IMMUNITY

Question 1

what is an antigen (2)

Answer 1

Protein on surface/membrane (of cell);
causes an immune response ;

Question 2

describe the difference between active and passive immunity (5)

Answer 2

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;
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 3

when a pathogen enters the body it may be destroyed by phagocytosis. explain how (4)

Answer 3

1.Phagocyte recognises foreign antigen;
2.Pathogen engulfed / ingested;
3.Enclosed in vacuole, forming a phagosome;
4.Vacuole fuses with lysosome;
5.Lysosome contains enzymes that are emptied into the vacuole;
6. Pathogen digested / molecules hydrolysed;

Question 4

describe how B-lymphocytes respond when they are stimulated by antigens (4)

Answer 4

Divide by mitosis to form clones;
Produce plasma cells;
Plasma cells make antibodies;
Plasma cells produce memory cells

Question 5

an antigen in a vaccine leads to the production of antibodies. describe the part played by B lymphocytes in this process (4)

Answer 5

1 Macrophages present antigens to B lymphocytes;
2 antigen binds to complementary receptors on B lymphocyte;
3 lymphocyte becomes activated;
4 (B) lymphocytes reproduce by mitosis;
5 plasma cells secrete antibodies;

Question 6

what is a monoclonal antibody (2)

Answer 6

Antibodies from the same plasma cell;
Specific to/complementary to only one antigen;

Question 7

what is vaccination (2)

Answer 7

Injection of antigens from attenuated microorganism;
Stimulates the formation of memory cells;

Question 8

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

Answer 8

1.Vaccine contains antigen from pathogen;
2.Antigen is displayed on antigen-presenting cells (macrophages);
3.Helper T cell with complementary receptor protein binds to antigen;
4.Helper T cell stimulates B cell;
5.With the complementary antibody on its surface;
6.B cell secretes large amounts of antibody;
7.B cell divides to form clone which produces the same antibody

Question 9

vaccines protect people against disease. explain how ( 5)

Answer 9

1.Vaccines contain antigens from a dead/weakened pathogens are injected;
2.Memory cells made;
3.On second exposure memory cells produce become active and produce antibodies;
4.Rapidly produce antibodies/ produces more antibodies;
5.Antibodies destroy pathogens;

Question 10

scientists use an antibody to detect an antigen on the bacterium that causes stomach ulcers. explain why the antibody will only detect this antigen (3)

Answer 10

1. Antibody has a variable region with a specific amino acid sequence / primary structure;
2. The shape of tertiary structure of the binding site;
3. Complementary to the antigens;
4. Forms complex between antigen and antibody;

Question 11

describe how HIV is replicated after it has entered a human cell (4)

Answer 11

Reverse transcriptase;
Enzyme uses HIV RNA to make DNA copy;
DNA joined to host cell’s DNA/chromosome;
DNA used to make HIV RNA copies;
And HIV capsid proteins/enzymes;
Made at host ribosomes;
Assembly of new virus particles;
Budding off from membrane of host cell;

Question 12

describe how HIV is replicated once inside of Th cells (4)

Answer 12

1.RNA converted into DNA using reverse transcriptase;
2.DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
3.DNA transcribed into (HIV m)RNA;
4.(HIV mRNA) translated into (new) HIV/viral proteins (for assembly into
viral particles);