3.2.4 Cell recognition and the immune system

Question 1

What specific molecules on cell surfaces enable identification by the immune system?

Answer 1

Proteins with specific tertiary structures that act as antigens.

Question 2

What are the four things the immune system can identify using specific molecules on cell surfaces?

Answer 2

Pathogens, non-self cells (e.g. cells from other organisms of the same species), abnormal body cells (e.g. cancer cells), toxins.

Question 3

What is the role of proteins on the surface of cells?

Answer 3

To act as antigens with specific tertiary structures which are recognized by the immune system.

Question 4

Give an example of an abnormal body cell that the immune system can identify.

Answer 4

Cancer cells displaying abnormal antigens.

Question 5

What term describes cells from other organisms of the same species that can be identified by the immune system?

Answer 5

Allogeneic cells identified as non-self.

Question 6

What feature of toxins allows the immune system to identify them?

Answer 6

The specific shape of their antigenic determinants.

Question 7

How does the immune system differentiate between self and non-self cells?

Answer 7

By recognizing antigens; self-cells display self-antigens while non-self cells display foreign antigens.

Question 8

What is the definition of an antigen?

Answer 8

An antigen is a molecule, often a protein, with a specific tertiary structure that triggers a specific immune response by being recognized as non-self by the immune system.

Question 9

How does antigen variability affect disease?

Answer 9

Antigen variability caused by genetic mutations or recombination changes the specific proteins on a pathogen’s surface. This helps pathogens evade immune recognition, leading to persistent or recurrent infections. For example, the influenza virus frequently alters its antigens, requiring updated vaccines.

Question 10

How does antigen variability impact disease prevention?

Answer 10

Antigen variability reduces vaccine effectiveness because changes in surface antigens mean the immune system may not recognize the pathogen. Vaccines such as the flu vaccine must be updated regularly to match these new antigenic forms and maintain protection.

Question 11

What is phagocytosis?

Answer 11

The process by which phagocytes engulf and ingest pathogens.

Question 12

What happens to pathogens after phagocytosis?

Answer 12

Ingested pathogens are destroyed by lysozymes within the phagocyte.

Question 13

What is the cellular response in the immune system?

Answer 13

The activation of T lymphocytes in response to a foreign antigen.

Question 14

How do T lymphocytes respond to a foreign antigen?

Answer 14

T lymphocytes bind to antigens presented on the surface of antigen-presenting cells, leading to their activation and clonal expansion.

Question 15

What is the role of antigen-presenting cells in the cellular response?

Answer 15

Antigen-presenting cells display antigens on their surface to activate T lymphocytes.

Question 16

What is the role of helper T cells (TH cells) in the immune response?

Answer 16

Helper T cells stimulate cytotoxic T cells (TC cells) to kill infected cells, activate B cells to produce antibodies, and enhance the activity of phagocytes by releasing cytokines which amplify phagocytic activity.

Question 17

What is the humoral response?

Answer 17

The activation of B lymphocytes in response to a foreign antigen, leading to the production of monoclonal antibodies.

Question 18

What is clonal selection in the humoral response?

Answer 18

The process by which specific B lymphocytes with complementary receptors to the foreign antigen are activated and cloned.

Question 19

What do B lymphocytes release after activation?

Answer 19

B lymphocytes release monoclonal antibodies specific to the foreign antigen.

Question 20

What is the definition of an antibody?

Answer 20

An antibody is a protein produced by B lymphocytes that binds specifically to a complementary antigen, triggering its destruction.

Question 21

What is the structure of an antibody?

Answer 21

Antibodies consist of four polypeptide chains (two heavy chains and two light chains) held together by disulfide bonds. They have a variable region that binds to a specific antigen and a constant region.

Question 22

What happens when an antigen-antibody complex forms?

Answer 22

The formation of an antigen-antibody complex leads to the destruction of the antigen through agglutination and phagocytosis of bacterial cells.

Question 23

What is the role of plasma cells in the immune response?

Answer 23

Plasma cells are activated B lymphocytes that produce and release large quantities of monoclonal antibodies during the primary immune response.

Question 24

What is the role of memory cells in the immune response?

Answer 24

Memory cells are long-lived B lymphocytes that remain in the body after the primary immune response, enabling a faster and stronger secondary immune response upon re-exposure to the same antigen.

Question 25

How do vaccines provide protection against disease?

Answer 25

Vaccines contain antigens from a pathogen, stimulating the production of memory cells without causing disease, leading to immunity.

Question 26

What is herd immunity?

Answer 26

Herd immunity occurs when a significant portion of a population is vaccinated, reducing the spread of the disease and protecting individuals who are not immune.

Question 27

What is active immunity?

Answer 27

Active immunity involves the production of antibodies by the immune system after exposure to an antigen, either through infection or vaccination.

Question 28

What is passive immunity?

Answer 28

Passive immunity involves the transfer of antibodies from another source, such as maternal antibodies through the placenta or injection of antiserum, providing temporary immunity.

Question 29

What are the differences between active and passive immunity?

Answer 29

Active immunity is long-lasting, involves memory cell formation, and takes time to develop, while passive immunity is immediate, short-term, and does not involve memory cells.

