4.3 COMMUNICABLE DISEASES

Question 1

What is a pathogen?

Answer 1

A pathogen is a microorganism that causes disease.
- to cause disease, a pathogen must travel from host to host, get into tissues, reproduce and cause damage (symptoms)
- transmission of pathogens can be by vectors, physical contact, droplet infections or indirect contact

Question 2

What are the types of pathogen?

Answer 2

The types of pathogen is bacteria, fungi, viruses, protoctista

Question 3

How do you calculate the number of bacteria divisions?

Answer 3

Calculate the number of bacteria divisions:
2^n - where n = number of divisions
e.g 4 hours/20 minutes = 12 divisions
2^12 = 4096

Question 4

How does bacteria cause diease?

Answer 4

Bacteria causes disease by producing toxins and causing symptoms by cell damage. They can also damage cell membranes, enzymes or genetic material.

Question 5

What are the shapes of bacteria?

Answer 5

Shapes of bacteria:
- cocci (spherical) = have less surface area per volume than bacilli or spirillum, and thus can survive in dryer environments
- bacilli (rod shaped) and vibrio (curved) = have a greater SA:V ratio and can take up nutrients from dilute solutions more efficiently
- spirilli (spiral) = spiral cells, move with corkscrew motion, meet less resistance from surrounding water

Question 6

What is the structure of a virus?

Answer 6

Virus structure:
- very simple structures made up of 3 components
= nucleic acid
= protein coat
= lipid envelope
- non-living as they cannot replicate by themselves = manipulate their host cells to replicate them
-a bacteriophage is a virus that infects bacterial cells

Question 7

How is a bacteriophage made?

Answer 7

Bacteriophage production:
- lysogenic phase
1. the phage attaches to the host cell and injects its DNA into the cytoplasm
2. the phage DNA integrates itself into the bacterial chromosome becoming a prophage
3. the prophage remains latent and is replicated every time the host cell divides
- lytic phase
4. at a trigger the phage DNA is expressed to make phage proteins, which assemble into phage capsids
5. the bacterial cell bursts (lysis), releasing hundreds of phage particles

Question 8

How does a virus cause disease?

Answer 8

Virus causes disease:
1. virus attaches to host cell and the two membranes fuse, releasing the capsid into the cytoplasm
2. the viral enzyme reverse transcriptase synthesises ds DNA from the ss RNA. the DNA is incorporated into the host’s nuclear DNA where it is called a provirus
3. the provirus remains latent for years and is replicated every time the host cell divides
4. at a trigger the viral DNA is expressed to make viral proteins, which assemble in virus capsids
5. the virus particles are released by budding, collecting their lipid envelope from the host cell membrane

Question 9

How do fungi cause disease?

Answer 9

How fungi cause disease:
- some produce toxins which effect host cells
- some digest living cells (parasitic) and destroy cells
- fungal infections stop parts of plants photosynthesising and can quickly kill plants
- when fungi reproduce they produce spores which spread rapidly through crop plants

Question 10

How to protoctists transmit diease?

Answer 10

Protoctists:
- eukaryotes
- small percentage act as pathogens
- protists which cause disease are parasitic
- may need a vector to transfer them to their host (e.g malaria)
- may enter body through water (e.g aemobic dysentary)

Question 11

What is a disease?

Answer 11

A disease is a condition that has a negative effect on part/all of the body.

Question 12

What is health?

Answer 12

Health is mental and physical well-being.

Question 13

What is an infectious disease?

Answer 13

An infectious disease can spread between organisms and is transmitted between organisms.

Question 14

What is a vector?

Answer 14

A vector is an organism that carries a pathogen between hosts.

Question 15

What is an epidemic?

Answer 15

An epidemic is a fast spreading disease that is spread nationally and causes casualities.

Question 16

What is a pandemic?

Answer 16

A pandemic is a fast spreading disease that is spread globally and causes casualties.

Question 17

What is indirect transmission?

Answer 17

Indirect transmission is where diseases are spread through shared surfaces.

Question 18

What is direct transmission?

Answer 18

Direct transmission is where diseases are spread via exchanging bodily fluids and physical contact.

