Immunity

Question 1

Examples of plasma proteins

Answer 1

Serum albumin
Hormones
Antibodies
fibrin
fibrinogen
thrombin
clotting factors

Question 2

Phagocytes

Answer 2

Engulf by endocytosis/exocytosis and digest bacteria, can squeeze through gaps of the capillary wall and escape from the bloodstream. Confer non-specific immunity. The vesicle containing the pathogen is called the phagosome. The pathogen is digested by hydrolytic enzymes from the lysosomes. The remains are expelled by exocytosis.

Question 3

Platelets

Answer 3

cell fragments-play a role in bloo clotting

Question 4

Pathogen

Answer 4

An organism or virus that causes disease

Question 5

Species-specific pathogens

Answer 5

Infect members of a single species eg. polio

Question 6

Pathogens that cross species barriers

Answer 6

A disease that can be passed to humans from other animals-emerging health concern. i.e. rabies

Question 7

Antigen

Answer 7

Any chemical substance that stimulates an immune response/antibody production. Often proteins or polysaccharides on the surface of pathogens, cancer cells eg.

Question 8

Unique molecules on the cell surface of viruses

Answer 8

Every species has unique surface molecules. Viruses are not living organisms and are not composed of cells. But, their surface is a protein coat called the capsid which has unique molecules. The capsid of some viruses is enveloped in a membrane taken from the plasma membrane of the host cell.

Question 9

Uses of unique surface molecules

Answer 9

-viruses recognise and bind to the host using molecules on the host’s cells surface
-organisms recognise their own cells and cell types using surface molecules
-organisms recognise foreign cells and viruses by surface molecules that are not present in that organism-trigger the production of antibodies

Question 10

ABO blood group system

Answer 10

Based on the presence/absence of certain antigens in the membrane of RBCs. The O, A and B antigens are different versions of the same glycoproteins. The O antigen is always present

Question 11

A antigen

Answer 11

Formed by addition of an N-acetyl-galactosamine molecules to O antigen

Question 12

B antigen

Answer 12

Addition of a galactose molecule to O antigen

Question 13

Problems with blood transfusions

Answer 13

Mismatches between donor and recipient can lead to an immune response in the recipient if the recipient does not possess a glycoprotein, it produces antibodies against it. The antibodies causes agglutination of RBCs followed by hemolysis

Question 14

Skin

Answer 14

Provides a physical barrier
Sebaceous glands secrete sebum which contains lipids, lactic acid and fatty acids which lowers the pH of the skin thus preventing bacterial growth- chemical barrier

Question 15

Mucous membranes

Answer 15

-thin, soft areas of skin found in the nose, trachea
- secrete mucus
-mucus has anti-bacterial enzyme lysozyme
-mucus traps pathogens and particles, which are then swallowed or expelled

Question 16

Blood clotting

Answer 16

1. When the skin is cut, blood vessels are injured and bleed.
2. The blood in the wound turns to a semi-solid gel which prevents both further loss of blood and entry of pathogens. This is clotting and is promoted by platelets.
3. Clotting starts when platelets aggregate at the site to form a plug and clotting factors are released. Clotting involves a cascade of reactions: the product of each reaction is the catalyst for the next.
4. In the last step of the cascade, the enzyme thrombin is produced and this converts the soluble protein fibrinogen to the insoluble fibrin.
5. Fibrin forms a mesh which traps blood cells and forms a scab. Clots can also happen in coronary arteries when the fatty plaque deposits can cause a heart attack

Question 17

Immune response

Answer 17

Production of antibodies by B lymphocytes. Each B lymphocyte produces one type of antibody. Antibodies are proteins that recognise specific antigens and bind to them- specific immunity

Question 18

Order of antibody production

Answer 18

1. Activation of helper T cells
2. Activation of B cells
3. Production of plasma cells
4. Production of memory cells

Question 19

Activation of helper T cells

Answer 19

Macrophages engulf the pathogen, digest it and display antigens from it in their plasma membrane. Antigens on the macrophage membrane are attached to MHC molecules. Helper T-cells each have an antibody-like receptor protein in their plasma membrane which binds to one specific antigen displayed by the macrophage. When the antigen binds, the helper T lymphocyte is activated

Question 20

Activation of B cells

Answer 20

Inactive B lymphocytes have antibodies on their plasma membrane. If the antibodies match an antigen, the antigen binds to the antibody. An activated helper T lymphocyte with receptors for the same antigen can then bind to the B lymphocyte. The activated helper T lymphocyte sends a signal to the B lymphocyte, activating it

Question 21

Production of plasma cells
(clonal selection)

Answer 21

The activated B lymphocytes divide by mitosis to form a clone of identical plasma cells-clonal selection. Plasma cells are mature activated B lymphocytes that produce large quantities of the same specific antibody and secrete it in the plasma. Plasma cells have an extensive network of rER to synthesise large amounts of an antibody to be secreted by exocytosis.

