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Biology U3/4 > Chapter 5: Responding to Antigens and Acquiring Immunity > Flashcards

Chapter 5: Responding to Antigens and Acquiring Immunity Flashcards

1
Q

Define antigen

A
  • Antigens are molecules or parts of molecules that stimulate an immune response
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2
Q

Describe the difference between self and non-self antigens

A
  • Self antigens are antigens on cells that are recognised by self-receptors as being part of the same body
  • Non-self antigens are antigens that do not belong to the body’s own cells
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3
Q

Describe the difference between MHC-I and MHC-II self markers

A
  • MHC-I is a type of major histocompatibility complex found on all nucleated cells
    • They allow cells to be recognised as “self”
  • MHC-II is a type of major histocompatibility complex found on specific white blood cells, including antigen-presenting cells, involved in the adaptive immune response
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4
Q

Explain what a pathogen is

A
  • Pathogens are agents that cause disease to a host
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5
Q

Explain the difference between pathogens and antigens

A
  • Antigens are substances such as pollen, bacteria and viruses that trigger an immune response
  • Pathogens are harmful agents such as bacteria that can cause disease
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6
Q

List the 6 main types of pathogen

A
  • Bacteria, worms, fungi, protozoa, viruses and prions
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7
Q

Compare infection and disease

A
  • Infection is the invasion and growth of a pathogen in the body
  • Disease is a condition that impairs the normal functioning of an organ, structure or system of an organism
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8
Q

Describe the difference between cellular and non-cellular pathogens

A
  • Cellular pathogens are living organisms that are able to reproduce independently
  • Non-cellular pathogens are non-living and require a host to reproduce
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9
Q

Compare extracellular and intracellular pathogens

A
  • Extracellular pathogens are targeted by the humoral immune response
    • Cannot survive inside the phagocyte once ingested
    • In the body but have yet to enter cells
  • Intracellular pathogens are targeted by the cell-mediated immune response
    • Can survive inside of host cells/phagocytes
    • Have entered cells
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10
Q

Explain how viruses damage cells

A
  • Viruses cause disease by killing body cells (cell lysis) and uses the cell’s organelles to reproduce
  • Virus adheres to a host cell, injecting its viral DNA
  • Viral nucleic acid moves to nucleus where it is transcribed
  • Viral mRNA is then translated and viral protein is packaged
  • The infected host cell bursts as its plasma membrane disintegrates and viral particles are released into the extracellular fluid from where they can infect other cells

NOTE: Viruses have either DNA or RNA that is surrounded by a protein shell (capsid).

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11
Q

Explain how bacteria cause disease

A
  • If bacteria multiplies in areas in which they are not normally found, they can cause disease
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12
Q

Define allergen

A
  • Allergens are substances that cause allergic response
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13
Q

Outline the general process of an allergic response

A
  • Allergic response is a reaction to normally harmless antigens
  • Sensitization → initial exposure to allergen
    • Allergen enters the bloodstream, B cells differentiate into plasma cells, plasma cells produce antibodies and antibodies attach to mast cells
    • Mast cells become ‘primed’ with IgE/antibodies specific for the allergen (able to recognise and respond to the allergen)
  • Allergic reaction → secondary exposure to the same allergen
    • Allergen binds to antibodies forming cross links on mast cells, histamine is released from the mast cells and an allergic reaction occurs
    • When an allergen binds to more than one antibody a cross link will form (this results in the release of histamine)
    • No cross link = no histamine produced
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14
Q

Describe the role of mast cells, with clear reference to allergic response

A
  • Mast cells are immune cells that release histamines via degranulation, which causes inflammation
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15
Q

Describe 3 different physical barriers in animals

A
  • Intact skin → the constant shedding of surface cells is an effective barrier against the entry of pathogens
  • Ear wax → reduces the access that pathogens have to the ear drum and ear canal as well as protects the ear from dust and other foreign particles
  • Nasal hair and mucus → trap and prevent the entry of pathogens
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16
Q

Describe 3 different chemical barriers in animals

A
  • Lysozyme → an enzyme present in sweat, tears and saliva that kills pathogens
  • Sebum → an oily secretion produced by sebaceous glands that provides a protective and antimicrobial film on the skin
  • Stomach acid → including digestive enzymes kill pathogens that enter the digestive tract
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17
Q

