4.1 Disease And The Immune System

Question 1

Name 4 groups of pathogen that can cause disease.

Answer 1

Bacteria
Virus
Protocista
Fungi

Question 2

List three bacterial diseases and their methods of transportation.

Answer 2

Tuberculosis - airborne droplets (human)
Meningitis - airborne droplets (human)
Ring rot - direct contact (plant)

Question 3

List three viral infections and their methods of transportation.

Answer 3

Influenza - airborne droplets (human)
HIV / AIDS - transfer of bodily fluids (human)
TMV - contact of leaves or vectors (plant)

Question 4

List two protocist infections and their methods of transportation.

Answer 4

Malaria - female mosquitos (human)
Late blight - spores (plant)

Question 5

How are communicable diseases pathogens transmitted directly ?

Answer 5

Inhalation of droplets
Skin to skin contact / exchange of fluids
Penetrate skin actively using enzymes / through wounds.

Question 6

How are communicable diseases transmitted indirectly ?

Answer 6

Consumption of contaminated food / drink
Vectors
Spores

Question 7

How do living conditions affect disease transmission ?

Answer 7

Overcrowding increases direct transmission
Climate determines what pathogens can survive
Social factors influence how quickly people are treated.

Question 8

Name 3 physical barriers to pathogen entry in plants.

Answer 8

Cellulose cell wall
Lignified layer
Waxy upper cuticle

Question 9

Describe 2 mechanical responses to infection in plants.

Answer 9

Guard cells close stomata
The polysaccharide callose is produced & placed between the cell wall and plasma membrane to increase entry distance.

Question 10

What is necrosis ?

Answer 10

Injury of a plant activates intracellular enzymes that kill cells near site of infection to prevent spread

Question 11

How do hydrolytic enzymes act as chemical defences in plants ?

Answer 11

Hydrolytic enzymes are found in the central vacuole and break down cell walls of invading organisms.

Question 12

How do Terpenoids act as chemical defences in plants ?

Answer 12

Terpenoids are oils that act as antibacterials, killing bacteria.

Question 13

How do Phenols act as chemical defences in plants ?

Answer 13

Phenols inhibit insects from attacking by interfering with digestion

Question 14

How do alkaloids act as chemical defences in plants ?

Answer 14

Alkaloids deter herbivores from feeding as they taste bitter.

Question 15

How do defensins act as a chemical defence in plants ?

Answer 15

Defensins inhibit transport channels of infected cells.

Question 16

Name 5 barriers to pathogen infection in humans

Answer 16

Keratin layer in skin
Blood clotting prevents pathogen entry through wounds
HCl in stomach kills bacteria
Beneficial bacteria in gut and skin provides competition
Mucous membranes trap pathogens

Question 17

What are expulsive reflexes ?

Answer 17

The body attempting to force foreign substances out
•Irritation of nostrils cause sneezing
•Irritation of of ciliated epithelial cells in lungs causes coughing

Question 18

Name 4 ways the nonspecific immune system responds to infection.

Answer 18

•Inflammation
•Phagocytosis
•Digestive action of lysozymes
•Production of interferon (antiviral agent)

Question 19

Outline the process inflammation.

Answer 19

Damaged tissues’ mast cells release histamines causing vasodilation
Blood flow and permeability of blood vessels increases
The mast cells also produce cytokines, which attract phagocytes to the effected area to undergo phagocytosis.

Question 20

How does blood clotting occur?

Answer 20

Blood platelets form plug and release chemicals that enhance plugging (thromboplastin)
Thromboplastin & CA2+ + Prothrombin-> Thrombin
Thrombin is an active enzyme which can now catalyse the following reaction :
(Thrombin +) Fibrinogen -> Fibrin
Fibrinogen is soluble, Fibrin is not
Fibrin makes a mesh which traps RBCs creating a thrombus (blood clot).

Question 21

Name the 2 types of white blood cells involved in phagocytosis.

Answer 21

Neutrophils
Macrophages (can become APCs)

Question 22

How does phagocytosis destroy pathogens ?

Answer 22

•Phagocyte moves towards pathogen which may have been marked by opsonins
•Phagocyte engulfs pathogen via endocytosis to form phagosome
•Phagosome uses lysosome to ingest pathogen

Question 23

Explain the role of antigen presenting cells (APCs).

Answer 23

•Macrophage displays antigen on its surface after pathogen is ingested
•Enhances recognition by Tʜ cells
•Secrete cytokines that are involved in stimulating specific immune response.

Question 24

What are lysozymes ?

Answer 24

The digestive enzyme found in lysosomes as well as tears and mucus
They damage bacterial cells walls

Question 25

Outline how to prepare a blood smear

Answer 25

Smear a drop of blood onto a slide using a spreader at 45• Add leishman stain then a buffer Rinse

Question 26

Name the two types of specific immune response.

