communicable diseases paper 2

define communicable diseases

diseases that can be passed from one organism to another

what are the four types of pathogens

1. bacteria

2. viruses

3. fungi

4. protoctists (protists)

what microorganism produces toxins that damage body cells

bacteria

what microorganism uses host cells to replicate before bursting out and destroying cells

viruses

what microorganism take over cells and break them open

protoctists (protists)

what microorganism digests living cells to destroy them, aswell as some produce toxins

fungi

how could direct transmission take place

• direct contact- skin-to-skin contact, kissing, sexual intercourse

• airborne droplets- coughing or sneezing tiny droplets of saliva or mucus oonto someone

how could indirect tramsmission take place

• food and drinking water

• vectors

• contaminated objects

what are vectors

organisms that transmit pathogens from one host to another

how could living conditions increase the risk of infection

overcrowded areas increase the risk of direct transmission

give an example of how climate increases the risk of infection

water temperatures allow mosquiotes to breed and transmit malaria

how could social factors increase the risk of infection

a lack of health education and healthcare systems increases the risk of communicable diseases

give examples of bacterial diseases

1. tuberculosis

2. bacterial meningitis

give examples of viral diseases

1. HIV/AIDS

2. influenza

give examples of fungal diseases

1. athlete’s foot

2. ringworm

give an example of a protoctist-causes disease

malaria

what effect does tuberculosis have on the body

damages the lungs and suppresses the immune system

what effect does bacterial meeningitis have on the body

damages membranes of the brain and can cause blood poisoning

what effect does HIV/AIDS have on the body

gradually destroys the immune system/ weakens the immune system

how does influenza effect the body

kills ciliated epithelial cells in the gas exchange system

what effect does athlete’s foot have on the body

causes cracking and scaling of skin between the toes

what effect does ringworm have on the body

causes a circular, red rash

what effect does malaria have on the body

damages the red blood cells, liver and brain

how is tuberculosis transmitted

airborne droplets, contaminated food and drink

how is bacterial meningitis transmitted

airborne droplets

how is HIV/AIDS transmitted

exchange of bodily fluids

how is influenza transmitted

airborne droplets, contaminated objects

how is athlete’s foot transmitted

contaminated objects

how is ringworm transmitted

direct contact

how is malaria transmitted

vector (mosquitoes)

how can direct transmission happen in plants

it involves the direct contact of a healthy plant with a part of an iinfected plant

how does indirect transmission happen in plants

• soil contamination 9infected plants leave pathogens or spores in the soil)

• vectors

in plant disease, what are examples of vectors

• wind- spores carried by wind

• water- spores travel on surface of water to reach uninfected plants

• animals- insects and birds carry pathogens or spores from one plant to another

• humans- pathogens and spores transmitted from handling plants, clothing, farming tools and practices

in plants, what factors increase the chances of communicable disease

• crop variety- some more susceptible than others

• overcrowding- increases likelihood of direct contact

• mineral nutrition- poor nutrition reduces resistance of plants

• climate change- increased rainfall and wind increase the spread of disease

name a bacterial plant disease, state what plants it affects, and what effects it has

ring rot

affects potatoes, tomatoes and aubergines

damages the leaves and fruit

name a viral plant disease and name the plants it affects and how it affects them

tobacco mosaic virus

affects many plant species including tobacco, tomato, red peppers

damages the leaves and fruit

name a fungal plant disease, the plants affected, and the effect it has on the plant

black sigatoka

banana plants

attacks and destroys leaves, turning them black

name a protoctistal plant disease, the affected plants, and the effect it has on the plants

potato/tomato blight

potatoes and tomatoes

destroys leaves and fruit

list plant physical defences, and explain how they work

1. waxy cuticles- leaves and stems covered in waxy cuticle which provides a physical barrier

2. cell walls- forms a physical barrier against pathogens

3. production of callose- when plants are attacked by pathogens they produce a polysaccharide called callose. this is deposited between the cell wall and the cell surface membrane to make it harder for pathogens to enter cells

how does callose act as a physical barrier

• when plants are attacked by athogens they produce a polysaccharide called callose.

