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[h] IB DP Biology HL C3.2 Defence against disease Flashcards
[q] C3.2.1—Pathogens as the cause of infectious diseases
[a] Students should understand that a broad range of disease-causing organisms can infect humans.
A disease-causing organism is known as a pathogen, although typically the term is reserved for viruses, bacteria, fungi and protists.
Archaea are not known to cause any diseases in humans.
NOS: Students should be aware that careful observation can lead to important progress.
For example, careful observations during 19th-century epidemics of childbed fever (due to an infection after childbirth) in Vienna and cholera in London led to breakthroughs in the control of infectious disease.
[q] C3.2.2—Skin and mucous membranes as a primary defence
[a] The skin acts as both a physical and chemical barrier to pathogens.
Students are not required to draw or label diagrams of skin.
[q] C3.2.3—Sealing of cuts in skin by blood clotting
[a] Include release of clotting factors from platelets and the subsequent cascade pathway that results in rapid conversion of fibrinogen to fibrin by thrombin and trapping of erythrocytes to form a clot.
No further details are required.
[q] C3.2.4—Differences between the innate immune system and the adaptive immune system
[a] Include the idea that the innate system responds to broad categories of pathogen and does not change during an organism’s life whereas the adaptive system responds in a specific way to particular pathogens and builds up a memory of pathogens encountered, so the immune response becomes more effective.
Students are not required to know any components of the innate immune system other than phagocytes.
[q] C3.2.5—Infection control by phagocytes
[a] Include amoeboid movement from blood to sites of infection, where phagocytes recognize pathogens, engulf them by endocytosis and digest them using enzymes from lysosomes.
[q] C3.2.6—Lymphocytes as cells in the adaptive immune system that cooperate to produce antibodies
[a] Students should understand that lymphocytes both circulate in the blood and are contained in lymph nodes.
They should appreciate that an individual has a very large number of B-lymphocytes that each make a specific type of antibody.
[q] C3.2.7—Antigens as recognition molecules that trigger antibody production
[a] Students should appreciate that most antigens are glycoproteins or other proteins and that they are usually located on the outer surfaces of pathogens.
Antigens on the surface of erythrocytes may stimulate antibody production if transfused into a person with a different blood group.
[q] C3.2.8—Activation of B-lymphocytes by helper T-lymphocytes
[a] Students should understand that there are antigen-specific B-cells and helper T-cells.
B-cells produce antibodies and become memory cells only when they have been activated.
Activation requires both direct interaction with the specific antigen and contact with a helper T-cell that has also become activated by the same type of antigen.
[q] C3.2.9—Multiplication of activated B-lymphocytes to form clones of antibody-secreting plasma cells
[a] There are relatively small numbers of B-cells that respond to a specific antigen.
To produce sufficient quantities of antibody, activated B-cells first divide by mitosis to produce large numbers of plasma B-cells that are capable of producing the same type of antibody.
[q] C3.2.10—Immunity as a consequence of retaining memory cells
[a] Students should understand that immunity is the ability to eliminate an infectious disease from the body.
It is due to the long-term survival of lymphocytes that are capable of making the specific antibodies needed to fight the infection.
These are memory cells.
[q] C3.2.11—Transmission of HIV in body fluids
[a] Include examples of the mechanisms of HIV (human immunodeficiency virus) transmission.
[q] C3.2.12—Infection of lymphocytes by HIV with AIDS as a consequence
[a] Students should understand that only certain types of lymphocyte are infected and killed, but that a reduction in these lymphocytes limits the ability to produce antibodies and fight opportunistic infections.
[q] C3.2.13—Antibiotics as chemicals that block processes occurring in bacteria but not in eukaryotic cells
[a] Include reasons that antibiotics fail to control infection with viruses.
[q] C3.2.14—Evolution of resistance to several antibiotics in strains of pathogenic bacteria
[a] Students should understand that careful use of antibiotics is necessary to slow the emergence of Multi resistant bacteria.
