OCR A Biology - Communicable Diseases

What are the 4 pathogens?

bacteria, viruses, fungi, and protoctista

What is a pathogen?

A microorganism that carries and causes disease

What are the 2 ways bacteria is classified?

By their shape and their cell wall

What is the basic structure of a virus?

DNA or RNA surrounded by a protein coat (capsid)

What is a virus and it's role? Give 2 examples in humans and 1 in plants

A virus invades the cell metabolism and takes over another cells genetic machinery by inserting it's genetic material into the host DNA. The virus replicates inside using the host cell. When the host cell bursts, viruses are released defecting healthy cells. HIV, flu ( animals ) and TMV ( plants )

What is bacteria and it's role? Give 2 examples in humans and 1 in plants

Prokaryotic cells which divide by binary fission every 20 mins. They causes disease by producing toxins and waste products, damaging the host cell. Toxins break down cell membranes, inactivate enzymes or prevent cell division. Tuberculosis, meningitis ( animals ), ring rot ( plants )

What is fungi and it's role? Give 2 examples

Eukaryotic organisms that feed on decaying matter ( saprophytic ). They can be parasitic and cause communicable disease. Fungi consists of tube like structures called hyphae which form a mycelium under the skin. These secrete spores which travel long distances causing redness and irritation. In plants, they're inside the vascular tissue releasing extracellular enzymes to digest tissue and cause decay.

Examples : athletes foot ( animals ), black Sigatoka ( plants )

What are protists and their role? Give 2 examples

Eukaryotic cells which enter the host cell and feed on the contents of the cell. These divide before they break out. Examples are malaria ( in humans ) and potato blight ( plant )

What bacterium causes meningitis?

Streptococcus pneumonia

How is meningitis spread and prevented? What pathogen is it caused by?

Spread by droplet infection, prevented by antibiotics administered early enough or vaccines ( only protecting some forms )

Pathogen

Symptoms and mechanism of meningitis

Non blanching ( doesn't disappear from pressure with glass ) red/purple rash. Inflammation and infection of the meninges ( membranes surrounding the brain and spinal cord ) - spread to the rest of body and cause damage to nerves and brain ( septicaemia )

Symptoms of ring rot

Wilting, discolouration, leaf edges become brittle so no photosynthesis

What organisms do TB affect, and by what pathogen?

Affect humans, cows, pigs, badgers etc

Caused by bacteria

What bacterium causes TB? How is TB spread and prevented?

Mycobacterium/ M.Bovis. Spread by droplet infection ( coughing and sneezing from infected person in close proximity ). Milk and meat of infected cattle. Cured by antibiotics. Prevented by vaccination ( BCG), better standards of living, cover mouth when sneezing or coughing, ventilation by opening windows

How does the mechanism of TB work?

Enter lungs and engulfed by macrophages - bacteria reproduces inside and bursts of macrophages. Damages the lung tissue, suppresses immune system and therefore more susceptible to disease

What has TB not been eradicated?

- opportunistic disease - attacks a weakened immune system

- overcrowding - spread by droplet infection

- can be dormant in body, symptomless carriers

- vaccine is less than 100% effective

- low income countries cannot afford vaccines/ drugs

- antibiotic resistance as antibiotics need to be taken over long period of time ( DOTS ) - long course of treatment

How can pathogens be directly transmitted between animals?

- direct contact

- inoculation ( breaks in skin, animal bites )

- ingestion

How can pathogens be transmitted indirectly between animals?

- vectors ( water/insects )

- droplet infection

- fomites ( inanimate objects transfer pathogens )

How can pathogens be transmitted between plants?

- soil contamination

- vectors

What are common vectors?

- wind

- water

- animals

- humans

What affects the transmission of disease in plants?

- living conditions - damp, warm conditions increase the spread of pathogens and spores

- climate change - increased rainfall and wind cause spread of diseases

- varieties of crops susceptible to diseases

- over-crowding increases contact between plants

- poor mineral nutrition reduces resistance of plants

What is health?

A state of physical, mental and social well-being - absence of disease

Describe plant defences between pathogens

1) waxy cuticle which prevents the entry of pathogens - made up of cumin

3) lignin added to callose to make the mechanical barrier to invasion stronger

4) callose deposited between cell walls, cell membranes and in plasmodesmata between infected cells and healthy cells, prevents spread of pathogens

callose blocks sieve plates in phloem, sealing off infected part and prevents spread of pathogens

How does the mechanism of influenza work, and symptoms? Pathogen causing it?