Question 19

What is tuberculosis?

Answer 19

Tuberculosis is a bacterial disease that infects animals. It is common in overcrowded places and is carried in the air (droplet transmission), or can be caught by eating or drinking produce from infected cattle. It causes appetite loss, fatigue, a productive cough, coughing blood, paleness and night sweats. It can be treated by taking antibiotics for months. 10% of those infected get ‘full blown TB’ which negatively impacts their ability to work.

Question 20

What is meningitis?

Answer 20

Meningitis is a bacterial disease that infects animals. It is spread via close contact and sharing bodily fluids. It causes a rash from sepsis and can be treated by taking a course of antibiotics. 25% people infected are left with permanent health issues and 10% die.

Question 21

What is ring rot?

Answer 21

Ring rot is a bacterial disease that infects tubers and fruit in plants. It is spread by contact of vegetables/plants and is spread through the soil. It causes damage to plants and there is no treatment but to leave fields infected clear of crop for two years, which negatively impacts farmers.

Question 22

What is HIV/AIDS?

Answer 22

AIDS is a viral disease caused by HIV that infects animals. It is spread through sexual contact/sharing bodily fluids. It targets t-helper cells so the body is less able to deal with other infections. It can be treated with retroviral drugs. In the last 10 years death from AIDS has decreased and in 2021 38.4 million people were infected.

Question 23

What is influenza?

Answer 23

Influenza is a viral disease that infects animals. It is spread via droplet transmission and touching infected surfaces. It causes respiratory issues, fever, headache, fatigue and pains. It can be treated/prevented with the flu vaccine. Avian flu is a strain that effects birds and can cause farmers to lose income.

Question 24

What is tobacco mosaic virus?

Answer 24

Tobacco mosaic virus is a viral disease that infects plants. It is spread via direct contact of plants, workers can also spread. It causes decolourisation/damage to leaves, flowers, fruit and may stunt growth. There is no treatment for TMV and it causes total crop loss for farmers.

Question 25

What is malaria?

Answer 25

Malaria is a protoctist disease that infects animals. It is spread through a vector (mosquitos, sharing needles). It causes lots of fever, headache, sweating, chills and vomiting. There is no treatment but anti-malarial drugs can be taken as a preventative. 50% of the world's population is in malaria risk areas, 627,000 deaths in one year.

Question 26

What is potato/tomato late blight?

Answer 26

Potato/tomato late blight is a protoctist disease that infects plants. It is spread through spores in the wind and infects all parts of the plant, hyphae from spores spread through tissue. It can be treated/prevented by using chemical sprays and choosing resistant species to plant. Impacts large crops and aided the Irish potato famine.

Question 27

What is black sigatota?

Answer 27

Black sigatota is a fungal disease that infects plants. It is spread through spores in the air or water. Hyphae from spores spread through roots and causes them to go black. Treatment is to use resistant bananas and use hangicides. It causes 50% less yield of bananas.

Question 28

What is ring worm?

Answer 28

Ring worm is a fungal disease that infects animals. It is spread by skin to skin contact and causes a raised, crusty scab. It is treated with anti-fungal cream and does not cause any lasting impact.

Question 29

What is athletes foot?

Answer 29

.

Question 30

How do plants recognise an attack by a disease?

Answer 30

Plants recognising an attack: - receptors respond to molecules from pathogens or chemicals released that attack the cell wall - the cells will then release signalling molecules - these switch on genes in the nucleus - this triggers cellular responses such as producing chemicals, sending alarm signals and strengthening the cell wall

Question 31

What physical defences do plants have against disease?

Answer 31

Physical defences: - cellulose cell wall = acts as a physical barriers and lignin thickens cell walls making them waterproof and indigestible - waxy cuticle = prevents water from collecting on the surface (pathogens need water) - guard cells = close stomata - callose = large polysaccharide that is deposited in sieve at the end of the growing season, blocks the flow so that pathogens can't spread

Question 32

What chemical defences do plants have against disease?