Explain how microbiological barriers in animals can prevent infection

A
  • Microbiological barriers include harmless bacteria that occur naturally within the body that inhibit the growth of pathogens
  • They do this by secreting antimicrobial chemicals and by outcompeting them for nutrients and adhesion site
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18
Q

Describe 3 different physical barriers in plants

A
  • Waxy cuticle → the waxy coat on leaves that prevent infection
  • Formation of galls → limits the spread of pathogens
  • Thorns → protect plants from grazing animals such as cattle and sheep
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19
Q

Describe chemical barriers in plants

A
  • Caffeine → helps to prevent fungi and insects from invading the plant
  • Antimicrobial enzymes → prevent pathogens from entering the plant
  • Antimicrobial chemicals → produced by plants to disrupt bacterial cell membranes and deter predators
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20
Q

Describe components of the first line of defence that work against viruses

A
  • Mucous membranes make it difficult to viruses to adhere
  • Nose hairs (cilia) are a physical barrier to the virus
  • Acidic environment of the stomach kill viruses
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21
Q

Describe the innate immune response, with specific reference to the second line of defence

A
  • The innate immune response is an inborn system that lacks specifity and memory
  • The second line of defence involves cell-mediated innate immunity, humoral innate immunity, as well as inflammation and fever
  • The second line of defence is in effect once the first line of defence has been breached or when pathogens have entered tissue or the bloodstream
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22
Q

Explain the purpose of a fever

A
  • Increased body temperatures enhance the performance of immune cells, making them work more efficiently
  • Heat can also kill bacteria and viruses as well as denature bacterial enzymes

NOTE: Fevers are part of the second line of defence.

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23
Q

Describe the process of phagocytosis

A
  • A pathogen is identified by a pattern recognition receptor and is engulfed in the plasma membrane of a phagocyte (macrophages, neutrophils or dendritic cells)
  • The pathogen is engulfed in a vesicle called a phagosome
  • Lysosomes fuse with the phagosome
  • Toxic chemicals from the lysosome digest and destroy the pathogen
  • Indigestible material is released through exocytosis
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24
Q

List the main phagocytes in the immune response

A
  • Macrophages, neutrophils and dendritic cells
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25
Q

Compare the roles of macrophages, neutrophils and dendritic cells

A
  • Macrophages eliminate pathogens through phagocytosis
    • They are also antigen presenting cells that activate the adaptive immune response
    • Found in tissues
  • Neutrophils eliminate pathogens through phagocytosis
    • Most abundant and are the first to arrive at an infection site
    • Found in blood
  • Dendritic cells eliminate pathogens through phagocytosis
    • They are also antigen presenting cells that activate the adaptive immune response
    • Found in tissues
    • Occupy and patrol the skin and mucosal surfaces

NOTE: Neutrophils are phagocytes, NOT antigen presenting cells.

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26
Q

Describe the role of eosinophils and how they perform this role

A
  • Eosinophils destroy larger pathogens such as parasites that are too large to be engulfed via phagocytosis
  • They attack via degranulation (releasing cytotoxic chemicals)
  • Found in the respiratory, gastrointestinal and urinary tracts
  • They are also involved in the allergic process
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27
Q

Describe the role of natural killer cells and explain how they destroy virally-infected cells

A
  • Natural killer cells kill virus-infected cells through apoptosis, destroying both the cell and the virus it contains (kills pathogens once they have entered a cell, not the pathogen alone)
  • The NK cell releases perforin and protease enzymes
  • Perforin creates pores in the plasma membrane of the target cell allowing protease to enter
  • Protease enzymes induce apoptosis
  • The infected cell is eliminated
  • Found in blood/lymph
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28
Q

State where mast cells are located and what they contain

A
  • Mast cells are found in tissue beneath the surface of the skin, near vessels and in the respiratory system
  • They contain histamine, cytokines and heparin
29
Q