Influenza attacks the lung epithelial tissue - vulnerable to secondary infections like pneumonia

Caused by virus

What pathogen causes HIV/AIDS?

Viruses

Human immunodeficiency virus

Acquired immunodeficiency virus

How does HIV make us ill?

They enter t-helper cells, replicate inside and burst open, destroying lympochytes. No immune response so more susceptible to diseases like tuberculosis and pneumonia

How is HIV/AIDS transmitted?

Unprotected sex through bodily fluids, blood transfusions/blood to blood contact, contaminated needles, placenta, breast milk

Explain why it is difficult to control the spread of HIV/AIDS and why it is higher in some parts of the world than others

- no cure

- no vaccine

- high mutation rate

- cannot be treated like with antibiotics

- dormant & long incubation period therefore symptomless carriers

- people refuse to be treated/ do not come forward due to stigma

- antigenic concealment ( hide inside cells )

- unprotected sex

Higher in other parts of world due to :

- poverty

- less education

- lower availability of condoms

- rape cases

- LIC have little hospitals to treat HIV

- drug abuse - used of shared needles

- infected breast feeding mothers

Explain how infection from HIV can increase the risk of a person developing diseases like TB

HIV affects T helper cells means a person is more susceptible

Why is HIV called a retrovirus?

Because it synthesizes DNA from the viral RNA template using the enzyme reverse transcriptase. This is the reverse ("retro") of the usual DNA --> RNA information flow. DNA inserted into host cell

What is a parasite?

Lives in the host and feeds on the nutrition from the host at the expense of the host

Explain why the human body defences do not prevent the entry of plasmodium in the body

The mosquito feeds on blood - therefore, the mosquito bites the skin and it can no longer act as a barrier

Suggest one reason why people be concerned about the use of insecticides

- insecticide resistance

- idea of bioaccumulation

- destruction of species is ethically wrong

- might cause unintended health problems in humans / to other species

State 3 biological reasons why it has not been possible to produce an effective vaccine for malaria

Different strains of plasmodium

Different antigens due to mutation/ variation

More than one stage in the life cycle within human; different stages require different antigens

So will need a different vaccine for both each strain and each stage

The parasite is concealed in cells and only exposed/ in circulation for a short time

Explain the lifecycle of a mosquito

1) Malaria-infected mosquito bites the individual and pierces the skin. A mosquito, female anopheles mosquito, is the vector carrying the parasite. The parasite is present in the mosquitos saliva. The parasite passes from the saliva to the blood during the feeding of the uninfected human

2) The parasite enters the liver cells, multiply, and rupture the cell. These cells burst and release more parasites into the blood

3) These parasites enter the red blood cells where they continue to multiply and rupture cells. These mosquitos reproduce asexually in the mosquitos.

4) Some of these parasites burst out of the RBC and exist as male and female reproductive cells ( gametophytes ), forming gametes

5) These gametocytes are transferred to another mosquito. The uninfected mosquito sucks on infected blood.

Asexual reproduction takes place in mosquito, sexual production in humans ( 2 different life cycles )

What parasite causes a malaria, and vector?

Plasmodium falciparum

Female anopheles mosquito

What does a female mosquito need to lay eggs?

2 blood meals to provide her with protein

How is malaria transmitted other bites?

- blood needles

- placenta

- surgical equipment

Why does malaria cause a person to feel sick and tired?

Feeds on haemoglobin so red blood cells burst. Less oxygen carried around the body

Suggest why adults who have survived malaria may lose their immunity when they leave a malarial area

No repeat infections/ no further exposure (to the antigen/ pathogen/ parasite)

Loss of immunological memory

Limited life for memory cells

No secondary response

Explain why it is hard to discover new drugs

- first discovered in its natural environment

- biodiversity is reduced

- habitat destruction ( eg deforestation )

Why does mosquitos spend part of its life cycles in erythrocytes?

- use red blood cells to hide from immune system

- used as food source

- can multiply and rupture cells

Why is it good for malaria to reproduce asexually in red blood cells?

- no need to find a mate

- rapid multiplication

- spreads quickly before immune system destroys it

Why is malaria a difficult disease to control?