Answer 32

Chemical defences: - insect repellants = pine resin (antibacterial), citronella from lemongrass (masks attractive scents) - insecticides = pyrethins made by chrysanthemums and are a neurotoxin, caffeine which is toxic to insects and fungi by preventing enzymes that are required from working in an insects nervous system - antibacterial compounds including antibiotics = phenols (antiseptics made in many plants), antibacterial gossypol produced by cotton, defensins (proteins that disrupt bacterial and fungal membranes), lysosomes that break down bacterial cell walls - antifungal compounds = phenols, antifungal gossypol, defensins, saponins (chemicals in many cell membranes that interfere with fungal cell membranes), chitinases that break down chitin in fungal cell walls - anti-oomycetes = glucanases (enzymes that break down glucans (polymer in the cell walls of oomycetes/water moulds)) - general toxins = some plants make chemicals that can be broken down to form cyanide compounds when the plant cell is attacked

Question 33

Is callose made from alpha or beta glucose and which carbons would you find the bonds?

Answer 33

Callose is made from beta glucose and has 1,3 and 1,6 bonds.

Question 34

Initially callose is synthesised and deposited between the cell wall and cell membrane in cells next to infected cells. What is the purpose of this?

Answer 34

Callose is synthesised and deposited between the cell wall and cell membrane in cells next to infected cells to act as barriers and prevent pathogens entering the plam as around the site or infection.

Question 35

When is lignin added and what is it’s purpose (callose)?

Answer 35

Lignin is added when large amounts of callose is in the cell walls after the initial attack. This makes the mechanical barrier to invasion even thicker and stronger.

Question 36

What is the purpose of callose in plasmodesmata?

Answer 36

Callose in plasmodesmata is deposited between infected cells and neighbours, sealing them off from healthy cells and helps prevent pathogens from spreading.

Question 37

What is the purpose of callose in the phloem vessels?

Answer 37

Callose in the phloem vessels blocks the sieve plates of the phloem, sealing off infection and preventing the spread.

Question 38

What are the types of human defences against disease?

Answer 38

Human defences against disease: - non-specific defences (innate immunity) = primary defences or primary responses - specific defences (acquired immunity) = through cell-mediated immunity or humeral immunity

Question 39

What is the purpose of the primary defence skin?

Answer 39

Skin: - protective barrier that covers the whole body - skin flora that outcompetes pathogens for space - produces sebum that inhibits the growth of pathogens

Question 40

What is the purpose of the primary defence mucus?

Answer 40

Mucus: - many of the tracts in the body (e.g respiratory reacts) are lined by mucus membranes which secrete mucus - traps microorganisms - contains lysosomes which destroy cell walls - contains phagocytes - coughs and sneezes also eject pathogen-laden mucus

Question 41

How does the primary response of blood clotting work?

Answer 41

Blood clotting: - platelets secrete several substances when they come into contact with collagen in the skin = thromboplastin = serotonin - a scab forms and epidermal cells begin to grow underneath, eventually sealing the wound permanently = collagen strengthens the tissue

Question 42

What is the process of blood clotting?

Answer 42

Blood clotting process: 1. injured tissues and platelets release the clotting factor prothrombin activator and calcium ions 2. prothrombin activator converts the blood protein prothrombin to thrombin 3. thrombin splits fibrinogen to form fibrin 4. fibrin fibres form a mesh over wounds trapping red blood cells and platelets 5. bleeding stops 6. clots harden and become smaller 7. new cells grow to repair wound site 8. enzyme plasmin released to dissolve clot

Question 43

How does the primary inflammatory response work?

Answer 43

Inflammatory response: -localised response causing pain, heat, redness and swelling that is brought about by signalling molecules - mast cells (a type of white blood cell) release histamines and cytokines - histamines cause nearby blood vessels to dilate and become more permeable - cytokines attract phagocytes to the side

Question 44

What is the primary response of fever?

Answer 44

Fever: - normal body temperature is 37°c and is maintained by the hypothalamus - pathogens reproduce optimally at this or below this temperature - pathogens trigger cytokines to send a signal to hypothalamus to increase this temperature to inhibit pathogen reproduction and to allow specific immune system to work more effectively

Question 45

What are the types of phagocytosis?

Answer 45

The types of phagocytosis is neutrophilic phagocytosis and macrophage phagocytosis.

