IB Biology Review

IB Biology Review Immune System

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

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

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

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

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

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

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

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

Phagocytic Leucocyte Diagram

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

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

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

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

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

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

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

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

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

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

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

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

Blood Clotting Diagram

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

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;

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

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

IB Exam Question 5. Explain antibody production. • 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

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

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

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

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;

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

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.

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.

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

IB Exam Question 13. Describe the process of 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 the open cut

IB Biology Review