Chapter Note: Diseases and Immunity | Biology for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Pathogens and immunity
? A microorganisms is a tiny organism that can only be seen with a microscope
? A pathogen is a microorganism that causes disease.
Group to which pathogen belongs Examples of diseases which they cause
Viruses Influenza. Common cold, poliomyelitis, AIDS
Bacteria Cholera, syphilis, whooping cough, tuberculosis
tetanus
Protoctists Malaria, amoebic dysentery
Fungi Athlete’s foot, ringworm
? Diseases that are caused by pathogens can usually be passed from one person to another. They are
called transmissible diseases
How pathogens enter the body
? Direct contact
? The passing of a pathogen to an uninfected person is called transmission
? The entry of the pathogen into the body is known as infection. The person which pathogen lives
and breeds is said to be a host
? Viruses can be transmitted when an infected persons blood comes into contact with another
person's blood
? The fungus that causes skin infection can be shared by sharing the came towel with an infected
person.
? Indirect transmission
? Through the respiratory passage
¦ Cold and influenza viruses are carried in the air in tiny droplets of moisture. Every time
someone with these illnesses speaks or coughs, millions of viruses are propelled into the
air.
¦ If you breathe these droplets you may be infected as well. You can also pick up viruses if
you touch a surface on which they are present and put your hands on your face.
? In food or water
¦ Bacteria such as Salmonella can enter your alimentary canal with the food that you eat.
If you eat a large number of these bacteria, you may get food poisoning
¦ Fresh foods such as fruit and vegetables should be washed in clean water before you
eat them. Cooking usually destroys bacteria so eating recently cooked food is generally
safe.
¦ Many pathogens including viruses that cause poliomyelitis and the bacterium that
causes cholera are transmitted in water. If you swim i n water that contains these
pathogens or drink water containing them you run the risk of catching these diseases.
? By vectors
¦ A vector is an organism that carries a pathogen from one host to another. Sogs, skunks,
raccoons and bats are vectors for rabies protoctista pathogen Plasmodium in their saliva
Page 2


Pathogens and immunity
? A microorganisms is a tiny organism that can only be seen with a microscope
? A pathogen is a microorganism that causes disease.
Group to which pathogen belongs Examples of diseases which they cause
Viruses Influenza. Common cold, poliomyelitis, AIDS
Bacteria Cholera, syphilis, whooping cough, tuberculosis
tetanus
Protoctists Malaria, amoebic dysentery
Fungi Athlete’s foot, ringworm
? Diseases that are caused by pathogens can usually be passed from one person to another. They are
called transmissible diseases
How pathogens enter the body
? Direct contact
? The passing of a pathogen to an uninfected person is called transmission
? The entry of the pathogen into the body is known as infection. The person which pathogen lives
and breeds is said to be a host
? Viruses can be transmitted when an infected persons blood comes into contact with another
person's blood
? The fungus that causes skin infection can be shared by sharing the came towel with an infected
person.
? Indirect transmission
? Through the respiratory passage
¦ Cold and influenza viruses are carried in the air in tiny droplets of moisture. Every time
someone with these illnesses speaks or coughs, millions of viruses are propelled into the
air.
¦ If you breathe these droplets you may be infected as well. You can also pick up viruses if
you touch a surface on which they are present and put your hands on your face.
? In food or water
¦ Bacteria such as Salmonella can enter your alimentary canal with the food that you eat.
If you eat a large number of these bacteria, you may get food poisoning
¦ Fresh foods such as fruit and vegetables should be washed in clean water before you
eat them. Cooking usually destroys bacteria so eating recently cooked food is generally
safe.
¦ Many pathogens including viruses that cause poliomyelitis and the bacterium that
causes cholera are transmitted in water. If you swim i n water that contains these
pathogens or drink water containing them you run the risk of catching these diseases.
? By vectors
¦ A vector is an organism that carries a pathogen from one host to another. Sogs, skunks,
raccoons and bats are vectors for rabies protoctista pathogen Plasmodium in their saliva
Body defences
? Mechanical barriers
? Mechanical barriers act as a physical obstruction in order to prevent pathogens from entering
our body. For example
¦ Skin
¦ Nose hairs
? Chemical barriers
? Chemical barriers are chemical substances in the body which help to trap or destroy pathogens.
