IB Biology Review Immune System Immune System Vocab Pathogen

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IB Biology Review

• Immune System

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Immune System Vocab

• Pathogen
• An organism or virus that causes a disease
• Antigen
• Any foreign macromolecule (either proteins,
  polysaccharides or structures on the surface of
  bacteria) that triggers an immune response
• Antibody
• Antibodies are proteins that bind to particular
  antigens and mark them for elimination from the
  body
• Antibiotics
• Any substance that is able to kill or inhibit a
  microorganism such as bacteria

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Passive versus Active Immunity

• Passive immunity is due to the acquisition of
  antibodies from another source
• Such as
• when a developing fetus acquires antibodies from
  its mother
• when they are artificially injected into a person
• Active immunity is when antibodies are produced
  by the person themselves after his or her immune
  system is triggered by antigens

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Immune System Vocab cont.

• Virus
• An infective agent consisting of a protein coat
  surrounding an RNA or DNA core
• Are not cells and do not possess membranes or
  organelles.
• They cannot manufacture their own proteins and
  must invade living cells to take over their
  protein production machinery
• Leucocytes
• White blood cells
• Phagocytic leucocytes
• Specialized white blood cells that engulf
  foreign/invading pathogens and destroy them

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Different Types of Leucocytes

• The only ones we need to know are monocytes and
  macrophages, and lymphocytes

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Why are antibiotics effective against bacteria,
but not viruses?

• Most antibiotics dont kill bacteria
• Antibiotics disrupt their reproduction (binary
  fission) by preventing formation of the bacterial
  cell wall in the daughter cells (a part of the
  cells metabolism)
• Since viruses arent cells and dont produce cell
  walls, antibiotics are not effective against them

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What are the different components of the immune
system?

• Skin
• Mucous membranes
• Phagocytic leukocytes
• Antibodies

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Skin and Mucous Membranes

• These are a form of external defense preventing
  pathogens from entering the body
• Skin forms a physical barrier
• Mucous membranes surround invading pathogens
• Body senses excess mucous, induces coughing
• Coughing expels the mucous and the trapped
  pathogen

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Phagocytic Leucocytes

• A type of white blood cell
• Float around the body in blood
• Phagocyte surrounds the pathogen by endocytosis
• A vacuole containing the pathogen travels to a
  lysosome
• The membranes of the vacuole and lysosome fuse
• Digestive enzymes in the lysosome destroy the
  pathogen
• The pathogen debris is released by exocytosis

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Phagocytic Leucocyte Diagram
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Antibodies

• Proteins that recognize one kind of antigen
• Similar to enzymes (lock and key)
• Lock and key called epitope
• React by binding to the antigen
• Destroys antigen
• Or
• Inactivates antigen

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Antibody Production

• Pathogen is in the body
• Phagocytic leucocytes called macrophages ingest
  the pathogens
• Phagocytes present the antigens from the
  pathogens on their cell surface.
• T-helper cells (another type of leucocyte that is
  specific to that antigen) bind to the antigen
  presented by the macrophages and are
  activated/stimulated
• Meanwhile, B-cells bind to the antigen, and
  present the antigen as the phagocytes did

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Antibody Production cont.

• The activated T-helper cells then bind to B-cells
  and activate them
• This triggers the B-cells to undergo mitosis to
  form memory cells and plasma cells
• Short-lived Plasma B-cells secrete antibodies
  quickly that neutralize the pathogen
• Memory B-cells stay in the blood for a long time
  and enable a more rapid response by the immune
  system if the same pathogen invades in the future

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HL Only Monoclonal Antibodies

• Monoclonal antibodies
• large quantities of a single type of antibody
• produced in a laboratory
• Hybridoma cell
• memory B cell fused with a tumor cell
• divides uncontrollably, producing a large amount
  of antibodies

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HL Only Monoclonal Antibody Production

• 1. Antigens that correspond to a desired antibody
  are injected into an animal
• 2. B-cells producing the desired antibody are
  harvested
• 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 the
  antibodies they produce are extracted and
  purified

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HL Only Application of Monoclonal Antibodies
Rabies Treatment

• 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
• At the same time, the person's body begins making
  its own antibodies
• Triggers two-fold immune response
• Passive through injection
• Active through bodys production

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HL Only Application of Monoclonal Antibodies
Malaria Diagnosis

• 1. Monoclonal antibodies are made to bind to
  antigens in malarial parasites
• 2. A test plate is covered with antibodies
• 3. The sample is left on the plate long enough
  for malaria antigens (if present) to bind to
  antibodies
• 4. The sample is rinsed off
• Any bound antigens are detected using more
  monoclonal antibodies with attached
  color-changing enzyme

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HL Only Challenge and Response, Clonal
Selection, and Memory Cells

• B-cells make antibodies
• The immune system can make 1015 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 produces 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

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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
  response and prevents any ill effects

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HL Only Benefits and Dangers of Vaccines

• Benefits
• prevent disease and epidemics
• results in a healthier society
• reduces long-term medical costs
• speed up the body's response to a future disease
  by memory B-cells
• Dangers
• possible allergic reactions
• danger of side-effects

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HIV and the Immune System

• HIV virus kills Helper T-cells
• Helper T-Cells tell B-cells there is a pathogen
• Immune system cannot mount an effective defense
  against invading pathogens
• Patients then succumb to secondary infections

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Blood Clotting

• Damaged cells in the blood vessel release
  compounds called clotting factors
• These factors trigger the formation of the
  enzyme thrombin
• Thrombin catalyzes the conversion of soluble
  fibrinogen in the blood to the fibrous protein
  fibrin
• Fibrin forms threads which create an interwoven
  net
• Platelets and blood cells get caught in the net
  and plug up the wound

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Blood Clotting Diagram
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1. Which is not true of active immunity? (1
mark)
IB Exam Question

• A. It can be produced by exposure to a disease
  causing organism.
• B. It can be produced artificially.
• C. It can be produced by a virus.
• D. It can be transferred via the colostrum.
• Correct answer D
• If youve never heard of it, its probably a
  trick question!

