Immunology

Question 1

What is a disease?

Answer 1

A condition that impairs the normal functioning of the body

A disorder with specific cause and recognisable signs and symptoms

Question 2

What is a communicable disease?

Answer 2

Disease caused by pathogens (disease causing organisms) and are transmitted from one host organism to another (infectious)

Question 3

What is a non-communicable disease?

Answer 3

Not caused by pathogens, they can be inherited, deficiency diseases, caused by lifestyle

Question 4

List some viral pathogens

Answer 4

Rhinovirus
HIV
Herpesvirus 
Lyssavirus 
Influenza virus 
Hepatitis Viruses 
Filovirus

Question 5

Key points about viruses

Answer 5

Are non- cellular. They are not generally classed as living organisms
Have a typical size range of 20-300nm
Contain no cytoplasm or nucleus or organell s
Covered in a protein coat
Are parasitic, and depend on a host cell for both their metabolism and their reproduction

Question 6

Key points about fungi

Answer 6

Rarely found as discrete cells
Have a nucleus and membrane bound organelles. So are called eukaryotic cells
Are plant like in appearance but lack chlorophyll
Have rigid cell walls made of chitin

Question 7

List some diseases cause by fungi?

Answer 7

Ring worm
Athletes foot
Black Sigatoka

Question 8

List some diseases caused by protoctista

Answer 8

Malaria
Tomato late blight
Potato late blight

Question 9

What is direct transmission?

Answer 9

The pathogen is transferred directly from one host individual to another by direct contact e.g HIV
Coughing and sneezing can produce droplets containing pathogens which spread directly to someone else e.g influenza, tuberculosis

Question 10

In direct transmission in animals

Answer 10

Via an intermediary or secondary host, such as a vector that transmits the pathogen in its own body E.g the vector Mosquitoes transmit the pathogen plasmodium that causes malaria

Question 11

Explain who plants defend against initial attack

Answer 11

Callose is synthesised and deposited between cell walls in the cell next to the infected cell
In plasmodesmata between infected cells and their neighbours preventing pathogens entering
In sieve plates in the plasmodesmata sealing off the infected part and preventing spread of pathogens

Question 12

Non specific immune response

Answer 12

1.skin
Physical barrier to prevent entry of microorganisms and secrete fatty acids to lower pH
2. Mucous membranes /goblet cells
Produce mucus which traps pathogens
Cilia
Remove pathogens/parasite
3. Expulsive reflexes
Coughing and sneezing forces mucus/ pathogens out of the nasal passages and mouth
4. Lysozyme
Enzyme in blood sweat and tears breaks down bacterial cell walls
Nasal secretions contain antibacterial chemical and ear wax traps pathogens and contains an antibacterial chemical

Question 13

Second line of defence

Answer 13

If the skin has been penetrated and pathogens May have entered the body then there is a second line of defence 
Blood clotting 
Inflammation
Wound repair 
Phagocytosis

Question 14

Describe blood clotting

Answer 14

A blood clot is a mesh of protein (fibrin) fibres. Blood clots plug wounds to prevent pathogen entry and blood loss. They’re formed by a series of chemical reactions that take place when platelets

Question 15

Describe inflammation

Answer 15

The signs of inflammation include swelling, pain, heat and redness. It can be triggered by tissue damage, the damaged tissue released molecules which increases the permeability of the blood vessels, so they start to leak fluid into the surrounding area. This causes swelling and helps to isolate any pathogens that may have entered the damaged tissue. The molecules also cause vasodilation (widening of the blood vessels), which makes the area hot brings white blood cells to the area to fight off any pathogens that may be present

Question 16

Wound repair

Answer 16

The skin is able to repair itself in the event of injury and re-form a barrier against pathogen entry. The surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound. The tissue below the wound then contracts to bring the edges of the wound closer together. It is repaired using collagen fibres- too many collagen fibres and you’ll end up with a scar

Question 17

Expulsive reflexes

Answer 17

Expulsive reflexes include coughing and sneezing. A sneeze happens when the mucous membranes in th nostrils are irritated by things such as dust or dirt. A cough stems from irritation in the respiratory tract. Both coughing and sneezing are an attempt to expel foreign objects, including pathogens, from the body, they happen automatically

Question 18

What is an antigen?

