The Immune System

Question 1

Phagocytosis

Answer 1

Phagocyte recognises foreign antigens on pathogen
Phagocyte cytoplasm surrounds and engulfs pathogen
Pathogen contained in phagocytic vacuole in phagocyte cytoplasm
Lysosome fuses with vacuole
Lysozymes break down pathogen
Phagocyte presents pathogen’s antigens on its surface
other immune system cells activated

Question 2

Phagocyte

Answer 2

i.e. a macrophage
form of WBC
carries out phagocytosis
first to respond to pathogens
found in blood and tissues

Question 3

T-Cells

Answer 3

Activated by Phagocytes
different form of WBC
its receptor proteins bind to complementary antigens presented by phagocytes
T cell is then activated

Question 4

Helper T Cells

Answer 4

release chemical signals to activate and stimulate phagocytes and cytotoxic T cells
Activate B cells

Question 5

Cytotoxic T cells

Answer 5

kill abnormal and foreign cells.

Question 6

B Cells

Answer 6

Activated by T cells
WBC
covered in antibodies
bind to antigens forming antigen-antibody complexes
Each B cell has unique antibody on membrane
Clonal selection: Substances released from T Cell and binding activates B Cell
Activated B cell divides into plasma cells

Question 7

Plasma Cells

Answer 7

Identical to B cells
secrete many antibodies complementary to the antigen (monoclonal antibodies/MABS)
form many antigen-antibody complexes

Question 8

Antibodies

Answer 8

Two binding sites - can bind to two pathogens at the same time
TF pathogens become clumped together - AGGLUTINATION
Phagocytes bind to antibodies and phagocytose many pathogens at once
process leads to destruction of pathogens carrying antigen in body

Question 9

Antibody Structure

Answer 9

PROTEINS
specificity relies on variable regions
variable regions form antigen binding sites
each type of antibody has unique variable region (why only one antibody per pathogen)
All antibodies have the same constant regions
disulfide bridges keep constant regions together
hinge protein gives antibody ‘Y’ shape
| = heavy chain
\/ = light chains

Question 10

Cellular Response

Answer 10

T cells and other immune system cells that they interact with
i.e. phagocytes

Question 11

Humoral response

Answer 11

B Cells, clonal selection and the production of monoclonal antibodies

Question 12

Primary immune response

Answer 12

When antigen enters body for the first time
Slow - not many B Cells that can make necessary antibody
Eventually enough antibody produced
Sufferer shows symptoms of disease
Exposure to antigen means T and B cells produce memory cells
Memory cells remain in body for a long time
Memory T cells remember specific antigen
Memory B cells remember specific antibodies
Person is now immune - system has ability to respond quickly to a second infection

Question 13

Secondary Immune Response

Answer 13

familiar pathogen enters body
Response is quicker and stronger
Clonal selection occurs faster
Memory B cells activated and divide into plasma cells that produce correct antibody to antigen
Memory T cells activated and divide into correct type of T cells to kill the pathogen
Response kills pathogen before symptoms occur