Disease and immunity

Question 1

Define Active immunity

Answer 1

Making antibodies and developing memory cells for future response to infection is known as active immunity
There are two ways in which this active immune response happens:
The body has become infected with a pathogen and so the lymphocytes go through the process of making antibodies specific to that pathogen
Vaccination
Active immunity is slow acting and provides long-lasting immunity

Question 2

Explain the process of lymphocytes and phagocytes

Answer 2

All cells have proteins and other substances projecting from their cell membrane
These are known as antigens and are specific to that type of cell
Lymphocytes have the ability to ‘read’ the antigens on the surfaces of cells and recognise any that are foreign
They then make antibodies which are a complementary shape to the antigens on the surface of the pathogenic cell
The antibodies attach to the antigens and cause agglutination (clumping together)
This means the pathogenic cells cannot move very easily
At the same time, chemicals are released that signal to phagocytes that there are cells present that need to be destroyed

Question 3

Explain Vaccination

Answer 3

Vaccines allow a dead or altered form of the disease-causing pathogen, which contains specific antigens, to be introduced into the body
In this weakened state, the pathogen cannot cause illness but can provoke an immune response
Lymphocytes produce complementary antibodies for the antigens
The antibodies target the antigen and attach themselves to it in order to create memory cells
The memory cells remain in the blood and will quickly respond to the antigen if it is encountered again in an infection by a ‘live’ pathogen
As memory cells have been produced, this immunity is long-lasting

Question 4

Explain Passive Immunity

Answer 4

Passive immunity is a fast-acting, short-term defence against a pathogen by antibodies acquired from another individual
Antibodies pass from mother to infant via breast milk - this is important as it helps the very young to fight off infections until they are older and stronger and their immune system is more responsive
The body does not make its own antibodies or memory cells in passive immunity, hence the name

Question 5

How does chlorea causes diarohea

Answer 5

Bacteria attach to the wall of the small intestine
They produce a toxin
The toxin stimulates the cells lining the intestine to release chloride ions from inside the cells into the lumen of the intestine
The chloride ions accumulate in the lumen of the small intestine and lower the water potential there
Once the water potential is lower than that of the cells lining the intestine, water starts to move out of the cells into the intestine (by osmosis)
Large quantities of water are lost from the body in watery faeces
The blood contains too little chloride ions and water