• it is deposited between the cell wall and the cell surface membrane to make it harder for pathogens to enter cells

list some plant chemical defences

• insect repellents- reduce the number of insects feeding on plants to prevent them from transmitting pathogens

• insecticides- kill insects to prevent them from transmitting pathogens

• antibacterial substances- chemicals such as antibiotics are produced to kill bacteria o inhibit their growth

• toxins- some plants produce chemicals that break down into cyanide when plant cells are attacked

what is the difference between non-specific and specific defence mechanisms

• non-specific- response is the same for all pathogens (act quickly)

• specific- response is specific to each pathogen (act slowly)

give examples of non-specific defence mechanisms

• physical and chemical barriers

• phagocytosis

give examples of specific defense mechanisms

• cellular response

• humoral response

how does the skin act as a physical and chemical barrier

• physical barrier because it block pathogens from entering the body

• chemical barrier because it produces sebum- an oily, antimicrobial substance that lowers pH to inhibit the growth of pathgens

how do mucous membranes act as a barrier

• parts of the ears, nose, throat and digestive tract are lined by mucous membranes

• the membranes secrete mucus to trap pathogens and use lysozymes to destroy them

how do expulsive reflexes act as a barrier

• coughing and sneezing are methods for expelling foreign objects from the gas exchange system

• vomiting and diarrhoea expel the contents of the gut along with any pathogens present

how does clotting and wound repair act as a barrier

• a cut to the slin provides possible entry to pathogens, so blood clots act quickly to seal and wounds

• the clot dries to form a scab that blocks entry to the body

• after a scab has formed, the skin is capable of repairiing itself to reform its physical barrier

• epidermal cells underneath the scab divide while damaged blood vessels regrow and collagen fibres are used to provide strength to the new tissue

• once the epidermis is the required thickness, the scab breaks off and the wound is healed

what are the two ways a damaged tissue could trigger inflammation

1. blood vessels dilate which increases blood flow to the area, making it hotter to prevent pathogens from reproducing

2. blood vessel walls become more permeable so that they start to leak tissue fluid, causing swelling and isolating any pathogens in the damaged tissue

what are antigens and what do they do

antigens are unique proteins found on the surface of cells

they allow the immune system to distinguish between the body’s own cells 9containing self anitgens) and foreign cells (containing non-self antigens)

what molecules do antigens allow the immune system to identify

• pethogens- immune system recognises antigens as being foreign

• abnormal body cells- cancerous of infected cells have abnormal antigens

• toxins- toxins are antigen molecules themselves

• cells from other organisms of the same species- may have different antigens to the body’s own cells and no are identified as being foreing. this can cause rejection of donated organs.

is phagocytosis a specific or non-specific defense mechanism

non-specific

what are phagocytes

a type of white blood cell that engulf and destroy pathogens.

describe the two main types of phagoctye

1. neutrophils- these rapidly engulf and destroy pathogens at the site of infection

2. macrophages- these engulf and digest pathogens but also present the pathogen’s antigens on its cell surface to activate other cells in the immune system

describe the process of phagocytosis

1. the pathogen releases chemicals that attract a phagocyte

2. the phagocyte recognises the pathogen’s antigens as non-self. This causes the phagocyte to bind to the pathogen

3. the phagocyte engulfs the pathogen

4. the pathogen is now contained within a vesicle called a ‘phagosome’

5. the lysosome (within the phagocyte), containing hydrolytic enzymes called lysozymes, fuses with te phagosome to form a phagolysosome.

6. lysozymes digest and destroy the pathogen

7. the phagocyte presents the pathogen’s antigens on its surface to activate other cells in the immune system. The phagocyte is then referred to as an antigen-presenting cell (APC)

what organelle within the phagosome contains hydrolytic enzymes

the lysosome contains lysozymes

what are cytokines and how do they work

1. cytokines are chemicals released by phagocytes that have just engulfed a pathogen.

