The immune system

Question 1

Phagocytes - what does it do + process

Answer 1

Engulfs pathogens, phagocytes are the first cells to respond to an immue system trigger inside the body.
How they work:
- phagocyte recognises foriegn antigens on pathogen
- cytoplasm of the phagocyte engulfs pathogen
- pathogen now contained in a phagocytic vacuole in the phagocyte’s cytoplasm
- a lysosome fuses with the phagocytic vacuole + lysozymes break down pathogen.
- phagocyte presents the pathogens antigens on its surface to activate other immune system cells.

Question 2

Order of immune system response cells:

Answer 2

• phagocytes
• t cells
• b cells (which divide into plasma cells

Question 3

T-cells

Answer 3

Phagocytes activate T-cells - another type of white blood cell - it has receptor proteins on its surface which bind to complementary antigens presented by the phagocytes - which activates T cells
Different types of T cells activated:
- helper T-cells release chemical signals that activate + stimulate phagocytes + activate B cells
- Cytotoxic T-cells - kill abnormal and foriegn cells

Question 4

B-cells

Answer 4

T-cells activate B-cells, which divide into plasma cells

• they are covered in antibodies and these proteins bind to antigens to form antigen-antibody complex.
• when the antibody on the surface of B-cells meets complementary shaped antigen - it binds to it
• this + with substances releases from helper T-cells - activates B-cells - this is clonal selection.
• activated B-cell divides into plasma cells or become memory cells + circulate the blood stream - to be able to rapidly divide if reinfection occurs

Question 5

Plasma cells

Answer 5

They make more antibodies to a specific antigen

• they are identical B-cells + they secrete lots of antibodies (monoclonal antibodies)
• they bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes = clumping of pathogens = agglutination = phagocytes binding to the antibodies and engulfing many pathogens at once.