- protist - difficult to control

- resistance to anti-malarial drugs

- resistance to insecticides

- virus so mutation leads to new strains

- different vaccine needed for each strain

- parasite hides in red blood cells to hide from immune system ( antigenic concealment )

- multiple life stages in life cycle

- mosquito breeds quickly in stagnant water

- inadequate housing

- increase in climate change with increase in areas ( tropics )

Describe the body's primary ( first ) non specific ( targets all microorganisms ) defences to pathogen entry

Skin - acts as physical barrier to prevent entry of microorganisms, produces sebum which inhibits pathogen growth

Airways, lungs and digestive system lined with goblet cells - produce mucus to trap pathogens ( MUCOUS MEMBRANES )

Ciliated epithelium which wafts mucus from lungs

Blood clotting so pathogens do not enter blood

Wax to trap pathogens

Tears and saliva contain lysozymes - kills bacteria due to hydrolytic enzymes

Expulsive reflexes

What is the skin epidermis made up of?

Keratinocytes produced by mitosis at base. These dry out the cytoplasm, and replaced by keratin ( keratinisation ). Keratinised layer is a barrier to pathogen entry

Describe the blood clotting cascade

1) damage to tissue/blood vessel exposes collagen

2) platelets are release and bind to collagen

3) platelets become activated and stick to eachother to form a temporary platelet plug

4) clotting factors are released to reinforce the platelet plug

5) damaged cells and activated platelets release thromboplastin, which converts prothrombin to thrombin ( requires calcium ions )

6) thrombin acts as an enzyme converting fibrinogen to fibrin

7) fibrin forms a mesh of fibres in which platelets and blood cells can be trapped

8) fibrin polymerises and dries to form a scab, preventing bleeding

Describe the structure of an antibody

protein that form a Y shape made of 4 polypeptide chains - composed of 2 heavy chains and 2 light chains

It has a variable region which is complementary and specific to an antigen - it has more than one ( ANTIGEN BINDING SITE )

Hinge region allows for flexibility so it can bind to more than one antigen

Constant region which allows it to find phagocytes and therefore aids phagocytosis

What are antigens?

Proteins on the cell surface membrane of foreign cells ( eg pathogens ) that stimulate the immune response

What kind of proteins are antibodies?

glycoproteins called immunoglobulins

How does the antibody act as an opsonin?

They increase the chance of phagocytosis

Antibody binds to the pathogen and the phagocyte ( phagocyte can bind to constant region, antigen binds to variable region )

How do antibodies use agglutination?

They have multiple binding sites for pathogens to bind to

Clump together many pathogens so they are too large to enter the host cell and therefore impedes function

Therefore increase the likelihood of phagocytosis

How do antibodies use neutralisation?

They cover the binding sites on pathogens or bind to toxins to form antitoxins

Prevent the binding or entry of pathogens into the host cell

What is the difference between passive and active immunity?

Passive: immunity that results from injection of antibodies from another person

Plasma cells do NOT produce antibodies so no long term immunity

Active: immunity that results from body creating it's own antibodies following exposure to pathogen

Plasma cells produce antibodies so long term immunity

What is the difference between natural passive and natural active immunity?

Natural passive

Antibodies are introduced into the body from another source, so it does not trigger an immune response - plasma cells do not make antibodies

Eg placenta, breast milk, breast milk

Natural active

Eg being infected or suffering from a disease

What is the difference between artificial active and artificial passive immunity?

Artifical passive

Injection of antibodies made by another individual ( tetanus for eg )

Artificial active

Weakened or dead pathogen is introduced into the body by the vaccination ( eg TB, influenza )

What is an autoimmune response? Give examples

Abnormal immune response against tissues in the body

Antibodies can no longer recognise self antigens and treats them as foreign

Antibody and antigen no longer complementary

Examples include - lupus, arthritis, type 1 diabetes

Who found the pencillin antibotic?

Alexander Fleming

What is the function of docataxel?

From yew trees

Used for cancer treatment

What is the function of digoxin?

Extracted from foxgloves

Used to treat heart conditions

What issues come with antibiotics?

May kill ' good bacteria ,

Resistant strains of bacteria ( eg MRSA )

How has resistant strains of bacteria evolved?