Describe the role of mast cells

A
  • Mast cells are vital in the inflammatory response
  • They release histamines causing permeability and vasodilation in blood vessels
  • They release cytokines which attracts other immune cells to help destroy the pathogen
30
Q

Define permeability and vasodilation in terms of blood vessels

A
  • Permeability → causes capillaries to be leaky
    • Protein-rich fluid (exudate) can escape from capillaries to the infected region
    • The exudate causes swelling, putting pressure on surrounding tissues and stimulating nerve endings which causes pain
  • Vasodilation → causes capillaries to be wider
    • Increases blood flow to damaged area resulting in heat production and redness
31
Q

Describe complement proteins

A
  • Complement proteins are proteins that assist other innate immune cells to destroy pathogens
  • They are initially inactive but are activated when they make direct contact with antigens
  • Part of the innate (non-specific) immune response

NOTE: Complement proteins are effective on all pathogens, including viruses.

32
Q

Describe how complement proteins can help to remove pathogens

A
  • Lysis → complement proteins interact to form a membrane-attack complex on the plasma membrane of the pathogen
    • The MAC creates a pore in the plasma membrane causing the pathogen to swell and burst
  • Opsonisation → complement proteins coat the surface of pathogens allowing phagocytes to more easily bind to the pathogen
    • Phagocytes have receptors that are complementary to those on the complement proteins (higher likelihood of phagocytosis)
  • Chemotaxis → complement proteins diffuse from the pathogen and attracts immune cells to the site of infection

NOTE: Complement proteins can also coat bacteria to prevent binary fission (replication).

33
Q

State what interferons are

A
  • Interferons are a subgroup of cytokines (signalling proteins) that are made and released by virally infected cells or host cells
  • They interfere with viral replication
  • Part of the innate immune response
34
Q

State 4 effects that interferons can have

A
  • Activate immune cells such as NK cells
  • Signals neighbouring infected cells to undergo apoptosis
  • Signals neighbouring uninfected cells to reduce protein synthesis
  • Signals change in plasma membrane to prevent further entry of the virus
35
Q

Describe the 3 stages of inflammation (VCR), including the role of various cells and proteins

A
  • Vascular stage involving blood cells
    • Mast cells release histamines causing permeability and vasodilation in cappilaries (blood vessels)
  • Cellular stage involving immune cells
    • Cytokines released by mast cells attract phagocytes such as macrophages and dendritic cells
    • Complement proteins opsonise the pathogen allowing phagocytosis to occur
    • Platelets travel to the site to block the wound (clotting)
    • Pus (consisting of dead tissue and pathogens) indicates that this stage is occuring
  • Resolution stage when the antigen is removed
    • Occurs when tissue is returned to its normal state and the infection is under control
    • If the resolution stage is not reached, chronic inflammation may occur
36
Q

Outline the process that leads to a sore and inflamed throat

A
  • Upon cell destruction in the throat, chemicals are released that cause increased membrane permeability and swelling
  • Vasodilation allows more immune cells to move to the site
  • Mast cells release histamines, which causes inflammation
37
Q

Outline how antigen presenting cells present antigens

A
  • An antigen is enfgulfed by a dendritic cell or macrophage (antigen presenting cells)
  • The antigen is destroyed and fragments are presented on MHC-II molecules
  • The APC presents the antigen to specific helper T cells
38
Q

State where antigen presentation occurs

A
  • Lymph nodes
39
Q

Explain the role of T helper cells

A
  • They are activated by antigen-presenting cells that present antigens on their MHC II markers
  • Once active, they clone and secrete cytokines (interleukins) which activates either the humoral adaptive immune response (B cells) or the cell-mediated adaptive immune response (cytotoxic T cells)
40
Q

Explain the role of cytotoxic T cells

A
  • Upon the release of cytokines from helper T cells, cytotoxic T cells proliferate (multiply), producing activated cytotoxic T cells and memory T cells via clonal selection and expansion
  • Cytotoxic T cells destroy the target cell through apoptosis
41
Q

Outline the function of the lymphatic system

A
  • The lympathic system acts as a transport network
  • Allows for antigen recognition
  • Involved in the production and maturation of immune cells
  • The removal of excess fluids from body tissues
  • Absorption and transportation of fatty acids to the digestive system
42
Q