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2. Describe how human skin and mucous membranes
act as barriers to pathogens.(4 marks)
IB Exam Question

• To receive full marks, responses must have two
  answers for each.
• Skin
• lower pH / acid to keep bacteria from growing /
  chemical barrier
• fatty acids / waxes antimicrobial
• physical barrier to prevent entry / dry skin
  inhibits bacterial growths
• bacteria on skin / mucous membranes prevent other
  bacteria from growing
• antimicrobial / lysozyme in sweat and saliva
  (mucous membrane) to keep bacterial growth in
  check
• Mucous membranes
• mucous traps bacteria / sticky / mucus slightly
  acidic i.e. vagina
• cilia sweep mucous up to be swallowed to kill
  bacteria
• contain macrophages / phagocytes

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3. Outline how phagocytic leucocytes ingest
pathogens in the blood and in body tissues.
IB Exam Question

• The phagocytic cell surround the pathogen by
  endocytosis
• A vacuole containing the pathogen travels to a
  lysosome and the membranes of the vacuole and
  lysosome fuse
• Digestive enzymes in the lysosome destroy the
  pathogen
• The pathogen debris is released by exocytosis

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4. Which of the following represents the correct
sequence of events when the body is responding to
a bacterial infection?
(1 mark)
IB Exam Question

• I. Antigen presentation by macrophages
• II. Activation of B-cells
• III. Activation of helper T-cells
• A. I, II, III
• B. I, III, II
• C. III, II, I
• D. II, III, I
• Correct answer B

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5. Explain antibody production.
IB Exam Question

• A vaccine is injected into body
• This vaccine contains killed / weakened pathogen
  or fragments of pathogens
• Phagocytic leucocytes called macrophages ingest
  the pathogens and present the antigens from the
  pathogens on their cell surface.
• Helper-T cells (another type of leucocyte that is
  specific to that antigen) bind to the antigen
  presented by the macrophages and are
  activated/stimulated
• Meanwhile, B-cells bind to the antigen, and
  present the antigen as the T cells did
• The activated T-helper cells then bind to B-cells
  and activate them
• This triggers the B-cells to undergo mitosis to
  form memory cells and plasma cells
• Short-lived Plasma B-cells secrete antibodies
  quickly that neutralize the pathogen
• Memory B-cells stay in the blood for a long time
  and enable a more rapid response by the immune
  system if the same pathogen invades in the future

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6. Which type of cell is responsible for
secondary immune responses to a pathogen?
(1 mark)
IB Exam Question

• A. Cytotoxic T-cells
• B. Phagocytes
• C. Macrophages
• D. Memory cells
• Correct answer D

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HL Only 7. Outline the principles of challenge
and response, clonal selection, and memory cells
as the basis of immunity.
IB Exam Question

• B-cells make antibodies
• The immune system can make 1015 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 produces 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

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8. Which type of immunity usually results from
vaccination? (1 mark)
IB Exam Question

• A. active, natural
• B. active, artificial
• C. passive, natural
• D. passive, artificial
• Correct answer B

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9. Discuss the benefits and dangers of
vaccination.
(8 marks)
IB Exam Question

• Benefits 5 max
• prevent disease
• eliminate diseases like smallpox
• prevent epidemics
• healthier society
• reduce medical cost
• disease free cattle / more food
• Dangers 3 max
• allergic reactions / anaphylactic shock
• weakened virus becomes virulent / causes the
  disease
• harmful side-effects

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10. Which curve shows the response of the immune
system to a vaccine, followed by an infection?

(1 mark)
IB Exam Question

• Correct answer B

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HL Only 11. Describe the production of
monoclonal antibodies along with one use of them
in diagnosis and one use in treatment.
IB Exam Question

• 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.

35
HL Only 11. Describe the production of
monoclonal antibodies along with one use of them
in diagnosis and one use in treatment. cont.
IB Exam Question

• 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.

36
12. Outline the effect of HIV on the immune
system.
IB Exam Question

• The HIV virus results in the death of Helper
  T-cells
• Therefore, the immune system of the infected
  individual cannot mount an effective defense
  against invading pathogens
• Patients can then succumb to secondary infections

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13. Describe the process of blood clotting.
IB Exam Question

• Damaged cells in the blood vessel release
  compounds called clotting factors
• These factors trigger the formation of the
  enzyme thrombin
• Thrombin catalyzes the conversion of soluble
  fibrinogen in the blood to the fibrous protein
  fibrin
• Fibrin forms threads which create an interwoven
  net. Platelets and blood cells get caught in the
  net and plug the open cut

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