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IBDP Biology: Defense Against Diseases

Topic 6.3: Disease Defenses

· Biology,disease,IBDP BIOLOGY

How does the body protect itself from foreign substances? In this IBDP Biology blog we will learn:

  • The definition of a Pathogen
  • The three modes of defenses
  • Blood clot preventations
  • What are antibiotics and how are they made

Pathogen and Defences

Definition: An organism or virus that cause a disease (viruses, bacteria, protozoa, fungi and worms etc)

Primary Defense: 

1. Skin

  • Continuous
  •  (hard to find an opening)
  • Many layers- Outer layers are tough providing a physical barrier
  • Dry
  • pH
  •  is not favourable to pathogen- Sebaceous glands secrete lactic acid and fatty acids making skin surface more acidic
  • Lysozomes

 - enzymes breakdown pathogens

  • Natural organisms - competitive exclusion by non-harmful microbes

2. Mucous Membranes

  • Sticky 
  • mucus
  •  traps invaders
  • pH
  •  not favourable to pathogens
  • Lysozome - enzymes breakdown pathogens
  • Natural organisms - competitve exclusion by non-harmful microbes

Secondary Defense (NON SPECIFIC)

1. Phagocytes

  •  Phagocytes ingest pathogens by 
  • endocytosis
  • Pathogens are then 
  • killed and digested by enzymes
  •  from Lysosomes
  • Antigens on the surfaces of cells and viruses allow for recognition
  • If a cell is 

not recognised - Phagocyte engulfs and ingests the pathogen by phagocytosis and lysosomes digests the pathogens

Non-specific Immunity:  Does not distinguish between pathogens (ingests any pathogen)

  • Phagocytes are in the blood and squeeze out through the walls of capiliaries and move through tissues to infection sites
  • If Phagocyte response is not enough and infection spreads - Lymphocytes are called in to help 

Tertiary Defense (SPECIFIC IMMUNITY)

Antigens: Molecule found on cell or virus surface that causes antibody formation

Antibodies: Globular protein that recognizes a specific antigen and binds to it as part of an immune response

Plasma cells: Clones of identical cells

Memory Cells: Quickly reproduce to form plasma cells 

  • Antibodies bind to Antigens 

and are specific to Antigens

  • Antigens 

stimulate the production of Antibodies

  • Each Lymphocyte can only make 

one type of antibody. Each Lymphocyte puts some of the antibodies it can make on the cell surface membrane

  • When a pathogen enters its antigen binds to the antibody of that Lymphocyte
  • This makes the Lymphocyte active and 

divides by mitosis and produces 

  • Plasma cells produce a lot of the 

same antibody

  • Antibody binds to the antigens on the surface of the pathogens and stimulates its destruction
  • After the infection most Lymphocytes dissapear but some are kept as 

memory cells

  • if a pathogen with the same antigen is encountered again 

Antibody Production

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Humans have different types of B lymphocytes, which produce a relatively small number of one type of antibody each. However, our immune response can produce more antibodies:

1. Antigen is identified.

2. B lymphocyte is identifies to produce an antibody which will bind to the antigen.

3. B lymphocytes clone themselves (mitosis) to increase in number.

4. The “army” begins antibody production.

5. Antibodies eventually find their antigen match.

6. Antibodies eliminate the pathogen.

7. Clones B lymphocytes remain and give immunity (memory cells).Many different Lymphocytes exist)

And we're done!

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References

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2Fbrown-friends-intense-stickers309904018110618952%2F&psig=AOvVaw0MuRNvxpCB4irWgHaj6y2i&ust=1624951834450000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCIi1iLrnufECFQAAAAAdAAAAABAD

https://www.google.com/url?sa=i&url=https%3A%2F%2Fbiology-igcse.weebly.com%2Fimmune-system---antibody-tissuerejection.html&psig=AOvVaw1IYYDpPCNIK1rb6ZHO4jln&ust=1624951377415000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNivrODlufECFQAAAAAdAAAAABAD

Written by Venetia (Biology)

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