Question 30

What is the structure of HIV?

Answer 30

HIV consists of an RNA genome enclosed in a capsid, surrounded by a lipid envelope embedded with glycoproteins.

Question 31

How does HIV replicate in helper T cells?

Answer 31

HIV binds to the CD4 receptors on helper T cells using its glycoproteins, fuses with the cell membrane, and releases its RNA. Reverse transcriptase converts the RNA into DNA, which integrates into the host's genome. The host cell machinery produces new viral particles.

Question 32

How does HIV cause the symptoms of AIDS?

Answer 32

HIV destroys helper T cells, reducing their numbers and impairing the immune response. This makes the body susceptible to opportunistic infections and cancers.

Question 33

Why are antibiotics ineffective against viruses?

Answer 33

Antibiotics target bacterial structures and metabolic pathways, such as cell walls and ribosomes, which are absent in viruses. Consequently, antibiotics cannot disrupt viral replication.

Question 34

How are monoclonal antibodies used in targeting medication?

Answer 34

Monoclonal antibodies are attached to therapeutic drugs. These antibodies bind specifically to antigens on target cell types, delivering the drug directly to the diseased cells and minimizing side effects.

Question 35

How are monoclonal antibodies used in medical diagnosis?

Answer 35

Monoclonal antibodies are used to detect specific antigens or proteins in diagnostic tests, such as detecting biomarkers for diseases like cancer or infections.

Question 36

What are some ethical issues associated with the use of vaccines?

Answer 36

Ethical issues include concerns about testing vaccines on animals or humans, the cost and accessibility of vaccines, and the potential side effects.

Question 37

What are some ethical issues associated with the use of monoclonal antibodies?

Answer 37

Ethical issues include the use of animals in their production, the cost of treatment, and the potential for side effects.

Question 38

What is the purpose of the ELISA test?

Answer 38

The ELISA test detects the presence and quantity of specific antigens or antibodies in a sample, such as diagnosing infections like HIV. Detecting antigens allows for early diagnosis of disease, while detecting antibodies indicates an immune response to a pathogen.

Question 39

How does the ELISA test work?

Answer 39

The test involves attaching an antigen or antibody to a surface, adding the sample, and using enzyme-linked antibodies that produce a color change to indicate a positive result.

Question 40

Describe the role of the disulfide bridge bonds in an antibody

Answer 40

joins two (different) polypeptides

Question 41

Explain why antibodies will only bind with specific antigens.

Answer 41

antibodies have a variable region that has a specific amino acid sequence OR primary structure the shape OR tertiary structure of the binding site is complementary to specific antigens forms a complex between the antigen and antibody OR forms an antigen-antibody complex

Question 42

Describe how phagocytes destroy pathogens.

Answer 42

engulfs/endocytosis forms a vesicle/phagosome AND fuses with a lysosome enzymes/lysozymes digest/hydrolyse the pathogen

Question 43

What is an antigen?

Answer 43

a molecule/protein/glycoprotein that stimulates an immune response

Question 44

Other than pathogens, give two types of cell that may stimulate an immune response.

Answer 44

cells from other organisms OR cells from transplants abnormal/cancer/tumour cells cells infected by a virus own/host cells in an autoimmune disease

Question 45

Explain how the release of antibodies stimulates the process of phagocytosis.

Answer 45

antibodies bind to antigens OR antibodies are markers/opsonins OR antibodies form antigen-antibody complexes antibodies cause clumping/agglutination OR antibodies attract phagocytes

Question 46

Explain why a high mutation rate makes it difficult to develop a vaccine.

Answer 46

high mutation rate leads to the antigens changing OR high mutation rate leads to antigenic variability vaccines (often) contain a specific antigen antibodies will not be complementary to a changed antigen OR antibodies will not bind to changed antigens

Question 47

Explain how HIV affects the production of antibodies when AIDS develops.

Answer 47

less/no antibodies produced because HIV destroys helper T cells so few/no B cells are activated OR few/no B cells undergo mitosis OR few/no B cells differentiate into plasma cells

Question 48

Explain how the destruction of T cells by HIV eventually leads to death of the affected individual.

Answer 48

nsufficient/no T cells to activate B cells OR insufficient/no T cells to activate the immune system individual unable to fight off infections/cancer/diseases OR individual more prone to infections/cancer/diseases example of infection/cancer/disease (e.g. TB/tuberculosis or pneumonia)

Question 49

What is an antibody?

Answer 49

a protein/immunoglobulin specific to an antigen produced by B cells OR secreted by plasma cells

Question 50

Explain how vaccines can be used to protect people against disease.

Answer 50

vaccines contain antigens OR vaccines contain dead/weakened pathogens memory cells are made on second exposure to the antigen/pathogen, memory cells (divide into plasma cells that) produce antibodies memory cells rapidly (divide into plasma cells that) produce antibodies OR memory cells (divide into plasma cells that) produce more antibodies antibodies destroy pathogens

Question 51

Explain the differences between active and passive immunity.

