Eduqas A Level Biology: Component 3: "Immunology"

Define pathogen

An organism that causes damage to it's host

Define infectious

A disease that may be passed or transmitted from one individual to another

Define carrier

A person who shows no symptoms when infecred by a disease organism but can pass the disease to another individual

Define disease reservoir

Where a pathogen is normally found: this may be in humans or another animal and may be a source of infection

Define endemic

A disease which is always present at low levels in an area

Define epidemic

Where there is a significant increase in the usual number of cases of a disease often associated with rapid disease spread.

Define pandemic

An epidemic occuring worlwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people

Define vaccine

Uses non-pathogenic forms, products or antigens of microorganisms to stimulate an immune response which confers protection against subsequent infection

Define antibiotic

Substances produced by microorganisms which affect the growth of other microorganisms

Define antibiotic resistance

Where a microorganism which should be infected by an antibiotic is no longer susceptible to it

Define vector

A living organism which transfers a disease from one individual to another

Define toxin

A chemical produced by a microorganism which causes damage to its host

Define antigenic types

Organisms with the same or very similar antigens on the surface. Such types are sub groups or strains of a microbial species which may be used to trace infections. They are usually identified by using antibodies from serum

Define antigen

A molecule that causes the immune system to produce antibodies against it. These may be individual molecules or those on the surface of cells

What are the key organs of the immune system?

Bone marrow and thymus glands

Describe the difference between granulocytes and agranulocytes.

Granulocytes: lobed nucleus & the granules are lysosomes for phagocytosis

Agranulocytes: spherical nucleus & produce antibodies

What type of organism is cholera, what is its source of infection, which tissue does it affect and what symptoms are caused?

Gram negative bacterium
Source is contaminated water supplies
Affects the human gut lining
Symptoms are watery diarrhoea, severe dehydration and often death

How is cholera transmitted, how is it prevented and what are the control methods and treatment?

TRANSMISSION: By drinking contaminated water
PREVENTION: treatment of water, clean drinking water and good hygiene
CONTROL METHODS & TREATMENT: Rehydration and vaccines

What type of organism is tuberculosis, what is its source, what type of tissue does it affect and what are the symptoms it presents?

Bacteria
Sourced by other infected individuals in close proximity
Affects lung and neck lymph nodes
Symptoms include coughing, chest pains and coughing up blood

How is tuberculosis transmitted, prevented and how can it be treated?

TRANSMISSION: airborne droplets, coughing & sneezing
PREVENTION: BCG vaccination and programme
TREATMENT: A long course of antibiotics

What type of organism is smallpox, what is its source of infection, what tissue does it affect and what symptoms does it display?

Virus
Sourced by other infected individuals in close proximity
Affects small blood vessels of the skin, mouth and throat
Symptoms include a rash and blisters

How is smallpox transmitted and what are its preventative/treatment measures?

TRANSMISSION; airborne droplets
PREVENTION/CONTROL: now extinct due to immunisation programmes

Why were the immunisation programmes for smallpox so successful?

Smallpox had a low rate of antigenic variation/mutation

What type of organism is influenza, what is its source of infection, what tissue does it affect and what symptoms are displayed?

3 main subgroups of a virus with many antigenic types
Sourced by other infected individuals in close proximity
Affects respiratory tract
Symptoms include a sore throat, coughing and a fever

How is influenze transmitted, what are its preventative measures and its treatment?

TRANSMISSION: airborne droplets
PREVENTION: Quarantine and hygiene but its difficult to control
TREATMENT: annual vaccination programmes but these are ineffective

Why are the annual vaccination programmes for influenza ineffective?

The virus has many new strains and antigenic types so its hard to target it.

What type of organism is malaria, what is its source of infection and what tissue does it affect?

Protoctistan parasite
Sourced at female mosquitoes acting as vectors when making a blood meal
Affects liver and red blood cells causing them to burst

What symptoms does malaria cause?

Fever, abdominal pain, headache, diarrhoea, nausea

What genus does malaria belong to?

Plasmodium

Why are male mosquitoes not vectors of the plasmodium parasite?

Only female mosquitoes take blood meals because they need the blood for their eggs

Outline the life cycle of the plasmodium parasite

1. Infected mosquito takes a blood meal and plasmodium enters the blood stream
2. Plasmodium enters the liver cells and mature
3. Liver cells rupture and release the parasites, which invade red blood cells and repeat the process
4. Parasites infect mosquito which takes a blood meal who will act as a vector once again

Explain some biological controls for the prevention of malaria

1. Introduce fish into the water so they can eat the aquatic larvae
2. Infect mosquito with bacterum to block plasmodium development in the mosquito
3. Sterilise male mosquitoes with X-rays so they cant provide offspring

Explain some preventative measures to prevent malaria that are based on mosquito behaviour

1. Sleep under nets since mosquitoes feed at night
2. Place a film of oil on water to prevent larvae from piercing the surface for oxygen
3. Spray indoor walls with insecticide to kill mosquitoes when they rest after feeding
4. Treat nets with insecticide
5. Drain or cover stagnant water to remove access for female mosquitoes to lay eggs

Why are vaccines ineffective against malaria?

Plasmodium parasite has a high mutation ratw

Describe ways in which viruses can be pathogenic

1. Production of toxic substances
2. Immune suppression
3. Cell lysis
4. Cell transformation where viral DNA integrates into the host chromosome and can cause rapid cell division

Why are viruses outside the host cell described as inert?

They can only replicate once they've hijacked the host cell's enzyme machinery

Describe the lytic cycle.