Answer 26

Cell mediated Humoral

Question 27

Outline the process of cell mediated response.

Answer 27

*Complementary Tʜ cells bind to the foreign antigen on the APC *Cell signalling via secretion of interleukins stimulates : *a) Clonal expansion of Tʜ cells to become memory cells (humoral response) *b) Clonal expansion of cytotoxic T cells to secrete the enzyme perforin to destroy infected cells.

Question 28

Outline the process of humoral response.

Answer 28

*Complementary Tʜ lymphocytes bind to foreign antigen on APC cells *Cytokines released by Th lymphocytes that stimulate Clonal expansion of complementary B lymphocytes *B lymphocytes differentiate into plasma cells *Plasma cells secrete antibodies with complementary variable region to antigen

Question 29

Describe the structure and function of B and T lymphocytes.

Answer 29

Both have many specific receptors on surface B cells differentiate into plasma cells and produce antibodies There are 3 types of T cell: T helpers secrete cytokines (stimulate cells to move towards site of injury/disease) T killers secrete perforin (creates pore in target cells) T regulators suppress the other two cells to prevent autoimmune disease

Question 30

What is an antibody ? Describe / draw it’s structure.

Answer 30

They are proteins secreted by plasma cells Quaternary structure : 2 ‘light chains’ held by disulphide bridges to two ‘heavy chains’ The binding sites of variable regions of the light chains have specific tertiary structure to an antigen The rest of the molecule is known as the constant region.

Question 31

How do antibodies lead to the destruction of a pathogen ?

Answer 31

*Agglutinins form antigen-antibody complexes to enhance phagocytosis by making pathogens clump together *Opsonin antibodies can attach to bacteria making them readily identifiable to phagocytes. Antitoxins make toxins insoluble.

Question 32

What are memory cells ?

Answer 32

Specialised Tʜ / B cells produced via the primary immune response Remain in low levels in the blood Can divide very rapidly by mitosis if organism encounters the same pathogen again

Question 33

Contrast the primary and secondary immune response

Answer 33

Secondary response has: A faster rate of antibody production Shorter time lag between exposure and antibody production Higher conc or antibodies Antibody remain higher after secondary response Pathogen typically destroyed before symptoms occur.

Question 34

Contrast and compare passive and active immunity.

Answer 34

•Passive has no memory cells while active does •Passive is immediate while active requires time for synthesis •Passive has antibodies from external source and active has lymphocytes produce antibodies •Passive requires no direct contact with pathogen while active requires contact.

Question 35

Give examples of passive and active immunity.

Answer 35

Passive natural - antibodies in breast milk Passive artificial - blood transfusion with antibodies Active natural - humoral response to infection Active artificial - vaccination.

Question 36

Define autoimmune diseases, give examples.

Answer 36

When the immune system produces antibodies that target its own tissues Eg. HIV and arthritis.

Question 37

Explain the principles of vaccination.

Answer 37

•Vaccine contains dead/inactive form of pathogen •This triggers primary immune response •B lymphocytes then become memory cells, allowing for the secondary response to be rapid •Upon reinfection the pathogen can now be destroyed before symptoms.

Question 38

Define endemic and epidemic ?

Answer 38

Endemic : disease occurs routinely in an area Epidemic : temporary rapid increase in disease in an area

Question 39

What role does vaccination play in preventing epidemics ?

Answer 39

•Vaccination of a high percentage of a population reduces the available carriers of a pathogen, resulting in herd immunity

Question 40

List some possible natural sources of medicine.

Answer 40

•Microorganisms •Fungi •Plants •This is an important reason to maintain biodiversity as it means new sources may be discovered.

Question 41

What is personalised medicine and synthetic biology ?

Answer 41

Personalised medicine : observing the genome of an individual to predict their response to disease, and the best prescription Synthetic biology : engineering that targets biological processes.

Question 42

What are the benefits of using antibiotics to treat bacterial infections? How do they do this?

Answer 42

Effectively reduce the population of bacteria by : Preventing protein / nucleic acid synthesis Preventing formation of peptidoglycan cell walls.

Question 43

What are the risks of using antibiotics to treat bacterial infections ?

Answer 43

•Overuse of antibiotics **increases selection pressure** for resistant strains of bacteria Antibiotic resistant infections are **more difficult** to treat.

Question 44

What do mature B lymphocytes do ?

Answer 44

Produce specific antibodies (proteins) to neutralise a specific antigen.

Question 45

What is clonal selection of T/B lymphocytes ?

Answer 45

It is when the complementary antigen (from pathogen) and the receptor on the T/B cell's surface bind

Question 46

What causes clonal expansion ?

Answer 46

When a T cell becomes activated (whether by contact with antigen or interleukins) it undergoes mitosis rapidly in order to make more useful cells to destroy the pathogen The process of rapid division is clonal expansion.