1. IB Biology Review
Immune System

2. Immune System Vocab Pathogen Antigen Antibody Antibiotics
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

3. 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

4. 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

5. Different Types of Leucocytes
The only ones we need to know are monocytes and macrophages, and lymphocytes

6. Why are antibiotics effective against bacteria, but not viruses?
Most antibiotics don’t kill bacteria
Antibiotics disrupt their reproduction (binary fission) by preventing formation of the bacterial cell wall in the “daughter cells” (a part of the cell’s metabolism)
Since viruses aren’t cells and don’t produce cell walls, antibiotics are not effective against them

7. What are the different components of the immune system?
Skin
Mucous membranes
Phagocytic leukocytes
Antibodies

8. 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

9. 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

10. Phagocytic Leucocyte Diagram

11. 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

12. 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

13. 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

14. HL Only: 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

15. 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

16. 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 body’s production

17. 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

18. 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

19. 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

20. HL Only: Benefits and Dangers of Vaccines
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

21. 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

22. 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

23. Blood Clotting Diagram

24. 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 you’ve never heard of it, it’s probably a trick question!

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

26. The phagocytic cell surround the pathogen by endocytosis
IB Exam Question
3. Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.
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

27. I. Antigen presentation by macrophages II. Activation of B-cells
IB Exam Question
4. Which of the following represents the correct sequence of events when the body is responding to a bacterial infection? (1 mark)
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

28. 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

29. A. Cytotoxic T-cells B. Phagocytes C. Macrophages D. Memory cells
IB Exam Question
6. Which type of cell is responsible for secondary immune responses to a pathogen? (1 mark)
A. Cytotoxic T-cells
B. Phagocytes
C. Macrophages
D. Memory cells
Correct answer: D

30. B-cells make antibodies
IB Exam Question
HL Only: 7. 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 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

31. 8. Which type of immunity usually results from vaccination? (1 mark)
IB Exam Question
8. Which type of immunity usually results from vaccination? (1 mark)
A. active, natural
B. active, artificial
C. passive, natural
D. passive, artificial
Correct answer: B

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

33. IB Exam Question
10. Which curve shows the response of the immune system to a vaccine, followed by an infection? (1 mark)
Correct answer: B

34. IB Exam Question
HL Only: 11. 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.

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

37. 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