For example
¦ Mucus
? Traps bacteria that enters the respiratory system via air. The mucus is then beat
upwards by the cilia and pushed up to the mouth
¦ Stomach acid
? The acidity kills pathogens that enter our digestive system via the food we eat.
? Food hygiene
? Keep your own bacteria and viruses away from food. Always wash your hands before touching
or eating food.
? Keep animals away from food. Animals are more likely to have harmful bacteria on them. Some
particularly dangerous things such as house flies have harmful bacteria on their feet. Rats or
mice often carry pathogens. Covering food to keep flies and other animals is always a good idea
? Do not keep foods at room temperature for long periods of time. Bacteria reproduction and
temperature are directly proportional therefore higher the temperature, higher reproduction of
the bacteria therefore it should be kept in the fridge after a short period of time
? Keep raw meat away from other foods. Raw meat often contains bacteria. If the bacteria get into
other foods that might be eaten raw, then they might breed there. Therefore foods such as
salads and vegetables that are to be eaten raw should be washed in clear water before eating.
? Waste disposal
? All rubbish from countries is usually dumped into a landsite, all kinds of rubbish are just piled up.
Animals such as houseflies, rats and stray dogs forage for food in the rubbish
? Bacteria breed in the waste food. Dangerous chemicals seep out of the rubbish polluting the
ground and waterways.
? Some of the rubbish in the landfill site is rotted by decomposers, especially bacteria. This
produces a gas called methane which can cause explosions if it's allowed to build up.
? Placing pipes in the rubbish can allow the methane to escape harmlessly into the air or it can be
collected as fuel
? Sewage treatment
? Sewage is waste liquid that has come from houses , industry and other parts of villages.
Sewage is mostly water, but also contains many other substances, these include urine and
faeces, toilet paper, detergents, oil and many other chemicals.
? Raw sewage contains many bacteria and other microorganisms, some of which are likely to be
pathogens especially if it gets into their mouths.
? Poliomyelitis and cholera are just 2 of the serious diseases that can be transmitted through
water polluted with raw sewage.
Page 3


Pathogens and immunity
? A microorganisms is a tiny organism that can only be seen with a microscope
? A pathogen is a microorganism that causes disease.
Group to which pathogen belongs Examples of diseases which they cause
Viruses Influenza. Common cold, poliomyelitis, AIDS
Bacteria Cholera, syphilis, whooping cough, tuberculosis
tetanus
Protoctists Malaria, amoebic dysentery
Fungi Athlete’s foot, ringworm
? Diseases that are caused by pathogens can usually be passed from one person to another. They are
called transmissible diseases
How pathogens enter the body
? Direct contact
? The passing of a pathogen to an uninfected person is called transmission
? The entry of the pathogen into the body is known as infection. The person which pathogen lives
and breeds is said to be a host
? Viruses can be transmitted when an infected persons blood comes into contact with another
person's blood
? The fungus that causes skin infection can be shared by sharing the came towel with an infected
person.
? Indirect transmission
? Through the respiratory passage
¦ Cold and influenza viruses are carried in the air in tiny droplets of moisture. Every time
someone with these illnesses speaks or coughs, millions of viruses are propelled into the
air.
¦ If you breathe these droplets you may be infected as well. You can also pick up viruses if
you touch a surface on which they are present and put your hands on your face.
? In food or water
¦ Bacteria such as Salmonella can enter your alimentary canal with the food that you eat.
If you eat a large number of these bacteria, you may get food poisoning
¦ Fresh foods such as fruit and vegetables should be washed in clean water before you
eat them. Cooking usually destroys bacteria so eating recently cooked food is generally
safe.
¦ Many pathogens including viruses that cause poliomyelitis and the bacterium that
causes cholera are transmitted in water. If you swim i n water that contains these
pathogens or drink water containing them you run the risk of catching these diseases.