NOS: Students should recognize that the development of new techniques can lead to new avenues of research; for example, the recent technique of searching chemical libraries is yielding new antibiotics.
[q] C3.2.15—Zoonoses as infectious diseases that can transfer from other species to humans
[a] Illustrate the prevalence of zoonoses as infectious diseases in humans and their varied modes of infection with several examples including tuberculosis, rabies and Japanese encephalitis.
Include COVID-19 as an infectious disease that has recently transferred from another species, with profound consequences for humans.
[q] C3.2.16—Vaccines and immunization
[a] Students should understand that vaccines contain antigens, or nucleic acids (DNA or RNA) with sequences that code for antigens, and that they stimulate the development of immunity to a specific pathogen without causing the disease.
[q] C3.2.17—Herd immunity and the prevention of epidemics
[a] Students should understand how members of a population are interdependent in building herd immunity.
If a sufficient percentage of a population is immune to a disease, transmission is greatly impeded.
NOS: Scientists publish their research so that other scientists can evaluate it.
The media often report on the research while evaluation is still happening, and consumers need to be aware of this.
Vaccines are tested rigorously, and the risks of side effects are minimal but not nil.
The distinction between pragmatic truths and certainty is poorly understood.
[q] C3.2.18—Evaluation of data related to the COVID-19 pandemic
[a] Application of skills: Students should have the opportunity to calculate both percentage difference and percentage change.
[q] Disease
[a] Type of illness w/ characteristic symptoms
[q] Causes
[a] 1. Genetic – genetic disorders
2. environmental – toxins/radiation
3. Pathogens – organisms and viruses
4. Prion – Proteins that cause other proteins to misfold
[q] Pathogens
[a] Microorganisms that pass from one infected organism to another, they enter, multiply, and cause harm
[q] Pathogen Types
[a] 1. Bacteria – tuberculosis, leprosy
2. Fungi – athlete’s foot
3. Protista (single-celled prokaryote) – malaria, sleeping sickness
4. Viruses (non-living) – influenza, measles, Ebola
[q] First Line of Defense
[a] include skin and mucus membranes
[q] Skin
[a] physical barrier that keeps pathogens out, layer of dry/thick/dead cells containing keratin
[q] Sebaceous Glands
[a] secrete lactic acid to make skin slightly acidic and inhibit microbial growth
[q] Mucus Membranes
[a] protect internal structures (ex. esophagus, trachea, genitals)
they are ciliated and secrete mucus (to trap and swallow/expel)
[q] Ciliated
[a] property of mucus membranes, have little cilia to move stuff and remove pathogens via coughing
[q] Lysozyme
[a] mucus membrane contains these, they are antiseptic that causes lysis in bacteria cell walls
[q] Blood Clotting (hemostasis)
[a] repairs damaged blood vessels in a cut, prevents blood loss and limits pathogen entry
[q] Platelets
[a] First step of blood clotting, they are blood cell fragments that change structurally to form a temporary “plug” of sticky, semi-solid gel
*They release clotting factors that eventually form insoluble mesh (scab)*
[q] Coagulation Cascade Process
[a] 1. inactive prothrombin becomes active thrombin
2. thrombin converts soluble fibrinogen to insoluble fibrin
3. fibrin forms a blood clot that traps cells and seals wound
4. when exposed to air, blood clot forms a scab
5. after damage repaired, plasmin dissolves clot and scab
[q] Leukocytes
[a] white blood cells
[q] Second Line of Defense
[a] Non-specific – responds to broad array of pathogens
Non-adaptive – responds in the same way, every time
[q] Phagocytes
[a] type of leukocyte that patrols blood and eats pathogens via endocytosis
ex. macrophage
[q] Endocytosis
[a] process by which a cell takes material into the cell by infoldings of the cell membrane
[q] Histamine
[a] a compound that is released by cells in response to injury and in allergic and inflammatory reactions, causing contraction of smooth muscle and dilation of capillaries.
