Defense  Against  Infec.ous  Disease  

IB  Bio  12  

Assessment  Statements Obj.

6.3.1 Define  pathogen.   1

6.3.2 Explain  why  an.bio.cs  are  effec.ve  against  bacteria  but  not  viruses.   3

6.3.3   Outline  the  role  of  skin  and  mucous  membranes  in  defense  against  pathogens.   2

6.3.4 Outline  how  phagocy.c  leucocytes  ingest  pathogens  in  the  blood  and  body  .ssues.   2

6.3.5 Dis6nguish  between  an#bodies  and  an#gens.   2

6.3.6 Explain  an.body  produc.on.   3

6.3.7 Outline  the  effects  of  HIV  on  the  immune  system.   2

6.3.8 Discuss  the  cause,  transmission  and  social  implica.ons  of  AIDS.   3

Assessment  statements  from:  Online  IB  Biology  Subject  Guide Command  terms:  hPp://i-­‐biology.net/ibdpbio/command-­‐terms/

Bacteria  •  Prokaryotes    (no  real  nucleus)  •  Divide  by  binary  fission

Can  cause:  •  Food  poisoning  (e.g.  Salmonella)  •  Ear  and  eye  infec.ons  •  Cholera,  diarrhea hPp://en.wikipedia.org/wiki/

File:Ericson_Type_II_Conjunc.vi.s.JPG

The  1918  flu  epidemic  killed  between  50  and  130  million  people.  hPp://en.wikipedia.org/wiki/1918_flu_pandemic

Viruses  •  Acellular  (non-­‐living?)  •  Need  a  ‘host’  cell  to  carry  out  func.ons  of  life,  including  reproduc.on  •  Can  have  DNA  or  RNA  •  Mutate,  evolve  and  recombine  quickly  

Cause:  •  Flu,  HIV/AIDS,  smallpox,  measles,  common  cold,  herpes,  ebola    

Fungi  •  Eukaryotes,  reproduce  with  spores    Cause:    •  Athlete’s  foot,  mould,  ringworm  •  Allergic  reac.ons  and  respiratory  problems  

Image  from:    hPp://en.wikipedia.org/wiki/Athlete's_foot

Protozoa  •  Simple  parasites    Cause:  •  Malaria  •  Leishmaniasis  •  Toxoplasmosis  

Leishmaniasis  image  from:    hPp://en.wikipedia.org/wiki/Leishmaniasis

Life  Cycle  of  Leishmania  

3  Main  Lines  of  Defense  

1)  Physical  barriers  –  Skin,  mucous  membranes  

2)  Non-­‐specific  immune  system  –  Phagocy.c  leukocytes  

3)  An.gen-­‐specific  immune  system  –  Lymphocytes  (e.g.  B-­‐cells,  T-­‐cells,  Killer  cells)  

hPp://apchute.com/lympha.c/inflam.html

Phagocy.c  Leucocytes “ea.ng  cell” “white  blood  cells”

Chemotaxis  (movement  in  response  to  chemicals)  aPracts  the  phagocytes  to  the  area  of  invasion  as  response  to:    •  proteins  produced  by  the  pathogen  •  phospholipids  released  by  damaged  cells    The  phagocyte  aPaches  to  the  pathogen’s  cell  surface  proteins  and  then  engulfs  it.  The  fluid  nature  of  the  plasma  membrane  allows  this  to  happen.      A  phagosome  forms.  This  is  a  vesicle  that  contains  the  pathogen.  Lysosomes  –  vesicles  of  diges.ve  enzymes  –  deposit  the  enzymes  into  the  phagosome.      The  diges.ve  enzymes  break  down  the  pathogen  and  the  waste  products  are  expelled  from  the  cell  by  exocytosis.  

Review  opportunity:    •  Plasma  membranes  and  vesicles  •  Membrane  fluidity  and  fusion  •  Endo-­‐  and  exo-­‐cytosis

Phagocy.c  Leucocytes card  sort  game:  order  the  images    &  outline  the  processes

Images  from:  hPp://highered.mcgraw-­‐hill.com/sites/0072495855/student_view0/chapter2/anima.on__phagocytosis.html