? By vectors
¦ A vector is an organism that carries a pathogen from one host to another. Sogs, skunks,
raccoons and bats are vectors for rabies protoctista pathogen Plasmodium in their saliva
Body defences
? Mechanical barriers
? Mechanical barriers act as a physical obstruction in order to prevent pathogens from entering
our body. For example
¦ Skin
¦ Nose hairs
? Chemical barriers
? Chemical barriers are chemical substances in the body which help to trap or destroy pathogens.
For example
¦ Mucus
? Traps bacteria that enters the respiratory system via air. The mucus is then beat
upwards by the cilia and pushed up to the mouth
¦ Stomach acid
? The acidity kills pathogens that enter our digestive system via the food we eat.
? Food hygiene
? Keep your own bacteria and viruses away from food. Always wash your hands before touching
or eating food.
? Keep animals away from food. Animals are more likely to have harmful bacteria on them. Some
particularly dangerous things such as house flies have harmful bacteria on their feet. Rats or
mice often carry pathogens. Covering food to keep flies and other animals is always a good idea
? Do not keep foods at room temperature for long periods of time. Bacteria reproduction and
temperature are directly proportional therefore higher the temperature, higher reproduction of
the bacteria therefore it should be kept in the fridge after a short period of time
? Keep raw meat away from other foods. Raw meat often contains bacteria. If the bacteria get into
other foods that might be eaten raw, then they might breed there. Therefore foods such as
salads and vegetables that are to be eaten raw should be washed in clear water before eating.
? Waste disposal
? All rubbish from countries is usually dumped into a landsite, all kinds of rubbish are just piled up.
Animals such as houseflies, rats and stray dogs forage for food in the rubbish
? Bacteria breed in the waste food. Dangerous chemicals seep out of the rubbish polluting the
ground and waterways.
? Some of the rubbish in the landfill site is rotted by decomposers, especially bacteria. This
produces a gas called methane which can cause explosions if it's allowed to build up.
? Placing pipes in the rubbish can allow the methane to escape harmlessly into the air or it can be
collected as fuel
? Sewage treatment
? Sewage is waste liquid that has come from houses , industry and other parts of villages.
Sewage is mostly water, but also contains many other substances, these include urine and
faeces, toilet paper, detergents, oil and many other chemicals.
? Raw sewage contains many bacteria and other microorganisms, some of which are likely to be
pathogens especially if it gets into their mouths.
? Poliomyelitis and cholera are just 2 of the serious diseases that can be transmitted through
water polluted with raw sewage.
The immune system
? There is one type of white blood cell called lymphocytes which produce chemicals called antibodies.
These chemicals help to destroy pathogens
? Antibodies
? There are thousands of different kinds of
lymphocytes. Each kind is able to produce a
different sort of antibody
? An antibody is a protein molecule with a
particular shape. Like an enzyme molecule, its
shape is just right to fit into another molecule.
? To destroy a particular pathogen, antibody
molecules must be made which are just the right
shape to fit into molecules on the outside of the
pathogen. These pathogen molecules are called
antigens.
? When antibody molecules lock onto the
pathogen, they kill the pathogen. One way is
simple to alert phagocytes to the presence of
pathogens, so that they come and destroy them.
Another way is that the antibodies may start off a
series of reactions in the blood which produce
enzymes to digest the pathogens.
? Most of the time, most of the lymphocytes do not
produce antibodies. It would be a waste of
energy and materials if they did. Instead, each lymphocyte waits for a signal that is a pathogen
which can be destroyed by its particular antibody.
? If the pathogen enters the body, it's likely to meet a large number of lymphocytes. The
lymphocyte will start to divide rapidly by mitosis, making a clone of lymphocytes just like itself.
These lymphocytes that secrete their antibody, destroying the pathogen
? Memory cells
? When a lymphocyte clones itself, not all of the cells
make antibodies. Some of them simply remain in the
blood and other parts of the body, these are call
? If the same kind of pathogen gets into the body again,
these memory cells will be ready and waiting for
them. They will kill the pathogens before they have
time to produce a larger population and do any harm.
