Immunology

Question 1

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

Answer 1

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

Question 2

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

Answer 2

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

Question 3

State TWO ways in which pathogens cause harm / disease

Answer 3

• Secrete TOXINS (proteins)
• Damage /Destroy cells/tissues/organs

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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 6

Explain how the humoral response leads to immunity.

Answer 6

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 7

Describe and explain the role of antibodies in stimulating phagocytosis.

Answer 7

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

Question 8

Describe the difference between active and passive immunity.

Answer 8

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 9

State why some antibodies are referred to as monoclonal

Answer 9

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

OR

(Antibodies) produced from the same B cell / plasma cell;

Question 10

State 2 methods of delivering passive immunity

Answer 10

1. Antibodies from mother pass across the placenta to bind to specifically complementary antigens on pathogens that have also crossed the placenta
2. Through breast milk
3. Through plasma transfusion
4. Through ANTI-VENOM / ANTI-TOXIN injections

Question 11

Explain how a fetus is protected against a pathogen that infects its mother during pregnancy.

Answer 11

• Antibodies have variable regions with specific tertiary structures
• Complementary to antigens
• Found on pathogen which has crossed the placenta
• forms antigen-antibody complexes