Answer 51

active immunity involves memory cells, passive immunity does not active immunity involves the production of antibodies by plasma cells passive immunity involves antibodies being introduced into the body from outside active immunity is long term because antibodies are produced in response to antigens passive immunity is short term because the antibodies given are broken down active immunity can take time to develop, passive immunity is fast acting

Question 52

Describe how HIV is replicated. (4)

Answer 52

1. Attachment proteins attach to receptors on helper T cell/lymphocyte; 2. Nucleic acid/RNA enters cell; 3. Reverse transcriptase converts RNA to DNA; 4. Viral protein/capsid/enzymes produced; 5. Virus (particles) assembled and released (from cell);

Question 53

Describe how a phagocyte destroys a pathogen present in the blood. (3)

Answer 53

1. Engulfs; Accept endocytosis OR Description Ignore ‘taken in’ 2. Forming vesicle/phagosome and fuses with lysosome; 3. Enzymes digest/hydrolyse; Accept lysozymes for ‘enzymes’

Question 54

Give two types of cell, other than pathogens, that can stimulate an immune response. (2)

Answer 54

1. (Cells from) other organisms/transplants; 2. Abnormal/cancer/tumour (cells); 3. (Cells) infected by virus; Accept ‘own cells’ if autoimmune response suggested Accept APCs Accept non-self

Question 55

What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

Answer 55

Joins two (different) polypeptides;

Question 56

Explain how HIV affects the production of antibodies when AIDS develops in a person. (3)

Answer 56

1. Less/no antibody produced; 2. (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’ 3. (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;

Question 57

Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how. (2)

Answer 57

1. (The scientists) could identify proteins (that derive from the genetic code) OR (The scientists) could identify the proteome; 2. (They) could (then) identify potential antigens (to use in the vaccine); Reject if answer suggests vaccine contains antibodies

Question 58

What is a monoclonal antibody? (1)

Answer 58

(Antibodies with the) same tertiary structure OR (Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes;

Question 59

Give one example of using monoclonal antibodies in a medical treatment. (1)

Answer 59

Targets/binds/carries drug/medicine to specific cells/antigens/receptors OR Block antigens/receptors on cells;

Question 60

Describe the role of antibodies in producing a positive result in an ELISA test. (4)

Answer 60

1. (First) antibody binds/attaches /complementary (in shape) to antigen; 2. (Second) antibody with enzyme attached is added; 3. (Second) antibody attaches to antigen; Accept (second) antibody attaches to (first) antibody (indirect ELISA test). 4. (Substrate/solution added) and colour changes; Only award if enzyme mentioned.

Question 61

Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis. (2)

Answer 61

1. Bind to antigen OR Are markers; Accept opsonin for ‘marker’ Accept form (antibody-antigen) complexes/are complementary to antigen 2. (Antibodies) cause clumping/agglutination OR Attract phagocytes; Reject clotting

Question 62

Describe how phagocytosis of a virus leads to presentation of its antigens. (3)

Answer 62

1. Phagosome / vesicle fuses with lysosome; 2. (Virus) destroyed by lysozymes / hydrolytic enzymes; 3. Peptides / antigen (from virus) are displayed on the cell membrane;

Question 63

Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen. (3)

Answer 63

1. Helper T cell / TH cell binds to the antigen (on the antigen- presenting cell / phagocyte); 2. This helper T / TH cell stimulates a specific B cell; 3. B cell clones OR B cell divides by mitosis; 4. (Forms) plasma cells that release antibodies;

Question 64

What is an antigen? (2)

Answer 64

1. Foreign protein; Accept glycoprotein / glycolipid / polysaccharide 2. (that) stimulates an immune response / production of antibody;

Question 65

What is an antibody? (2)

Answer 65

1. A protein / immunoglobulin specific to an antigen; 2. Produced by B cells OR Secreted by plasma cells;

Question 66

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. (5)

Answer 66

1. Vaccine contains antigen from pathogen; 2. Macrophage presents antigen on its surface; 3. T cell with complementary receptor protein binds to antigen; 4. T cell stimulates B cell; 5. (With) complementary antibody on its surface; 6. B cell secretes large amounts of antibody; 7. B cell divides to form clone all secreting / producing same antibody.

Question 67

Describe the difference between active and passive immunity.

Answer 67

1. Active involves memory cells, passive does not; 2. Active involves production of antibody by plasma cells / memory cells; 3. Passive involves antibody introduced into body from outside / named source; 4. Active long term, because antibody produced in response to antigen; 5. Passive short term, because antibody (given) is broken down; 6. Active (can) take time to develop / work, passive fast acting.

Question 68

Describe how phagocytosis of a virus leads to presentation of its antigens

Answer 68

1. Phagosome/vesicle fuses with lysosome; 2. (Virus) destroyed by lysozymes/hydrolytic enzymes; 3. Peptides/antigen (from virus) are displayed on the cell membrane;

Question 69

Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.

Answer 69

1. Helper T cell/TH cell binds to the antigen (on the antigen-presenting cell/phagocyte); 2. This helper T/TH cell stimulates a specific B cell; 3. B cell clones OR B cell divides by mitosis; 4. (Forms) plasma cells that release antibodies;