The person has become immune to that type of
pathogen.
? Vaccination
? A vaccine contains weakened or dead viruses or
bacteria that normally cause diseases. These
pathogens have the same antigens as the normal
ones but they are not able to cause fatal diseases
Page 4


Pathogens and immunity
? A microorganisms is a tiny organism that can only be seen with a microscope
? A pathogen is a microorganism that causes disease.
Group to which pathogen belongs Examples of diseases which they cause
Viruses Influenza. Common cold, poliomyelitis, AIDS
Bacteria Cholera, syphilis, whooping cough, tuberculosis
tetanus
Protoctists Malaria, amoebic dysentery
Fungi Athlete’s foot, ringworm
? Diseases that are caused by pathogens can usually be passed from one person to another. They are
called transmissible diseases
How pathogens enter the body
? Direct contact
? The passing of a pathogen to an uninfected person is called transmission
? The entry of the pathogen into the body is known as infection. The person which pathogen lives
and breeds is said to be a host
? Viruses can be transmitted when an infected persons blood comes into contact with another
person's blood
? The fungus that causes skin infection can be shared by sharing the came towel with an infected
person.
? Indirect transmission
? Through the respiratory passage
¦ Cold and influenza viruses are carried in the air in tiny droplets of moisture. Every time
someone with these illnesses speaks or coughs, millions of viruses are propelled into the
air.
¦ If you breathe these droplets you may be infected as well. You can also pick up viruses if
you touch a surface on which they are present and put your hands on your face.
? In food or water
¦ Bacteria such as Salmonella can enter your alimentary canal with the food that you eat.
If you eat a large number of these bacteria, you may get food poisoning
¦ Fresh foods such as fruit and vegetables should be washed in clean water before you
eat them. Cooking usually destroys bacteria so eating recently cooked food is generally
safe.
¦ Many pathogens including viruses that cause poliomyelitis and the bacterium that
causes cholera are transmitted in water. If you swim i n water that contains these
pathogens or drink water containing them you run the risk of catching these diseases.
? By vectors
¦ A vector is an organism that carries a pathogen from one host to another. Sogs, skunks,
raccoons and bats are vectors for rabies protoctista pathogen Plasmodium in their saliva
Body defences
? Mechanical barriers
? Mechanical barriers act as a physical obstruction in order to prevent pathogens from entering
our body. For example
¦ Skin
¦ Nose hairs
? Chemical barriers
? Chemical barriers are chemical substances in the body which help to trap or destroy pathogens.
For example
¦ Mucus
? Traps bacteria that enters the respiratory system via air. The mucus is then beat
upwards by the cilia and pushed up to the mouth
¦ Stomach acid
? The acidity kills pathogens that enter our digestive system via the food we eat.
? Food hygiene
? Keep your own bacteria and viruses away from food. Always wash your hands before touching
or eating food.
? Keep animals away from food. Animals are more likely to have harmful bacteria on them. Some
particularly dangerous things such as house flies have harmful bacteria on their feet. Rats or
mice often carry pathogens. Covering food to keep flies and other animals is always a good idea
? Do not keep foods at room temperature for long periods of time. Bacteria reproduction and
temperature are directly proportional therefore higher the temperature, higher reproduction of
the bacteria therefore it should be kept in the fridge after a short period of time
? Keep raw meat away from other foods. Raw meat often contains bacteria. If the bacteria get into
other foods that might be eaten raw, then they might breed there. Therefore foods such as
salads and vegetables that are to be eaten raw should be washed in clear water before eating.
? Waste disposal
? All rubbish from countries is usually dumped into a landsite, all kinds of rubbish are just piled up.
Animals such as houseflies, rats and stray dogs forage for food in the rubbish
? Bacteria breed in the waste food. Dangerous chemicals seep out of the rubbish polluting the
ground and waterways.
? Some of the rubbish in the landfill site is rotted by decomposers, especially bacteria. This
produces a gas called methane which can cause explosions if it's allowed to build up.