[q] Chemotaxis
[a] movement by a cell or organism in reaction to a chemical stimulus
[q] Second Line of Defense Process
[a] 1. Phagocyte’s pseudopodia engulf pathogens
2. traps pathogens in vesicles
3. Fuses vesicle w/ lysosomes to form phagolysosomes (dissolves bacteria)
4. presents antigens (fragments of pathogen) on surface to initiate 3rd line of defense
[q] Pseudopodia
[a] part of phagocytes that helps to entrap pathogen
[q] Phagolysosome
[a] fusion of vesicle w/ pathogen and lysosome, allows of pathogen destruction
[q] 3rd Line of Defense
[a] Specific – differentiates between pathogens and alters response
Adaptive – builds memory to respond faster to same pathogen
*lymphocytes*
[q] Lymphatic System
[a] where white blood cells travel, consists of nodes and vessels
Function: manage fluid levels in body, returns fluid (lymph) leaked from circulatory system back to it via nodes
[q] Antigen vs. Antibody
[a] Antigen: “them”
-glycoproteins found on pathogen/cell surface, elicits immune response (antibody production)
Antibodies: “us”
-protein made by lymphocytes
-complimentary in shape and charge to antigens
-binding between the two is irreversible
[q] More on Antibodies
[a] -produced by lymphocytes, each lymphocyte can only produce one type (b/c clone)
-made up of 4 polypeptides
-makes pathogen more recognizable to phagocytes
-prevents viruses from docking to host cells
[q] Opsonization
[a] An immune response in which the binding of antibodies to the surface of a microbe facilitates phagocytosis of the microbe by a macrophage
[q] Opsonin
[a] an antibody or other substance that binds to foreign microorganisms or cells, making them more susceptible to phagocytosis.
[q] Antibody Regions
[a] Hypervariable: binding site of antigens from phagocytes or pathogens or random antigens floating around Constant: helps body fight pathogen (able to be recognized by B-cell)
[q] Types of Lymphocytes
[a] 1. B-cells, made in bone marrow, produces antibodies
2. Helper T-cells, matures in Thymus, activates B-cells and cytotoxic T-cells
3. Cytotoxic T-cells, destroys body’s own cells that have been infected or become cancerous
[q] After Antigen Presentation in Phagocytes…
[a] antigens bind to and activate specific helper-t cells that have complimentary antigen receptors activated helper t-cells then activate helper specific B-cells
[q] How do Helper T-cells activate B-cells?
[a] By releasing cytokines or through direct contact
[q] Cytokines
[a] type of ligand released by Helper-T cell to activate B-cell
[q] Activated B-cell Differentiation
[a] Plasma B-Cells or Memory B-cells
[q] Effector Cell
[a] A short-lived cell, what a Plasma B-cell is
[q] Plasma B-cell
[a] A short lived cell that produces high amounts of specific antibodies
They develop extensive rER and Golgi to assist in protein synthesis
*die after infection overcome*
[q] Memory B-cells
[a] Remain inactive until same pathogen enters system, then activate and respond rapidly by stimulating production of Plasma B-cells
[q] Immunity
[a] Either having antibodies to pathogen or memory B-cells that can rapidly produce antibodies
[q] Cytotoxic T-cells
[a] destroy pathogens and body’s own infected cells by secreting perforating proteins to puncture cell membrane and induce cell lysis
[q] Antibody Relevance in pathogen removal
[a] Produced by plasma b-cells, then tag antigens of pathogens by binding to it with hypervariable region. Constant region then attracts macrophages (phagocytes) for pathogen destruction
[q] HIV Transmission
[a] Occurs via exchange of body fluids
1. unprotected sex w/ abrasions
2. shared usage of hypodermic needles
3. blood transfusions or blood products
4. childbirth and breastfeeding
[q] HIV (General Facts)
[a] A RNA retrovirus that synthesizes DNA with reverse transcriptase
[q] How to inhibit HIV
[a] 1. Use antiretroviral drugs to inhibit reverse transcriptase
2. Use drugs that target HIV enzymes utilizes in DNA entry
[q] How HIV affects the immune system
[a] It destroys Helper T-cells, meaning that the CD4+ receptor can no longer recognize antigens on pathogens.