List and state the function of the primary lymphoid organs

A
  • Primary lymphoid organs are where immune cells are produced and mature
  • Bone marrow is the site in which all immune cells originate (including red blood cells and T cells) and where B cells mature
  • The thymus is where T cells mature after being released from the bone marrow
43
Q

List and state the function of the secondary lymphoid organs

A
  • Secondary lymphoid organs are where immune cells are activated by meeting antigens and where immune responses occur
  • The spleen filters blood clearing it from bacteria, viruses or worn-out red blood cells
  • Lymph nodes are the site for antigen recognition
44
Q

Describe both the structure and function of lymph nodes

A
  • Lymph nodes are small bean shaped structures located in the armpits, neck, groin and abdomen
  • Composed of lymphoid tissue with clusters of lymphocytes residing within the lymphatic system
  • They are sites where antigen presentation occurs and activates T and B cells
  • Swelling due to infection occurs because the number of B and T cells in the lymph nodes increase
  • Valves in lymph nodes prevent the backward flow of lymph fluid
45
Q

Describe how the lympathic system acts as a transport network for immune cells

A
  • Immune cells can travel around the body through the lymph
46
Q

Describe the key features of the adaptive immune response

A
  • T and B cells (special white blood cells known as lymphocytes)
  • Antibodies, also known as immunoglobulins (special antigen-binding proteins)
  • Secondary lymphoid organs where B and T cells meet foreign antigens and are activated, and where adaptive immune responses occur
47
Q

Define clonal expansion and clonal selection

A
  • Clonal expansion is when activated cells divide into many identical copies (clones)
  • Clonal selection is when a cell binds with its specific antigen
48
Q

Explain adaptive immunity

A
  • Adaptive immunity involves a specific response against a specific pathogen where memory is retained for future infection
  • Usually only required if an infection is not cleared by the innate response
  • Specificity refers to adaptive immune cells (B and T cells) having unique receptors that recognise specific antigens
  • Immunological memory refers to the ability for the immune system to remember antigens from previous infections which enables a stronger and more rapid immune response upon reinfection with the same antigen
49
Q

Outline the humoral and cell-mediated parts of the adaptive immune response

A
  • Humoral immunity is a response that occurs in body fluids
    • It involves the actions of B lymphocytes and their antibodies
  • Cell mediated immunity is a response that kills body cells
    • Involves the actions of cytotoxic T cells
  • Both produce memory
50
Q

Outline how the cell-mediated response removes body cells infected by viruses (or cancerous)

A
  • Upon antigen recognition, helper T cells clone and secrete cytokines
  • Cytotoxic T cells proliferate producing activated cytotoxic T cells and memory T cells through clonal selection and expansion
  • Cytotoxic T cells destroy the cells through apoptosis
51
Q

Outline how cytotoxic T cells attack antigens

A
  • Cytotoxic T cells release perforin that enters a target cell and create pores in its plasma membrane
  • Cytotoxic T cells also release protease enzymes that enter the infected cell via the pore and initiate apoptosis
  • The cytotoxic T cells are then free to attack other infected cells that display the same foreign antigen

NOTE: Apoptosis by cytotoxic T cells, unlike NK cells, are specific for certain antigens and form memory.

52
Q

Describe the key components and functions of the humoral adaptive response

A
  • B cells are activated by binding to pathogens or cytokines secreted by T helper cells
    • Some become memory cells (stored in lymphatic system)
    • Some become plasma cells (floats around the bloodstream)
  • Plasma cells make antibodies
    • Antibodies work against the pathogen (PIANO)
53
Q

Outline how the humoral immune response removes extracellular pathogens from the body fluids

A
  • B lymphocytes (cells) are covered in specific receptors and are activated by T helper cells
  • When activated by a T helper cell, B cells replicate (clonal expansion) producing plasma cells and memory cells
  • The plasma cells make antibodies which can opsonise or agglutinate pathogens
54
Q

Describe the difference between memory cells and plasma cells

A
  • Memory cells
    • Inactive
    • Lifelong
    • Produce rapid and enhanced immune responses upon secondary exposure to a previously identified antigen
  • Plasma cells
    • Active
    • Tend to live shorter than memory cells
    • Gives protection by producing antibodies
    • Each type of plasma produces one specific type of antibody
55
Q

