IB Biology/Defense Against Infectious Disease

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Chapter 10: Defense Against Infectious Disease[edit]

Types of Defense[edit]

Describe the process of clotting.

  • Platelets are small fragments that circulate along with erythrocytes (red blood cells) and leukocytes (white blood cells) in blood plasma.
  1. Clotting process begins with the release of incomplete fragments of cells from the damaged tissue, resulting in the formation of thrombin.
  2. Thrombin converts fibrinogen (always in the bloodstream) into the fibrous protein fibrin.
  3. Fibrin captures red blood cells and immobilizes the fluid portion of the blood so as to provide the impetus for clotting.
  4. Blood becomes slightly solidified (similar to a gelatin-like substance) until...
  5. Platelets reach this fibrous mass and send out sticky extensions to each other.
  6. The platelets then contract, forcing out the liquid and scabbing over the wound!

Outline the principles of challenge and response, clonal selection, and memory cells as the basis of immunity.

  • B cells make antibodies.
  • The immune system can make 10^15 different types of antibodies (but not all at once).
  • A few of each type of B cell are produced and they wait until the body is infected with an antigen.
  • When this occurs, they multiply to form many clones; this is called Clonal Selection.
  • A clone of B cells can produce large amounts of antibodies quickly and give immunity to a disease, only after the immune system is challenged by a disease -- this is called the challenge and response system. The immune system needs to be "challenged" by a disease, usually in the form of an antigen present upon it, and then the immune system responds by producing a clone of "B" cells which produce large amounts of antibodies to fight and eliminate the pathogen.

Define active immunity, passive immunity, natural immunity, and artificial immunity.

  • Active immunity - Immunity due to antibody production by the organism following the invasion by pathogens.
  • Passive immunity - Immunity due to antibodies received from another organism which made them as a result of that particular organism's own active immunity.
  • Natural immunity - Immunity as the result of infection with a pathogen, as per the challenge and response method.
  • Artificial immunity - Immunity as the result of a vaccine which contains antibodies that are used to fight the pathogen.

Explain antibody production.

  1. Macrophages consume bacteria with antigen molecules in their membranes.
  2. Macrophages present these antigens on their membranes with the help of special protein structures.
  3. Helper T-cells come in contact with macrophages, pick up the antigens, and incorporate them into their own protein structures - this will allow them to present the antigens to B-cells. This also causes the activation of the Helper t-cells.
  4. Activated helper-T-cells activate B-cells by passing their antigen to B-cell receptors.
  5. The B-cells then divide to form clones of antibody-secreting plasma cells and memory cells.

State that cytotoxic T-cells destroy cancer cells and body cells infected with viruses. Cytotoxic T-cells destroy cancer cells and body cells infected with viruses.

Describe the production of monoclonal antibodies along with one use of them in diagnosis and one use in treatment.

  • Monoclonal antibodies - large quantities of a single type of antibody, produced using the procedure outlined below:


  1. Antigens that correspond to a desired antibody are injected into an animal.
  2. B-cells producing the desired antibody are extracted.
  3. Tumor cells are obtained from another source (tumor cells grow and divide endlessly).
  4. B-cells are fused with tumor cells, producing hybridoma cells that divide endlessly, providing the desired antibodies.
  5. The hybridoma cells are cultured and antibodies they produce are extracted and purified.
  • Treatment of rabies
  • Rabies usually causes death in humans before the immune system can control it.
  • Injecting monoclonal antibodies when a person gets infected will control the virus and at the same time, the person's body begins making its own antibodies.
  • Diagnosis of malaria
  1. Monoclonal antibodies are made to bind to antigens in malarial parasites.
  2. A test plate is covered with antibodies.
  3. The sample to be tested is left on the plate long enough for malaria antigens (if present) to bind to antibodies.
  4. The sample is rinsed off and any bound antigens are detected using more monoclonal antibodies with attached color-changing enzyme.
  • Color-changing enzyme can be used to measure the level of infection and distinguish between different strains of malaria.

Production should be limited to the fusion of tumour and B-cells and their subsequent proliferation and production of antibodies. Detection of antibodies to HIV is one example in diagnosis. Others are detection of a specific cardiac isoenzyme in suspected cases of heart attack and detection of HCG in pregnancy test kits. Examples of the use of these antibodies for treatment include targeting of cancer cells with drugs attached to monoclonal antibodies, emergency treatment of rabies or cancer, blood and tissue tying for transplant compatability and purification of industrially made interferon.

Outline the principle of vaccination.

  • A weakened or dead version of a pathogen is injected into the body, causing the immune system to mount a primary response.
  • This results in the production of B memory cells.
  • The B-cells "remember" the antibodies to produce in response to the pathogen.
  • When the real pathogen strikes, a secondary response occurs, aided by the memory cell production of pathogen-specific antibodies.
  • This response is much stronger than the primary repsonse and prevents any ill effects.

Distinguish between polyclonal and monoclonal antibodies

  • Polyclonal antibodies
  • A mixed population of antibodies with multiple responses. They recognize multiple epitopes (separate antigen markers - areas on the surface of a given protein macromolecule that are in turn recognized by the immune system).
  • Produced by injecting animals with a specific antigen. A series of antibodies are produced in response to a variety of different sites on the antigen.
  • Monoclonal antibodies
  • Single, specific antibodies with only one response (to just one antigen).
  • See above for production.

Discuss the benefits and dangers of vaccination against bacterial and viral infection, including the MMR vaccine (measles, mumps, and rubella) and two other examples.

  • Benefits of vaccination
  • Some diseases, such as small pox, can be eradicated.
  • Deaths can be prevented, ex. from measles.
  • Long-term disabilities can be prevented
  • Rubella in pregnant women can lead to birth defects
  • Mumps can cause infertility in men.
  • Dangers of vaccination
  • Immunity developed after vaccination may not be as effective as immunity developed in response to the actual disease.
  • Dangers of side effects of some vaccines include:
  • Whooping cough, vaccine can cause brain damage.
  • Pregnant women, cancer patients, and others can be harmed by cross-infection from people vaccinated with the live virus, ex. smallpox vaccine.