Therefore, no activated B-cells (no antibodies) or no activated cytotoxic T-cells Host eventually killed by opportunistic infections (because can no longer respond normal infections w/ 3rd line of defense)
[q] AIDS
[a] Acquired Immunodeficiency Syndrome
Syndrome is a collection of symptoms and infections
Kaposi’s Sarcoma, a marker disease (if u have Kaposi’s Sarcoma, then u likely have HIV)
[q] Bactericidal vs. Bacteriostatic
[a] Bactericidal – Kills bacteria
Bacteriostatic – Inhibits bacterial growth
[q] Antibiotics
[a] Kill and/or inhibit growth of bacteria
Target prokaryotic DNA replication, protein synthesis, enzymes, 70S ribosomes, and cell wall formation
*don’t affect eukaryotes because of structural and metabolic differences*
*don’t affect viruses because viruses are non-living and have no metabolism*
[q] Narrow vs Broad Spectrum
[a] Narrow Spectrum – effective against specific bacteria
Broad Spectrum – effective against many types of bacteria
[q] Fleming (1928)
[a] Identified penicillin, first chemical antibiotic
[q] Penicillin
[a] Produced by saprotrophic fungi that competed with saprotrophic bacteria, inhibits bacterial competitors via secretion
[q] Florey and Chain (1940)
[a] first clinical trials of penicillin
[q] Antibiotic Resistance
[a] Only a concern if strains with multiple resistances develop (such things are now widespread.
Easy for bacteria to get because of horizontal gene transfer using plasmids (can just transfer resistance gene)
[q] MRSA
[a] Methicillin-resistant Staphylococcus aureus)
Example of strain with multiple resistances
**superbacteria**
[q] Measures to Prevent Antibiotic Resistance
[a] 1. Prescribe antibiotics for only serios bacteria
2. Maintain high level of hygiene to prevent cross infection
3. Farmers must exclude antibiotics from animal feeds
4. Develop new antibiotics
5. Do not overuse antibiotic products
[q] Zoonoses
[a] Type of pathogen that can cross from species (zoonotic pathogen)
*Most pathogens species specific*
[q] Zoonoses Examples
[a] Mycobacterium Bovis (cows)
Lyssaviruses (rabies)
COVID-19 (bats)
[q] Immunity Xtra Info
[a] Having Memory B-cells that, if second infection, can quickly produce plasma B-cells to produce antibodies Prevents disease from really developing
[q] Vaccinations
[a] Promotes immunity by producing memory B-cells given via intramuscular or subcutaneous (skin) injections Contains some form of pathogen (weakened/killed pathogen, subunits of pathogen like antigen, or mRNA that codes for antigen)
[q] Epidemic
[a] increase in prevalence of infection within a region
[q] Pandemic
[a] Epidemic that has spread over a larger area
[q] Herd Immunity
[a] Spread of pathogen is impeded because of its repeated encounters with people who are immune, can protect individuals that cannot be vaccinated.
Created via vaccination or those who have already had the disease
[q] Herd Immunity Equation
[a] (1-1/r) * 100%
R is the average number of people that the infected person infects
[q] Cause of infectious diseases
[a] A disease-causing organism is known as a pathogen, although typically the term is reserved for viruses, bacteria, fungi and protists.
Archaea are not known to cause any diseases in humans.
[q] Primary defence
[a] Skin and mucous membranes act as the primary defence.
The skin acts as both a physical and chemical barrier to pathogens.
[q] Sealing of cuts in skin by blood clotting
[a] Release of clotting factors from platelets and the subsequent cascade pathway that results in rapid conversion of fibrinogen to fibrin by thrombin and trapping of erythrocytes to form a clot.
[q] Differences between the innate immune system and the adaptive immune system
[a] The idea that the innate system responds to broad categories of pathogens and does not change during an organism’s life whereas the adaptive system responds in a specific way to particular pathogens and builds up a memory of pathogens encountered, so the immune response becomes more effective.