Question 46

What is the process of neutrophilic phagocytosis?

Answer 46

Neutrophilic phagocytosis: 1. pathogens produce chemicals (or are tagged by opsonins) that attract phagocytes 2. phagocytes recognise non-human proteins on the pathogen (antigens)- not specific to a type of pathogen 3. engulfs the pathogen and encloses it in a vacuole called a phagosome 4. combines with a lysosome to form a phagosome 5. enzymes from the lysosome digest and destroy the pathogen, releasing debris by exocytosis

Question 47

What is the process of macrophage phagocytosis?

Answer 47

Macrophage phagocytosis: - 1-4 same as neutrophilic phagocytosis 5. rather than releasing debris, carbohydrates are added to the antigen to form a major histocompatibility complex (MHC) 6. this is then placed on the surface of the macrophage forming an antigen presenting cell (APC)

Question 48

What are cytokines?

Answer 48

Cytokines are helpful chemicals. - cell signalling molecules - inform the phagocytes that the body is under attack and stimulate them to move to the site of infection/inflammation - cytokines increase body temperature and can also stimulate the specific immune system

Question 49

What are opsonins?

Answer 49

Opsonins are helpful chemicals. - chemicals that bind to pathogens (can be antibodies) and tag them so that they can be recognised by phagocytes - phagocytes have receptors that bind to common opsonins and the phagocyte then engulfs the pathogen

Question 50

What are lymphocytes?

Answer 50

Lymphocytes: - specialised white blood cells that are involved in the specific immune response - much smaller than phagocytes - both types of lymphocyte originate in the bone marrow and differentiate from haematopietic stem cells - b-lymphocytes mature in the bone marrow and t-lymphocytes mature in the thymus gland

Question 51

What is clonal selection?

Answer 51

Clonal selection is when exposure to a specific antigen selectively stimulates the proliferation or the cell within the appropriate antibody to form numerous clones of the specific andibody forming cells.

Question 52

What is clonal expansion?

Answer 52

Clonal expansion is the mass proliferation or antibody producing cells by clonal selection.

Question 53

What is cell mediated immunity?

Answer 53

Cell mediated immunity is the immune response mediated by activaling t-helper cells, than then lead to the other b and t cells being activated and propagated.

Question 54

What are t-helper cells?

Answer 54

T-helper cells: - have cell receptors on their cell membrane that allows them to bind to the specific antigens on the surface of an APC (macrophage) = clonal selection - this triggers the specific immune response by producing cytokines (specifically called interleukins) = cell mediated response

Question 55

What are t-killer cells?

Answer 55

T-killer cells: - destroy the pathogen (or human infected cell) carrying the antigen - produce the chemical perforin - perforin makes holes in the cell membrane (by releasing porin proteins) of the infected cell, making it freely permeable

Question 56

What are t-regulator cells?

Answer 56

T-regulator cells: - prevent an autoimmune response attack on own healthy bodily cells - makes sure the body recognises ‘self antigens’ - stops the immune response once the pathogen has been eliminated

Question 57

What are t-memory cells?

Answer 57

T-memory cells: - live for a long time and are part of immunological memory - if they meet an antigen for a second time (secondary exposure) they divide rapidly to form clones of t-killer cells to destroy the pathogen (done without the need to go through the clonal selection stage)

Question 58

What is humoral immunity?

Answer 58

Humoral immunity is the immune response where the body responds to antigens found outside of cells, by producing soluble antibodies transported in the blood/tissue fluid. - the b-cell that is specific to the antigen is activated by the t-helper cell = clonal selection - t-helper cell releases interleukins that stimulate the selected b-cell to divide by mitosis (clonal expansion) - b-cells then differentiate into plasma cells, b-effector cells or b-memory cells

Question 59

What are the types of lymphocyte?

Answer 59

Lymphocytes are split into t-lymphocytes and b-lymphocytes. T-lymphocytes include t-helper cells, t-killer cells, t-receptor cells and t-memory cells. B-lymphocytes include plasma cells, b-effector cells and b-memory cells.

Question 60

What is the primary response once the body has been exposed to disease?