? Placing pipes in the rubbish can allow the methane to escape harmlessly into the air or it can be
collected as fuel
? Sewage treatment
? Sewage is waste liquid that has come from houses , industry and other parts of villages.
Sewage is mostly water, but also contains many other substances, these include urine and
faeces, toilet paper, detergents, oil and many other chemicals.
? Raw sewage contains many bacteria and other microorganisms, some of which are likely to be
pathogens especially if it gets into their mouths.
? Poliomyelitis and cholera are just 2 of the serious diseases that can be transmitted through
water polluted with raw sewage.
The immune system
? There is one type of white blood cell called lymphocytes which produce chemicals called antibodies.
These chemicals help to destroy pathogens
? Antibodies
? There are thousands of different kinds of
lymphocytes. Each kind is able to produce a
different sort of antibody
? An antibody is a protein molecule with a
particular shape. Like an enzyme molecule, its
shape is just right to fit into another molecule.
? To destroy a particular pathogen, antibody
molecules must be made which are just the right
shape to fit into molecules on the outside of the
pathogen. These pathogen molecules are called
antigens.
? When antibody molecules lock onto the
pathogen, they kill the pathogen. One way is
simple to alert phagocytes to the presence of
pathogens, so that they come and destroy them.
Another way is that the antibodies may start off a
series of reactions in the blood which produce
enzymes to digest the pathogens.
? Most of the time, most of the lymphocytes do not
produce antibodies. It would be a waste of
energy and materials if they did. Instead, each lymphocyte waits for a signal that is a pathogen
which can be destroyed by its particular antibody.
? If the pathogen enters the body, it's likely to meet a large number of lymphocytes. The
lymphocyte will start to divide rapidly by mitosis, making a clone of lymphocytes just like itself.
These lymphocytes that secrete their antibody, destroying the pathogen
? Memory cells
? When a lymphocyte clones itself, not all of the cells
make antibodies. Some of them simply remain in the
blood and other parts of the body, these are call
? If the same kind of pathogen gets into the body again,
these memory cells will be ready and waiting for
them. They will kill the pathogens before they have
time to produce a larger population and do any harm.
The person has become immune to that type of
pathogen.
? Vaccination
? A vaccine contains weakened or dead viruses or
bacteria that normally cause diseases. These
pathogens have the same antigens as the normal
ones but they are not able to cause fatal diseases
? When the pathogens are introduced into the body, they are recognised by the lymphocytes that
can make memory cells, which give long term immunity.
? Active immunity
? Defence against a pathogen by antibody production in the body. A person has active immunity
to a disease if they have made their own antibodies and memory cells that protect against it
? You can develop active immunity by
¦ Having the disease and getting over it
¦ Being vaccinated with weakened pathogens
? Active immunity can be very long-lasting.
? Passive immunity
? Short-term defence against a pathogen by antibodies acquired from another individual such as
from mother to infant.
? Babies get passive immunity by breastfeeding. Breast milk contains antibodies from the mother
which are passed on to her baby. This is useful as a young baby’s immune system is not well
developed, and so the mother’s antibodies protect it against any diseases to which she is
immune.
? Another way is to be injected with antibodies that have been made by another organism
? Passive immunity only lasts for a short time as the antibodies eventually break down. No
lymphocytes have been stimulated to make clones of themselves so no production of memory
cells.
? Auto-immune diseases
? Lymphocytes behave as though some of our own cells are foreign and react to them as they
would to an invasion of pathogens
? Diseases that result from this kind of malfunction of the immune system are called auto-imune
diseases. For example Type 1 diabetes
? Type 1 diabetes
? One of the hormones produced by pancreas with insulin, this hormone is made when blood
glucose concentration rises above normal, it causes the concentration to fall
? Insulin is made by a particular type of cell in the pancreas called beta cells
? In some people, the cells of the immune system attack the beta cells and destroy them. The
loss of beta cells means that insulin is no longer produced so blood glucose concentration is not
controlled.
? This results in diabetes in which blood glucose levels fluctuate widely.
? Most people with type 1 diabetes take insulin at regular intervals as well as taking great care
over what they eat.