Answer 18

An antigen is a protein or glycoproteins on the cell surface membrane that stimulates an immune response such as producing antibodies

Question 19

Describe the process of phagocytosis

Answer 19

1. A phagocyte recognises the antigens of a pathogen
   2: the cytoplasm of the phagocyte moves round the pathogen, engulfing it. This may be made easier by the presence of opsonises- molecules in the blood that attach to foreign antigens to aid phagocytosis
2. The pathogen is now contained in a phagosome
3. A lysosome fuses with the phagosome and breaks down the pathogen
   The phagocyte then presents the pathogens antigens. It sticks the antigens on its surface to activate other immune system cells. When a phagocyte does this it is acting as an antigen- presenting cell

Question 20

Define the term specific immune response

Answer 20

Response to an antigen which involves B/T lymphocytes or making antibodies

Question 21

Draw the structure of an antibody

Answer 21

Y shape
Constant region
Disulphide bridge holding polypeptides together
Hinge region allows flexibility when binding
Site that bonds to antigens (variable region)

Question 22

Which part of an antibody is complementary shape to the antigen?

Answer 22

Binding site

Question 23

The 4 ways in which an antibody works?

Answer 23

1) agglutinins stick pathogens together
2) Antitoxins neutralise toxins
3) Osponins help phagocytes engulf bacteria
4) others prevent pathogens from binding to human cells

Question 24

What is agglutinins?

Answer 24

Antibody- antigen complexes hold many pathogens together in large clumps. Process called agglutination
The pathogens are now too large to enter the host cells and are more likely to be engulfed by phagocytes such as macrophages and neutrophils

Question 25

Describe Antitoxins

Answer 25

Antibodies can cause molecules to be inactivated eg toxins and so prevents the toxins from entering the body cells - renders them harmless

Question 26

Opsonins

Answer 26

Opsonins are antibodies that bind to a pathogen and make it easier for them to be engulfed by neutrophils
These opsonins can bind to receptors on phagocytes - neutrophils/macrophages

Question 27

Describe how the structure of an antibody is adapted to its function (7 marks)

Answer 27

Antibodies are proteins made up of 4 polypeptide chains- 2 light and 2 heavy chains.
The antibody is a Y shaped molecule
The constant region binds to phagocytes and acts as a marker (opsonisation)
The variable region has the complementary shape to a specific antigen on the pathogen. There are two binding sites in this variable region
The hinge region allows flexibility so that the variable regions can bind to more than one antigen
The binding of antibody to antigen allows agglutination and neutralisation of toxins

Question 28

State two differences between the primary and secondary response

Answer 28

Secondary response starts earlier/ shorter delay before response
Secondary response is more rapid
Secondary response produces more antibodies

Question 29

Describe two types of active immunity

Answer 29

Natural- this is when you become immune after catching a disease. E.g if you have measles as a child, you shouldn’t be able to catch it again in later life
Artificial- this is when you become immune after being given a vaccination

Question 30

Describe the two types of passive immunity

Answer 30

Natural- this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk
Artificial- this is when you become immune after being injected with antibodies from someone else e.g if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations

Question 31

Describe the role of memory cells when the influenza virus enters the body

Answer 31

Memory cells recognise the antigen
Quickly divide to form a clone
If they are B memory cells they can differentiate into plasma cells
And make antibodies against the virus
Or if T memory cells they can differentiate and change into t killer cells
These memory cells are responsible for the secondary response- they destroy the virus before symptoms appear

Question 32

Describe and explain how resistance may evolve in a population of bacteria

Answer 32

In any population of bacteria there is genetic variation
Due to mutations
(Some bacteria will possess an allele which means that they are resistant to antibiotics. Some bacteria do not have this allele)
Those bacteria with the allele for resistance will be selected for when antibiotics used( selection pressure )
When antibiotics are used those individual bacteria with the allele will survive reproduce and pass on their alleles to the next generation
The proportion of the population with this resistance allele will increase