Outline the process that leads to the production of antibodies

A
  • When a pathogen comes into contact with a B cell, the B cell divides and clones to produce memory and plasma cells
  • Plasma cells produce antibodies that act against the pathogen
56
Q

Draw and label the structure of an antibody

A
  • Diagram should include
    • 2 heavy and 2 light polypeptide chains
    • Variable and constant region
    • 2 identical specific antigen-binding sites

NOTE: Antibodies have a quaternary structure. They are composed of 4 polypeptide chains that are held together by disulphide bonds.

57
Q

Explain what creates the difference in variable regions for an antibody

A
  • Antigenic variation
  • The shuffling of nucleotides that code for variable regions create different combinations
  • These combinations code for varying protein structures
58
Q

Describe the effects of antibodies (PIANO)

A
  • Precipitation → antibodies bind to soluble agents making them insoluble to create a solid that is more visible to the immune system (due to cross-linking between antigens and antibodies)
  • Inflammation → antibodies initiate the release of histamine by binding to mast cells
  • Agglutination → antibodies bind to antigens forming antigen-antibody complexes causing them to clump together and become more visible to the immune system
  • Neutralisation → antibodies bind to antigens and block their receptors so that the pathogens cannot attach to healthy body cells and infect them
  • Opsinisation → antibodies bind to antigens to make them more susceptible to phagocytosis

NOTE: Antibodies do not directly eliminate pathogens.

59
Q

Describe 3 ways that antibodies can neutralise pathogens

A
  • Bind to antigens to stop them from functioning
  • Coat the surface of antigens to make them more susceptible to phagocytosis (opsinisation)
  • Bind to antigens to initiate lysis by complement proteins
60
Q

Describe the difference between natural and artificial immunity

A
  • Natural immunity is a form of immunity that occurs naturally without deliberate intervention
  • Artificial immunity is a form of immunity that is created via deliberate intervention or exposure to an antigen
61
Q

Describe the differences between active and passive immunity

A
  • Active immunity involves antibodies being produced by an individual’s own immune system in response to exposure to a particular antigen
    • Secondary response is enhanced due to memory, long lasting, more effective, immunity is developed over weeks
  • Passive immunity involves antibodies being acquired from an external source
    • No immunological memory, short lasting, less effective, immunity is immediate
62
Q

State ways in which natural immunity can develop

A
  • Antibodies naturally produced in response to catching a cold
  • Mother-child (breastfeeding)
  • Contracting chicken pox via “chickenpox parties”
63
Q

State 2 ways in which artificial immunity can develop

A
  • Vaccination (deliberate exposure to a pathogen to produce antibodies)
  • Injection of antibodies
64
Q

State 2 ways in which active immunity can develop

A
  • Vaccines
  • Infection
65
Q

State 2 ways in which passive immunity can develop

A
  • Mother-child
  • Injection of antibodies

NOTE: No memory cells are produced due to a lack of exposure to the antigen.

66
Q

State the function of ducts leading to and leading from the lymph nodes

A
  • Ducts leading to the lymph nodes
    • Carry APCs that display antigens on the MHC-II molecules
    • Carry free-floating antigens
  • Leading from the lymph nodes
    • Carry specific cytotoxic T cells
    • Carry specific helper T cells
    • Carry specific antibodies

NOTE: From NEAP 2023 exam.

67
Q

List the changes that occur during an inflammatory response

A
  • Increased…
  • Mast cell activation
  • Histamine release
  • Blood flow to the area
  • Swelling
  • Blood vessel dilation
  • Clotting factors
68
Q

Distinguish between T memory and B memory cells

A
  • T memory cells proliferate into T helper cells and cytotoxic T cells when the body is exposed to a previously identified pathogen, mounting a quicker and stronger immune response
  • B memory cells will rapidly divide and form new antibody-producing plasma cells

NOTE: T memory cells are involved in cell-mediated immunity while B memory cells are involved in humoral immunity.

Biology U3/4 (12 decks)

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