Answer 60

Primary response: - takes time to find the pathogen and for lymphocytes to replicate enough to produce antibodies, therefore symptoms will occur - if survived, b-memory and t-memory cells will have immunological memory

Question 61

What is the secondary response once the body has been exposed to disease?

Answer 61

Secondary response: - b-memory cells divide rapidly to form plasma cell clones so the correct antibody is produced quickly with no symptoms.

Question 62

What is an antigen?

Answer 62

An antigen is an identifying chemical on the surface of a molecule that triggers an immune response.

Question 63

What is an antibody?

Answer 63

Antibodies are Y shaped glycoproteins made by B cells of the immune system in response to the presence of a specific antigen.

Question 64

What is the immune response?

Answer 64

The immune response is the biological response that protects the body by recognising and responding to antigens and destroying substances carrying non-self antigens.

Question 65

What does it mean to be immune?

Answer 65

Immune is when you have protection against infectious diseases which is gained actively or passively.

Question 66

What are the parts of an antibody?

Answer 66

Parts of an antibody: - antigen binding site - variable region - disulphide bridge - light polypeptide chain - heavy polypeptide chain - constant region - receptor binding site

Question 67

What do antibodies do?

Answer 67

Antibodies: - produced by plasma cells - y-shaped glycoproteins and immunoglobulins - bind to specific antigens so have a specific shape - have complimentary shape to the antigen

Question 68

How to antibodies inactivate antigens?

Answer 68

Antibodies inactivate antigens by: - stop them invading cells by neutralisation (e.g blocking binding sites/forming antigen-antibody complexes) - agglutination of microbes = causing many antigen-antibody complexes to be formed to prevent their spread of the pathogen - antibody acts as an opsonin so that phagocytes can locate it easily - act as antitoxins, deactivating their harmful nature

Question 69

What is an autoimmune disease?

Answer 69

An autoimmune disease is a condition or illness resulting from an autoimmune response. - where the body cannot differentiate own healthy cells from pathogens and stops recognising ‘self’ cells and attacks healthy tissue

Question 70

What is type I diabetes?

Answer 70

Type I diabetes is an autoimmune disease where the insulin secreting cells of the pancreas are attacked. It causes thirst, fatigue, weight loss, slow healing cuts, bruises, blurred vision and thrush. It can be treated with insulin injections, pancreas transplants and autoimmune drugs.

Question 71

What is rheumatoid arthritis?

Answer 71

Rheumatoid arthritis is an autoimmune disease where the joints are effected. It causes joint pain and stiffness and inflammation around the joints. There is no cure but it can be treated with steroids, anti-inflammatory drugs and painkillers.

Question 72

What is lupus?

Answer 72

Lupus is an autoimmune disease that effects the skin and joints but can attack any organ in the body (including the kidneys, lungs, liver and brain). It causes rashes, fatigue and joint and muscle pain. There is no cure but it can be treated with steroids, anti-inflammatory drugs and immunosuppressants.

Question 73

What is Addison’s disease?

Answer 73

Addison’s disease is an autoimmune disease which attacks the adrenal gland. It causes fatigue, weak muscles, low mood, weight loss and thirst. It can be treated via steroid replacement therapy.

Question 74

What is sjogren’s disease?

Answer 74

Sjogren’s disease is an autoimmune disease that attacks the lungs, kidneys and nervous system. It causes dry eyes, dry mouth, dry skin, fatigue, pain, rashes and swelling. There is no cure but it can be treated with eye drops, sprays and medicine to produce tears and saliva.

Question 75

What is a vaccination?

Answer 75

A vaccination is a method artificially activating the immune system to produce antibodies.

Question 76

What could a vaccine contain?

Answer 76

A vaccine could contain: - whole live organisms (e.g small pox) - dead or inactive bacteria or viruses (e.g whooping cough) - attenuated versions (e.g measles) - harmless toxins (e.g tetanus) - antigens that have been extracted (e.g flu) - genetically engineered antigens (e.g hepatitis b) - genetically engineered RNA (e.g HIV, COVID)

Question 77

Why was the smallpox vaccine successful?