[q] Infection control by phagocytes
[a] Amoeboid movement from blood to sites of infection, where phagocytes recognize pathogens, engulf them by endocytosis and digest them using enzymes from lysosomes.
[q] Lymphocytes
[a] Lymphocytes both circulate in the blood and are contained in lymph nodes. An individual has a very large number of B-lymphocytes that each make a specific type of antibody.
[q] Antigens
[a] Most antigens are glycoproteins or other proteins and that they are usually located on the outer surfaces of pathogens.
Antigens on the surface of erythrocytes may stimulate antibody production if transfused into a person with a different blood group.
[q] Activation of B-lymphocytes by helper T-lymphocytes
[a] There are antigen-specific B-cells and helper T-cells.
B-cells produce antibodies and become memory cells only when they have been activated.
Activation requires both direct interaction with the specific antigen and contact with a helper T-cell that has also become activated by the same type of antigen.
[q] Multiplication of activated B-lymphocytes
[a] There are relatively small numbers of B-cells that respond to a specific antigen.
To produce sufficient quantities of antibody, activated B-cells first divide by mitosis to produce large numbers of plasma B-cells that are capable of producing the same type of antibody.
[q] Immunity
[a] Immunity is the ability to eliminate an infectious disease from the body.
It is due to the long-term survival of lymphocytes that are capable of making the specific antibodies needed to fight the infection.
These are memory cells.
[q] Transmission of HIV in body fluids
[a] HIV is transmitted through infected vaginal fluids or semen, blood and breastmilk.
The use of adequate protection by medical professionals when handling the body fluids of infected patients is important as the virus can be spread through the exposure of broken skin to infected blood
[q] Infection of lymphocytes by HIV with AIDS as a consequence
[a] Only certain types of lymphocytes are infected and killed, but that a reduction in these lymphocytes limits the ability to produce antibodies and fight opportunistic infections.
[q] Antibiotics as chemicals that block processes occurring in bacteria but not in eukaryotic cells
[a] Antibiotics fail against viral infections because they target bacteria, not viruses.
Viruses replicate inside host cells, making it difficult to develop drugs that specifically target them without harming the host.
Antiviral drugs are specific to certain viruses, and viral mutation can lead to drug resistance.
[q] Evolution of resistance to several antibiotics in strains of pathogenic bacteria
[a] Careful use of antibiotics is necessary to slow the emergence of multiresistant bacteria.
[q] Zoonoses as infectious diseases that can transfer from other species to humans
[a] Zoonotic diseases, like tuberculosis, rabies, Japanese encephalitis, and COVID-19, demonstrate the prevalence of infections that transfer from animals to humans.
They can be transmitted through various means such as inhalation, bites, and vectors like mosquitoes.
COVID-19, in particular, has shown the profound consequences of a recent zoonotic transfer.
[q] Vaccines and immunization
[a] Vaccines contain antigens, or nucleic acids (DNA or RNA) with sequences that code for antigens, and that they stimulate the development of immunity to a specific pathogen without causing the disease.
[q] Herd immunity and the prevention of epidemics
[a] If a sufficient percentage of a population is immune to a disease, transmission is greatly impeded.
Minimum 80% of the population needs to be vaccinated to achieve herd immunity.
[q] Percentage difference and percentage change
[a] Percentage difference: dividing the absolute value of the change by the average of the values and multiplying by 100.
Percentage change: find the difference between the original and new values.
Divide the difference by the original value.
Multiply the resulting quotient by 100.
A disease-causing organism is known as a pathogen, although typically the term is reserved for viruses, bacteria, fungi and protists.
Pathogens are diverse agents and microorganisms that cause disease in their host (the organism being infected).
• ability to colonize the host
• use host resources to replicate
• circumvent, avoid, or subvert the host’s immune responses
• find a niche that is nutritionally compatible in the host
• spread to a new host
Archaea are a domain of unicellular organisms, and are (so far) not known to cause any disease in humans.