Genetic variation within a population

Random mutation arises

Gives rise to the antibiotic resistance allele

Antibiotics are the selection pressure

Allele coding for antibiotic resistance is passed onto offspring, and increase in allele frequency over time and many generations

Why is it important to maintain biodiversity?

Increases the gene pool

Population is more likely to withstand a change

Source of potential medicines

Explain the secondary non specific defences

Histamines are released by mast cells that detect the infection.

Arterioles dilate ( so increased blood flow to the area ) causing localised heat and redness. This inhabits pathogen reproduction.

Capillaries become more leaky for the formation of tissue fluid by swelling. This can lead to a build up of tissue fluid. White blood cells also leave the blood into tissue fluid and more fluid enters the lymphatic system.

Cytokines are also used for cell signalling to attract phagocytes to the site of infection. Pathogens can then be disposed of by phagocytosis.

How does the lymphatic system work?

Excess tissue fluid is drained into the lymphatic system

Pathogens enter the lymph

Transported to the lymph nodes

Lymph nodes become swollen and produce lymphocytes and phagocytes

How do cytokines attract pathogens to the site of infection?

By chemotaxis ( movement of chemicals )

How does phagocytosis occur?

1) pathogen is surrounded by the phagocytes cytoplasm

2) endocytosis occurs and pathogen is engulfed and enclosed in a vacuole

3) this forms a phagosome

4) the phagosome contains lysosomes which fuse with the phagosome to form a phagolysosome

5) lysosome contains hydrolytic enzymes ( eg hydrogen peroxide, lysine etc ) to hydrolyse pathogen down into amino acids and sugars

6) these are expelled or absorbed into the cytoplasm

What are the 2 types of phagocytes?

Neutrophils and macrophages

Describe how a neutrophil would look on a microscope and it's features

Multi lobed nucleus

Features include :

- multilobed nucleus

- many lysosomes ( and other organelles )

- can therefore squeeze into the site of infection

Describe how a macrophage/monocyte would look on a microscope and it's features

Unilobular nucleus, less dishevelled than neutrophil

Travel in the blood as monocytes and settle in tissues as macrophages

How is an antigen presenting cell formed? Which phagocyte forms this?

When a pathogen is engulfed, it is not fully digested

Pathogen is hydrolysed by hydrolytic enzymes

Antigen is isolated and presented on the cell surface membrane

Shows other cells it is infected

MACROPHAGES

What is a lymphocyte? How does it look on a microscope?

It is a type of WBC

It is smaller than a phagocyte and has a round nucleus

What is the immune response?

Response to antigens through the production of antibodies

Describe the cell mediated response.

1) APC has antigens specific and complementary to receptors on T helper cell - occurs by clonal selection

2) these undergo clonal expansion by mitosis to form many different T cells

T helper cells

T cytotoxic cells - destroy body's infected cells by making holes in the cell surface membrane with perforins and hydrogen peroxide

T regulator cells - shut down response and end

T memory cells

Some T cells release interleukins ( cytokines ) to cause the clonal expansion of B cells to form B plasma and B memory cells

Compare defence mechanisms

Non specific - response is same for all pathogens

Includes phagocytosis, primary and secondary defences

Specific - response is slower and specific to each pathogen

Cell mediated response and humoural response

What is pus?

collection of dead neutrophils

Explain why it is not possible to protect yourself with one vaccine

Different pathogens have different antigens

Each antigen has a specific shape

Shape of the antibody must be complementary to the shape of the antigen

Explain the role of B cells in immunity

When B cells undergo mitosis, they differentiate into B plasma cells or B memory cells

B plasma cells produce antibodies ( short lived )

B memory cells ( long lives for decades in blood ) act as the immunological memory and can recognise the same antigen of the same pathogen again

B memory cells can rapidly divide into plasma cells when re infected with the same pathogen

This produces a large number of antibodies is pathogen is destroyed before symptoms occur

Compare the primary immune response to the secondary immune response

Primary immune response is on initial exposure to pathogen/infection, much slower due to clonal expansion, differentiation etc

Secondary immune response is just after infection, much faster due to B memory cells, more antibodies produced by B memory cells

Compare herd and ring vaccination

Herd vaccination is when you vaccinate a large percentage of the population so pathogen is not spread easily, and therefore protection for unvaccinated

Ring vaccination is when you vaccinate those vulnerable who were in contact with the person infected with pathogen