Answer 77

Smallpox was eradicated in 1979 after a successful vaccination programme. The vaccine was so effective because: - it was a stable pathogen (did not mature) - it was a live vaccine - easy and cheap to produce (highly available) - easy to store (heat durable and freeze-dried) - easy to identify infected patients - easy to administer with no booster required - only hosted by humans (not zoonotic)

Question 78

What is the difference between active and passive immunity?

Answer 78

Active immunity is the production of own antibodies, passive immunity does not produce own antibodies.

Question 79

What is active natural immunity and active artificial immunity?

Answer 79

Active natural immunity is antibodies developed in response to infection. Active artificial immunity is antibodies acquired via vaccination.

Question 80

What is passive natural immunity and passive artificial immunity?

Answer 80

Passive natural immunity is antibodies received via mothers breast milk. Passive artificial immunity is antibodies received via medicine infusion or y-globulin injection.

Question 81

What are the advantages and disadvantages of active natural immunity?

Answer 81

Active natural immunity advantages: - can immediately destroy pathogens - long-term immunity - produces antibodies/memory cells Active natural immunity disadvantages: - immune response takes time - symptoms may develop - disease may be fast and fatal

Question 82

What are the advantages and disadvantages of active artificial immunity?

Answer 82

Active artificial immunity advantages: - stimulates body to make own antibodies - long-term immunity - no need to suffer Active artificial immunity disadvantages: - could cause the disease and have fatal results - boosters required - may react to vaccine - takes time

Question 83

What are the advantages and disadvantages of passive natural immunity?

Answer 83

Passive natural immunity advantages: - lasts until immune system of babies can make own antibodies - immediate protection Passive natural immunity disadvantages: - short-term - no memory cells produced

Question 84

What are the advantages and disadvantages of passive artificial immunity?

Answer 84

Passive artificial immunity advantages: - can be lifesaving - immediate protection against a specific disease Passive artificial immunity disadvantages: - doesn’t last long - no memory cells produced - may react to vaccine

Question 85

What is herd vaccination?

Answer 85

Herd vaccination is where all/most of the population is vaccinated to stop the spread of a disease (e.g COVID, small pox).

Question 86

What is ring vaccination?

Answer 86

Ring vaccination is where people around the victim of a disease are vaccinated to prevent transmission (e.g meningitis).

Question 87

What are the problems with vaccines?

Answer 87

Problems with vaccines: - people resistant to vaccination - allergies to vaccine - virus mutates, needs boosters - herd immunity needs mass production, expensive transport and storage - some may to need more than one vaccination - chance of contracting virus arter vaccination - close correlation between the incidence of one disease and another (e.g AIDS and TB). - multiple strains or pathogen - animal vectors, multiple host species - species presenting multiple different antigens - delivery method = oral or injection - genetic disorders caused by pathogens

Question 88

Why do we need new medicines?

Answer 88

Why we need new medicines: - pathogens become resistant to existing drugs (e.g antibiotics) - new diseases emerge - new vaccines needed (e.g HIV) - existing vaccines can be improved

Question 89

How are new medicines discovered?

Answer 89

New medicines discovered: - by accident (e.g fleming and penicillin) - traditional medicine - anaesthetics - modern research (e.g analysing genomes of pathogens, computer modelling of potential drugs)

Question 90

What are the sources of some medicines?

Answer 90

Sources of medicines: - digoxin (from foxgloves) = heart drug for atrial fibrillation and heart failure = improves filling time of heart and coronary circulation - diamorphine (from opium poppy) = painkillers include codeine and morphine - amica (from amica flowers) = used to reduce bruising - taxol (from yew tree) = cancer drug - prialt (from cone snail) = painkiller, 1000x times more effective than morphine

Question 91

What is bioprospecting?

Answer 91

Bioprospecting is where scientists look for new medicines among living organisms, involves observations.

Question 92

What are the drugs for the future?

Answer 92

Drugs for the future: - pharmacogenetics = using information from the genome to personalise medicine that will work with the individuals genetics and disease - synthetic biology = creating genetically modified organisms that produce drugs - nanotechnology = nano particles used to deliver drugs to sites within ums