Ignaz Semmelweis, a Hungarian physician, observed that physicians who examined cadavers and then immediately after assisted in the birth of a child had higher frequences of childbed fever fatalities compared to midwives, who did not examine cadavers.
Main idea: both scientists observed data about where fatality rates are highest and identified potential causes, enabling the development of infection control methods.
The innate immune system is composed of the first and second lines of defence, with the adaptive immune system being the third line of defence.
The skin and mucous membranes act as a primary defence due to (TACID):
• tears and mucous trap and rinse pathogens away
• skin’s acidity increases difficulty of pathogen survival
• competition of pathogen with normal flora reduces its survivability
• acting as a continuous, impermeable barrier to pathogens
• killing or deactivating pathogens by desiccation (drying out)
1. release of clotting factors from platelets and damaged cells
2. conversion of prothrombin (inactive) to thrombin (active form)
3. conversion of fibrinogen (soluble) into fibrin (insoluble) by thrombin
Insoluble fibrin forms a mesh around the site of injury, trapping erythrocytes (red blood cells) to form a clot.
This helps to restore a temporary physical barrier until the skin and surrounding tissue heal.
A phagocyte (also called macrophage) is a white blood cell (leukocyte) that performs phagocytosis.
To reach the site of infection, phagocytes are characterized by movement that resembles that of amoeba (amoeboid movement).
There are around 2 × 10!” lymphocytes in the human body, comparable in cell mass to the brain or liver.
Each B-lymphocyte produces a specific antibody (immunoglobin), which is any group of proteins that binds to an antigen.
• Complement activation: the complement system is a large number of proteins that work to fight off disease by opsonization and cell lysis – it ‘complements’ the work of antibodies.
• Opsonization: the antibody binds to the pathogen’s antigens to promote phagocytosis and make it easier for phagocytes to identify and engulf the pathogen.
• Neutralization: the antibody prevents the pathogen from adhering to host cells, reducing its ability to cause damage.
Heteroantigens are any antigen derived from one species (pathogen) that is able to stimulate an immune response in another species (host).
The ABO blood group system is the classification of human blood based on absence or presence of antigens A or B.
Plasma cells are differentiated B-cells capable of producing one type of antibody that is specific to the antigen presented by T-cells.
These cells do not produce antibodies during the first exposure, but can immediately start producing upon a second infection or exposure.
The Human Immunodeficiency Virus (HIV) is a major global health issue, transmitted by:
• bodily fluids of an infected person, including breast milk, blood, vaginal fluids, and semen
• a pregnant woman to her baby
• contaminated needles and other injecting equipment for drugs
• unsafe blood transfusions, injections, tissue transplantation, and unsterile medical procedures
HIV is not transmitted through ordinary contacts such as sharing a glass, coughing, sneezing, or kissing.
Acquired Immunodeficiency Syndrome (AIDS) is the last and most serious stage of an infection with HIV, and occurs when the individual’s immunity is so weak that other pathogens start causing illnesses that would normally not occur in a healthy person.
Since viruses are not considered ‘living,’ antibiotics are not an option for controlling viral infections.
• inappropriate prescription of antibiotics to patients
• overuse in hospitals and agriculture
• reduced availability of new antibiotics due to high research expenses
This is alarming because the world could return to the ‘pre-antibiotic era’ of high mortality rates.
• Tuberculosis (TB) is a bacterium mainly transmitted by cattle to humans by drinking their contaminated milk or inhaling their sneeze or cough droplets.
• Rabies is a viral disease mainly transmitted by dog bites and affects the central nervous system.
• Japanese encephalitis is a viral disease transmitted through mosquito bites.
• COVID-19 is a viral disease that is accepted to have been transmitted from bats, causing a worldwide pandemic and lockdown for more than a year
• an attenuated version of the pathogen
• a killed version of the pathogen
• fragments of the pathogens (i.e. its antigens)
• mRNA that codes for the pathogen’s antigens, stimulating antibody production in the vaccinated person
Misinformation on new scientific phenomena can become widespread, so critical evaluation of sources is needed by the public in order to validate pragmatic truths.
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