Immunology

Question 1

Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)

Answer 1

The process is called phagocytosis – No Mark
1. Pathogen is engulfed by the phagocyte.
2. Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle;
3. Lysosomes fuse with vesicle releasing
digestive enzymes;
4. Lysosome enzymes break down the pathogen.
5. Waste materials are ejected from the cell by exocytosis;

Question 2

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

Answer 2

1. Engulfs;
2. Forming vesicle/phagosome and fuses with lysosome;
3. Enzymes digest/hydrolyse;

Question 3

Give two types of cell, other than pathogens, that can stimulate an immune response (3)

Answer 3

1. (Cells from) other organisms/transplants;
2. Abnormal/cancer/tumour (cells);
3. (Cells) infected by virus;

Question 4

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how (7)

Answer 4

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

Question 5

Explain how the humoral response leads to immunity (3)

Answer 5

1. B cells specific to the antigen reproduce by mitosis.
2. B cells produce plasma and memory cells
3. Second infection produces antibodies in larger quantities AND quicker.

Question 6

Describe and explain the role of antibodies in stimulating phagocytosis.

Answer 6

• • Bind to antigen OR Are markers;
• Antibodies cause clumping/agglutination OR Attract phagocytes;

Question 7

Describe the difference between active and passive immunity (6)

Answer 7

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 8

State why some antibodies are referred to as monoclonal

Answer 8

Antibodies produced from a single clone of B cells / plasma cells;
OR

Antibodies produced from the same B cell / plasma cell;

Question 9

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why (3)

Answer 9

• Specific) primary structure / order of amino acids;
• (Specific) tertiary / 3D structure / shape;
• (So) Only binds to / fits / complementary to one antigen;

Question 10

Describe the structure of the human immunodeficiency virus (HIV) (5)

Answer 10

1. RNA (as genetic material);
2. Reverse transcriptase;
3. (Protein) capsomeres/capsid;
4. (Phospho)lipid (viral) envelope OR Envelope made of membrane;
5. Attachment proteins;

Question 11

Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections (4)

Answer 11

• High viral load leads to increased destruction of helper T/CD4 cells;
• Less activation of B cells/cytotoxic T cells/phagocytes;
• Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
• (less able to) destroy other microbes/pathogens OR (More able to) destroy mutated/cancer cells;

Question 12

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

Answer 12

1. (First) antibody binds/attaches /complementary (in shape) to antigen;
2. 2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen;
4. (Substrate/solution added) and colour changes;

Question 13

Antigen definition

Answer 13

Molecule that stimulates a immune response resulting in production of specific antibodies

Question 14

Specific Immunity definition

Answer 14

Specific response to Specific antigen on surface of cell

Question 15

Clonal selection (3)

Why is this method required?

Answer 15

• Specific TH cell binds to presented antigen via complementary receptor
• TH cell activated = clones produce many TH cells with complemntary recpector antigen

Not enough room in body to have lots of every T cell.

Increased num of cells = increased totaly energy demanded

Question 16

Role of TH Helper cell (5)

Answer 16

1. Specific TH cell binds to antigen presenting cell
2. Releases cytokines = attracts phagocyte to infected area
3. Releases cytokines = activates Tc cells
4. Activates specific complementary B cells
5. Forms memory TH cells

Question 17

Role of Tc cells (4)

Answer 17

1. Locates + destroys infected body cells that present correct antigen
2. Binds to antigen presenting cell
3. Releases protein = creates hole in cell surface membrace = destroys APC

Question 18

Humoral response definition (3)

Where do B cells come from

Answer 18

Involves activation of B cells to produce antibodies
B cells must be stimulated by complementary TH cells by release of cytokines

Question 19

Antibody definition

How is a specific antibody formed

Answer 19

Quaternary protein made in response to foreign antigen = specific binding site

From a specific plasma cell

Question 20

How do antibodies assist in destruction of pathogens

Aggulation, Opsonisation, Lysis, Anti toxin

Answer 20

*Aggulation - Specific antibodies bind to antigen + clump them together
* Oponisation. - Marking phathogen so phagocyte can recognise + destroy them efficently
* Lysis - bind to antigen = causes destruction of pathogen membrane
* Anti toxin - Bind to toxin to prevent molecules from binding to target
* Preventing pathogen replication

Question 21

Secondary response definition

Answer 21

Activation of memory cells from antibodies

Question 22

HIV replication - using TH cells (7)

Answer 22

1. Protein on HIV binds to protein found on TH cell
2. Capsid fuses with cell surface membrane + releases viral mRNA and enzymes into TH cells
3. HIV reverse trascripase converts viral mRNA to cDNA using host nucleotides
4. cDNA moves into nucleus of T cells and is inserted into host genome = person infected
5. T cells manufacture HIV particles
6. Particles break away from TH cell forming lipid envelope with TH recpetor proteins
7. Reduction in number of TH cells due to inactivation of TH cells

Question 23

How antibiotics work (2)

Answer 23

1. Antibiotics prevent bactieral making murein cell wall
2. Bacteria unable to resist osmotic presure = burst open due to increased vol in cell

Question 24

Explain why Antibiotics can’t be used for Viruses

Answer 24

1. Viruses dont have any organelles to disrupt (use host cell organellese to carry out metabolic activites)
2. Viruses have Capsid = doesnt allow antibiotic to damage virus