Viruses enter a cell and immediateky reproduce using the hosts metabolism. Once the new virions are assembled in the cytoplasm, they leave either by lysis or budding from the host cell surface

Describe the lysogenic cycle

Virus' penetrate the cell and then integrate their nucleic acid into the host cell genome. They may remain for several cell generations and be copied. Then they enter the lytic cycle and symptoms are produced

What are the two types of antibiotics?

Bacteriostatic- prevents growth of bacteria
Bactericidal- kill bacteria

What type of organism produces antibiotics?

Fungi

What type of antibiotic is penicillin and how does it work?

Bactericidal
It prevents the formation of crosslinkages in the bacterial peptidoglycan cell wall by acting as a noncompetitive inhibitor for the enzyme

Why are viruses not affected by antibiotics?

They dont have a cell wall or metabolic pathways to disrupt

How might the overuse of antibiotics lead to antibiotic resistance?

Bacteria have a high mutation rate so natural mutations may give them resistance to an antibiotic. Overuse of bacteria leads to accidental selection of bacterial strains that are resistant since non resistant bacteria are wiped out and the frequency of the resistant allele increases

List the natural barriers the body has as a passive immune response

Skin flora, the skin, phagocytosis, blood clotting, mucus and ciliated epithelial cells & tear ducts, saliva and the stomach

How does blood clotting act as a passive immune response?

If the capillaries are broken, blood clots prevent the entry of pathogens

How do tear ducts, saliva and stomach acid act as a passive immune response?

Lysozyme in the tears and saliva hydrolyse peptidoglycan cell walls to kill bacteria. Stomach acid kills many bacteria

How is phagocytosis a passive immune response?

A phagocyte engulfs a bacterium, enclosing it in a vacuole. Lysosomes fuse with the vacuole and release hydrolytic enzymes to destroy the bacteria

How do skin flora act as a passive immune response?

Bacteria and fungi found on the skin offer competition for pathogenic bacteria

How does the skin act as a passive immune response?

It covers the external surface

How might inhaled air containing microorganisms be fought against?

Mucus traps the microorganisms and ciliated epithelial cells waft to bring the mucus up and out of the trachea

What are lymphocytes?

Subgroups of leucocytes that are produced from stem cells in the bone marrow

Where are B lymphocytes activated?

In the blood, spleen and lymph nodes

Describe what occurs in the humoral response of the specific immune response.

A B lymphocyte with a specific receptor binds to a specific antigen on the pathogen. This stimulates the B lymphocyte to undergo clonal expansion and divide by mitosis. Differentiation then occurs and B lymphocyte memory cells are produced which remain dormant in the blood until the same antigen is reencountered. Plasma b cells are also made and they secrete antibodies specific to the antigen.

What is the protein name for antibodies?

Immunoglobulins

What type of bond holds the antibody together?

Disulfide bridges

What is agglutination?

The antibodies bind to a bacteria through a specific receptor and clump them together to allow phagocytes to locate and engulf said bacteria.

Describe the strcture of an antibody.

Y shaped heavy chains with outer light chains. The bottom region is constant and the top region is the variable region since the tips of the y are complementary to the shape of the antigen

Where are T-lymphocytes activated?

In the thymus gland

Describe the cell mediated response.

A phagocyte engulfs a pathogen and then presents its antigens on its membrane surface, becoming an antigen presenting cell. A T lymphocyte detects the antigen on the antigen presenting cell and is stimulated to undergo clonal expansion by mitosis. Differentiation then occurs making T memory cells, T helper cells and Cytotoxic T cells.

What other cells can becoming antigen presenting cells apart from phagocytes?

Infected body cells and B lymphocytes.

Describe the roles of the 3 cells T lymphocytes differentiate into.

T HELPER CELL: produce cytokines which stimulate more phagocytic cells to migrate to the infected tissue and engulf more pathogens. Cytokines also stimulate clonal expansion of plasma B cells to secrete more specific antibodies
T MEMORY CELL: remain dormant until the same antigen is reencountered, stimulating clonal expansion again
CYTOTOXIC T CELL: kills infected body cells by lysis

Why is the latent period in the primary reponse longer than that in the secondary reponse?

Its the period where the cell is being found

After the primary response, for how long do the plasma B cells continue to secrete a low level of antibodies?

3 weeks

Describe the secondary immune response

On reexpoaure, theres a very short latent period and then memory cells undergo rapid clonal expansion. Theres a rapid production of plasma B cells so a rapid and more concentrated production of antibodies. The antibodies remain at high concentrations for longer so theres no symptoms.

Describe passive immunity and give examples

The body recieves antibodies made by another individual for shortlived protection. The antibodies are recognised as nonself and are destroyed so no memory cells are produced.

E.g. in breast milk, through placenta to the foetus, injection

Describe active immunity and give examples.

The individual produces their own antibodies and produces memory cells.

E.g. natural response to infection, vaccination

Describe the different forms of vaccinations

1. Isolated antigens
2. Weakened or attenuated versions of the pathogen
3. Inactivated toxin
4. Inactive or killed pathogen

When might antibodies be injected into someone?

In an emergency when the person's immune system needs time to develop an active immune response or for people who have a weakened immune response

Why are flu vaccinations given annually?

There are many antigenic types of influenza and new types always occur due to high mutation rates. The vaccination contains a few new strains that are predicted to be most prevalent that year.

What is herd immunity?

When enough people are vaccinated in a population so those that arent are still protected since the spread of disease is controlled.

Describe some ethical considerations for vaccination programmes.

Cost v. effectiveness
Side effects, even if percieved
Protection of the individual compared the protection of the community
The rights of the individual in mandatory v. voluntary programmes