2. they attract other phagocytes to the site of infection

3. they also trigger an increase in body temperature, which inhibits the reproduction of pathogens.

what are opsonins and how do they work

1. opsonins are chemicals that bind to pathogens to make them easily recognisable by phagoctyes

2. phagocytes contain receptors on their cell-surface which bind to common opsonins, making it easier for the phagocyte to bind to the pathogen and destroy it.

what type of white blood cell does the specific immune response depend on

lymphocytes (T and B)

what is the difference between T lymphocytes and B lymphocytes

• T lymphocytes mature in the thymus gland. They are involveed in the cellular response where they respond to antigens presented on body cells

• B lymphocytes mature in the bone marrow. They are involved in the humoral response where they produce antibodies found in body fluids

list the 4 types of T cell/ T lymphocytes

• T helper cells

• T killer cells

• T regulator cells

• T memory cells

what are T helper cells

• have receptors on their cell-surface that bind to complementary antigens on antigen-presenting cells

• they produce interleukins (a type of cytokine) which stimulates B cells or phagocytes

• they can also form memory cells or T killer cells

what are T killer cells

• they kill abnormal and foreign cells by producing a protein known as perforin

• this protein makes holes in the cell-surface membrane, causing it to become freely permeable and causing cell death

what are T regulator cells

• suppress the immune system after pathogens have been destroyed

• this helps to prevent the immune system from mistakenly attacking body cells

what are T memory cells

• provide long-term immunity against specific pathogens

• provide a rapid response if the body is re-infected by the same pathogen

what are the stages of cellular response

1. macrophages engulf pathogens and display their antigens on the cell-surface. They are now known as antigen-presenting cells

2. t helper cells with complementary receptors bind to these antigens

3. on binding, the T helper cell is activated to divide by mitosis to form genetically identical clones

4. (the clones T cells can carry out other functions)

what functions can be carried out by cloned T cells

• develop into memory cells

• develop into killer T cells

• stimulate phagocytosis

• stimulate division of B cells

list the cells involved in the humoral response

• B cells

• plasma cells

• memory cells

• helper T cells

describe B cells

• have antibodies on their cell-surface membrane that bind to complementary antigens

• on doing so, they engulf the antigens and display them on their cell-surface to become antigen-presenting cells

• once activated, B cells can divide into plasma cells and memory cells

describe plasma cells

• types of B cell that can produce and secrete antibodies against a specific antigen

• they have a short lifespan of only a few days

what are memory cells

• types of B cell that provide long-term immunity against specific pathogens

• they have a much longer lifespan than plasma cells

• they repidly divide into plasma cells if the body is re-infected by the same pathogen

how are helper T cells involved in the humoral response

they bind to antigen-presenting cells to activate the divison of B cells

describe the stages of the humoral response

1. a B cell with a complementary antibody binds to the antigens on a pathogen

2. the B cell engulfs the pathogen and presents its antigens on the cell-surface membrane to become an antigen-presenting cell.

3. (clonal selection)- activated T helper cell binds to the B cell, causing activation of this B cell.

4. (clonal expansion)- the activated B cell divides by mitosis to form plasma and memory cell clones.

5. the cloned plasma cells produce and secrete the specific antibody which is complementary to the antigen on the pathgen’s surface. These antibodies attach to antigens on pathogens and destroy them

6. the memory cells circulate the blood and tissue fluid, ready to divide if the body is re-infected by the same pathogen

define ‘clonal selection’ in the humoral response

the B cell with the correct antibody is selected for cloning (by being activated by a helper T cell)

define ‘clonal expansion’ in the humoral respoonse

the division of specific B cells to produce genetically identical clones

in the primary immune response, is the production of antibodies slower or faster than in the secondary immune response

slower because there are very few B cells that are specific to the pathogen’s antigens, and it takes time for the B cells to divide into plasma cells.

