliva and tears. These body fluids contain cleansing properties.
-Acid – Acid produced in the stomach can kill most disease causing microbes before they go further
into the body.
2nd line of defense –
-White blood cells rush to the area affected can fight off the microbes and bacteria.
-The lymphatic system caries pale yellow fluid called lymph.
-The function of the lymphatic system is to remove foreign particles, materials and dead blood cells
before they get into the blood steam.
-Swollen glands are lymph nodes, this is where fluid gets filtered and the foreign particles are trapped.
3rd line of defense –
-Spleen contains cells to capture and destroy foreign particles. If all else fails spleen will go to the
affected area.
-Spleen detects particles in the bloodstream, which they will then destroy.
-Spleen filters blood rather than lymph.