Question 22

Production of memory cells

Answer 22

Most of the clone of B lymphocyte become active plasma cells, but a small number become memory cells. Some T cells also become memory cells. These memory cells remain inactive, but they are long-lived and persist after the activated cells and antibodies produced to fight the disease have disappeared. Memory cells repsond quickly: they become active and reproduce quickly to form a clone of plasma cells producing the specific antibody-long-term immunity

Question 23

Structure of antibodies(immunoglobins)

Answer 23

Have a hypervariable region and a constant region. The tips of the hypervariable region bind the antigen. The constant region is the part of the molecule that aids the destruction of the pathogen

Question 24

Different mechanisms used by the constant region to destroy a pathogen

Answer 24

-Making pathogens more recognisable to phagocytes so they are more readily engulfed
-binding to the surface of a pathogen and activating the complement system. Activation of the complement cascade leads to formation of pores in the membrane and lysis of the pathogen cell.
-Sticking pathogens together so they cannot enter host cells
-neutralising toxins produced by pathogens
-preventing viruses from docking to host cells

Question 25

Vaccination

Answer 25

Vaccines contain weakened or killed forms of the pathogen or the antigen. They are injected. The antigens in the vaccine cause the primary immune response resulting in low antibody production and production of memory cells. When exposed to the actual pathogen the memory cells trigger a more potent secondary immune response which causes faster and greater antibody production.

Question 26

Smallpox

Answer 26

Smallpox was the first disease for which a vaccine was tested on humans. Jenner infected an 8-year-old boy with cowpox using pus from a blister of an infected milkmaid. The boy recovered. He then infected the boy with smallpox and found that he was immune. The antibodies produced against cowpox also gave immunity to smallpox.

Question 27

Reasons why Jenner’s experiment is considered as ethically unacceptable

Answer 27

involved deliberate infection with an extremely virulent strain
below age of consent
no lab work nor animal studies
no tests for potential side-effects

Question 28

Monoclonal antibodies

Answer 28

Purified antibodies that are produced by a single clone of hybridoma cells, so are identical. Highly specific to one antigen

Question 29

Production of monoclonal antibodies

Answer 29

Antigens corresponding to a desired antibody are injected into a mouse. Plasma B cells producing the desired antibody are extracted from the animal’s spleen. Tumour cells called myeloma cells are obtained from a culture. These cells grow and divide endlessly. The antibody-producing plasma cells are fused with the tumour cells to produce hybridoma cells. Hybridoma cells are cultured in a fermenter. They divide endlessly to form a clone which secretes huge amounts of one specific type of monoclonal antibody. The antibodies are extracted and purified

Question 30

Uses of monoclonal antibodies

Answer 30

Test kits for pregnancy, malaria, HIV, antibodies for injection into rabies victim

Question 31

Pregnancy test use of monoclonal antibodies

Answer 31

Pregnancy tests employ monoclonal antibodies to hCG.The urine of pregnant women uniquely contains hCG a protein secreted by the developing embryo and later by the placenta

Question 32

Active immunity

Answer 32

The individual is exposed to the antigen, antibodies are produced by the organism itself and memory cells are formed.

Through encountering the pathogen itself or by vaccination

Question 33

Passive immunity

Answer 33

An organism receives antibodies from an external source
Through breast milk or by injection of antibodies

Question 34

Allergen

Answer 34

A substance in the environment that triggers an immune response although it is normally harmless.

Question 35

Allergy

Answer 35

Reaction by the immune system to such substances- a severe systemic allergic reaction is called anaphylaxis and can be fatal.

Question 36

Histamine

Answer 36

Causes the symptoms associated with an allergic reaction. It causes small blood vessels in the infected area to dilate and increase permeability.

Question 37

Types of WBCs that secrete histamine

Answer 37

-Basophils: a type of WBC that circulate in the blood
-Mast cells: similar to basophils but are found in connective tissue.

Question 38

Symptoms associated with allergies

Answer 38

Tissue inflammation, itching, mucus secretion, sneezing

Question 39

Human Immunodeficiency virus

Answer 39

Has RNA as genetic material. Infects helper T lymphocytes. Results in gradual destruction of lymphocytes and progressive decrease in antibody production. Over time antibody production becomes very ineffective and this can lead to AIDS. AIDS causes a person to be susceptible to many other infectious diseases which would be fought off by a healthy immune system

Question 40

AIDS

Answer 40

An accumulation of opportunistic diseases

Question 41

HIV transmission

Answer 41

Blood transfusion, sexual intercourse, sharing hypodermic needles, from mother to baby

Question 42

Antibiotics

Answer 42

Chemicals that inhibit the growth of bacteria. They block processes which only occur in prokaryotes eg. cell wall formation, bacterial DNA replication. Produced by saprotrophic fungi. Some strains of bacteria have acquired resistance to one or more antibiotics.

Question 43

Reasons why antibiotics cannot treat viral infections

Answer 43

Viruses are non-living. They lack a metabolism and rely on the metabolic pathways of the host to carry out their processes and to reproduce.

Question 44

Measures to minimise antibiotic resistance

Answer 44

No antibiotic prescription for non-serious cases, high standards of hygiene at hospitals, no usage of antibiotics by farmers

Question 45

Testing penicillin

Answer 45

Penicillin was discovered in the fungus Penicillium by Alexander Fleming. Florey and Chain developed a method to produce penicillin from the fungus in the lab and performed experiments. They infected eight mice with bacteria that causes pneumonia. Four were given the antibiotic while the others did not. The four untreated died and the rest survived. They tested it on a human patient and after 4 days of treatment he improved.