in the secondary response, the memory B cells recognise the pathogen’s antigens and quickly divide into plasma cells. The plasma cells secrete large numbers of antibodies and quickly destroy the pathogen

are symptoms experienced in the seconday immune response

no

what are autoimmune diseases and give examples

• when the immune r=system cannot recognise ‘self’ antigens, so its starts to attack them

  examples

• type 1 diabetes (immune system attacks the insulin-secreting cells of the pancreas, causing a lack of insulin)

• lupus

• rheumatoid arthiritis

describe the structure of antibodies

• Y shaped glycoproteins made up of four polypeptide chains (two heavy chains, and two light chains)

• the polypeptide chains are held together via disulphide bridges

• contain a constant region and a variable region

what is the constant region in antibodies

it is the same for all antibodies and it binds to receptors on cells such as B cells

what is the variable region on antibodies

it is different for each antibody as its shape is complementary to a specific antigen. it is the part of the antibody that binds to antigens

what is it called when an antibody binds to an antigen

an antigen-antibody complex

what three roles do antibodies do to help destroy pathogens

1. agglutination of pathogens

2. neutralisation of toxins- this is when antibodies bind to toxins to inactivate them

3. preventing pathogens from binding- when antibodies bind to pathogens to stop them from infecting body cells

what is the agglutination of pathogens

it involves clumping pathogens together to enable easier phagocytosis:

• antibodies act as aglutinins, causing pathogens to clump together.

• antibodies also act as opsonins, making pathogens easily recognisable by phagocytes

how do antibodies perform the neutralisation of toxins

• antibodies can act as antitoxins where they bind to toxins produced by pathogens

• this binding neutralises (inactivates) the toxins to prevent them from damaging body cells

how do antibodies prevent pathogens from binding to cells

• when antibodies bind to a pathogen’s antigens, they block cell-surface receptors needed to bind to host cells.

• this means that the pathogen cannot bind to or invade host cells

what is active immunity

immunity developed after the immune system makes its own antibodies

what is passive immunity

immunity acquired by receiving antibdies from another organism

how do vaccinations provide immunity

1. the vaccine, containing antigens, is injected into the blood

2. this stimulates the primary immune response to produce antibodies against the pathogen

3. memory cells, capable of recognising these antigens, are produced

4. on second exposure to this pathogen, memory cells rapidly divide into plasma cells

5. plasma cells repidly produce antibodies against the pathogen

6. the pathogen is destroyed before any symptoms are experienced

what may vaccines contain

• dead or inactive pathogens

• weakened pathogen strains

• a harmless version of a toxin

• isolated antigens from a pathogen

• genetically engineered antigens

what factors affect the success of a vaccine

• availability

• minimal side effects

• herd immunity

• administration

• infrastructure

how does herd immunity work

• manyt people are vaccinated, meaning that most people are immune to the disease and cannot transmit the pathogen to others

• this reduces the chance of non-vacciinated individuals catching the disease

• as a result, fewer individuals become infected

what is antigenic variability

when a pathogen changes its antigens so that they are no longer recognised by the immune system

how can antibiotics affect bacteria

• prevent the synthesis of bacterial cell walls

• disrupt protein activity in the cell membrane

• disrupt enzyme action

• prevent DNA synthesis

• prevent protein synthesis

how do antibiotic resistant bacteria occur

1. genetic mutations occur, making some bacteria resistan to an antibiotic

2. when an infection is reated with antibiotics, resistant bacteria are able to survive

3. resistant bacteria reproduce, passing on the allele for antibiotic resistance to their offspring.

   (NATURAL SELECTION)

what measures can be taken to reduce the development of antibiotic resistant bacteria

• choosing appropriate antibiotics for treatment

• using anibiotics only when needed

• avoiding the use of wide0spectrum antibiotics

• ensuring patient completes course of antibiotics

• avoiding the use of antibiotics in farming