immunology

Question 1

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

Answer 1

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

Question 2

Describe how a phagocyte destroys a pathogen present in the blood.

Answer 2

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

Question 3

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

Answer 3

. (Cells from) other organisms/transplants;
. Abnormal/cancer/tumour (cells);
. (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

Answer 4

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

Question 5

Explain how the humoral response leads to immunity.

Answer 5

. B cells specific to the antigen reproduce by mitosis.
. B cells produce plasma and memory cells
. 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.

Answer 7

. Active involves memory cells, passive does not;
. Active involves production of antibody by plasma cells/memory cells;
. Passive involves antibody introduced into body from outside/named source;
. Active long term, because antibody produced in response to antigen;
. Passive short term, because antibody (given) is broken down;
. 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.

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).

Answer 10

. RNA (as genetic material);
. Reverse transcriptase (makes copy of DNA from RNA);
. (Protein) capsomeres/capsid (surrounds genetic material of virus);
. (Phospho)lipid (viral) envelope OR Envelope made of membrane;
. Attachment proteins (used to attach to host t cell);

Question 11

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

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;
. (More 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.

Answer 12

. (First) antibody binds/attaches /complementary (in shape) to antigen;
. Wash unbound antigen;
. (Second) antibody with enzyme attached is added;
. (Second) antibody attaches to antigen;
. Wash unbound antibodies with enzymes;
. (Substrate/solution added) and colour changes = positive result