The Immune System

• What do foreign antigens trigger?

  An immune response
• What does each type of cell have on it?

  Molecules (including proteins) on its surface that identify that cell
• what do the molecules/proteins on the surface of cells enable the immune system to identify?

  Pathogens, Cells from other organisms of the same species, Abnormal body cells, Toxins
• What is an antigen?

  A protein that can generate an immune response when detected by the body
• Where are antigens usually found?

  On the surface of the cells
• What does the BODY USE ANTIGENS to IDENTIFY?

  Pathogens

  abnormal body cells

  toxins

  cells from other individuals of the same species
• what are pathogens?

  Microorganisms that cause disease
• Give examples of abnormal body cells?

  Cancerous or pathogen-infected body cells- which have abnormal antigens on their surface
• Give an example of a cell from other individuals of the same species which antigens would identify?

  Organ transplants
• What is a phagocyte aaka?

  macrophage
• What is a phagocyte?

  A type of white blood cell that carries out phagocytosis
• What is phagocytosis?

  Engulfment of pathogens
• Where are phagocytes found?

  In the blood and in tissues
• What are phagocytes the first cells to do?

  Respond to an immune system trigger in the body
• What do phagocytes do?

  Engulf pathogens
• How do phagocytes destroy a pathogen found in the blood-answer found from AQA mark scheme ?

  1. Engulfs the pathogen
  2. Forming vesicle and fuses with lysosome
  3. Enzymes digest/hydrolyse
• What is a T-cell aka?

  T-lymphocyte
• What cells do phagocytes activate?

  T-cells
• What is a T-cell a type of?

  White blood cell
• What do T-cells have?

  Receptor proteins on its surface
• What do the receptor proteins on the surface of T-cells do?

  Bind to complementary antigens presented to it by phagocytes. This ACTIVATES the T-cell
• What are the different types of T-cells?

  Helper T-cells

  Cytotoxic T-cells

  These respond in DIFFERENT WAYS
• How do helper T-cells respond?

  Release chemical signals that activate and stimulate phagocytes
• How do Cytotoxic T-cells respond?

  Kill abnormal and foreign cells
• What do helper T-cells also do?

  activate B-cells
• What do B-cells do?

  Secrete antibodies
• T-cells activate what?

  B-cells
• What are B-cells aka?

  B-lymphocytes
• What are B-cells a type of?

  white blood cell
• What are B-cells covered with?

  ANTIBODIES
• What are antibodies?


  Proteins that bind antigens to form an antigen-antibody complex
• What does each B-cell have?

  A different shaped antibody in its membrane, so different ones bind to different shaped antigens
• Why are antibodies important with the stimulation of phagocytosis (aqa q and answer)?

  Bind to antigen/are markers

  Antibodies use clumping/AGGLUTINATION
• How do B-cells work?

  1. When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it
  2. This, together with the substances released from helper T-cells, activates the B-cell. This process = CLONAL SELECTION
  3. The activated B-cell divides into PLASMA CELLS
• What do plasma cells do?

  make more antibodies to a specific antigen
• What are identical?

  plasma cells and B-cells (the plasma cells are clones of the B-cell)
• What do plasma cells do?

  Secrete lots of antibodies specific to the antigen

  = monoclonal antibodies
• What do the antibodies secreted by plasma cells do?

  Bind to the antigens on the surface of the pathogen to form many antigen-antibody complexes
• How does agglutination occur?

  • Antibodies have 2 binding sites so can bind to two pathogens at the same time
  • = Pathogens become clumped together = agglutination
• What happens after agglutination by the antibodies?

  Phagocytes bind to the agglutination and then they bind to the antibodies and phagocytose MANY pathogens at once.

  = the process leads to the destruction of pathogens carrying this antigen in the body