Communicable Diseases, Disease Prevention And The Immune System

Question 1

Name 4 groups of pathogen that can cause communicable diseases

Answer 1

Bacteria, Fungi, Protocista, Viruses

Question 2

Describe 2 fungal infections

Answer 2

Cattle Ringworm - Direct Contact with infected cattle
Athletes Foot - Direct Contact with fomites touched by infected individuals

Question 3

How are communicable pathogens transmitted directly ?

Answer 3

Droplet transmission -Breathing in infected droplets (coughing, sneezing, talking, spitting of an infectious person.)
Sexual transmission - Having unprotected sexual intercourse with an infectious person (exchange of bodily fluids)

Question 4

How are communicable pathogens transmitted indirectly ?

Answer 4

Water and food - Infectious person sheds the pathogen into a water/food, which is then consumed by another person
Spores - Products of asexual reproduction, produced by organisms such as fungi, and some protoctist species. Have the ability to cause disease when they gain entry into hosts
Vectors - Organisms which are first infected with the pathogen before passing the disease onto the final host. E.g. in malaria, infected mosquitoes act as vectors by spreading the causative protoctist to humans

Question 5

How do living conditions affect disease transmission ?

Answer 5

Overcrowding increases direct transmission
Climate determines which organisms can survive e.g. malaria is more prevalent in tropical countries, where mosquito (vector) can breed
Social factors influence how quickly people are treated, which can increase/decrease direct transmission

Question 6

Name 4 physical barriers to pathogen entry in plants

Answer 6

Cellulose cell walls
Lignified layer
Waxy upper cuticle
Old vascular tissue is blocked to prevent pathogens from spreading inside the plant

Question 7

Describe 2 mechanical responses to infection in plants

Answer 7

Guard cells close stomata
The thick polysaccharide callose is produced & deposited between the cell wall & plasma membrane to increase entry distance/limit spread

Question 8

What is necrosis ?

Answer 8

Injury activates intracellular enzymes in plants that kill cells near the site of infection to prevent pathogen from spreading

Question 9

Describe the chemical defences plants use against pathogens

Answer 9

Terpenoids (essential oils) e.g. menthols act as antibacterials.
Phenols e.g. tannin inhibit insects from attacking by interfering with digestions
Alkaloids e.g. caffeine & morphine deter herbivores from feeding because they taste better
Defensins Inhibit transport channels
Hydrolytic enzymes e.g. chitinases break down cell wall of invading organisms

Question 10

Name 5 barriers to infection in animals

Answer 10

Skin is tough keratin layer
Blood clotting prevents pathogens from entering through skin lesions
Hydrochloric acid kills bacteria
Harmless bacteria in gut & on skin surface increase interspecific competition with pathogens
Mucous membranes trap pathogens and may secrete anti microbial enzymes

Question 11

What are expulsive reflexes ?

Answer 11

Body attempts to force foreign substances out:
- Irritation of mucous membranes in nostrils causes sneezing
Irritation of ciliates epithelium in respiratory tract causes coughing

Question 12

Name 4 ways the nonspecific immune systems responds to infection

Answer 12

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

Question 13

Outline the process of inflammation

Answer 13

Damaged vessels release histamines
, causing vasodilation
Blood flow & permeability of blood vessels increase
White blood cells & plasma move into the infected tissues

Question 14

How does blood clotting occur ?

Answer 14

Blood platelets form plug & release chemicals that enhance clotting
Prothrombin changes into thrombin, its active form
Fibrinogen changes into insoluble fibrin which covers wound

Question 15

Name the 2 types of white blood cells involved in phagocytosis

Answer 15

Neutrophils
Macrophages (can become APCs)

Question 16

How does phagocytosis destroy pathogens ?

Answer 16

Phagocyte moves towards pathogen which may have been marked by opsonise via chemotaxis
Phagocyte engulfs pathogen via endocytosis to form a phagosome
Phagosome fuses with lysosomes (phagolysome)
Lysozymes digest pathogen
Phagocyte absorbs the products from pathogen hydrolysis

Question 17

Explain the role of antigen-presenting cells (APCs)

Answer 17

Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)
Enhances recognition by T(helper) cells, which cannot directly interface with pathogens/antigens in bodily fluid
Secrete cytokines that are involved in stimulating specific immune response

Question 18

What are lysozymes ?

Answer 18

Digestive enzymes. Found in lysosomes as well as many secretions e.g. tears & mucus. Damage bacterial cell walls, causing osmotic lysis

Question 19

Outline how to prepare blood to be observed under a microscope

Answer 19

Smear a drop of blood onto a slide using a spreader held at 45*
Add leishman stain then a buffer rinse

Question 20

Name the 2 types of specific immune response

Answer 20

Cell-mediated
Humoral

Question 21

Outline the process of cell-mediated response

Answer 21

Complementary T(Helper) lymphocytes bind to foreign antigen on APC
Cell signalling via secretion of interleukins stimulates:
- a clonal expansion of complementary T(Helper) cells (Rapid mitosis): become memory cells or trigger humoral response
- clonal expansion of cytotoxic T cells: secrete enzyme perforin to destroy infected cells

Question 22

Outline the process of the humoral response

Answer 22

Complementary T(Helper) lymphocytes bind to foreign antigen on antigen-presenting T Cells
Release cytokines that stimulate clonal expansion (Rapid mitosis) of complementary B lymphocytes
B Cells differentiate into plasma cells
Plasma cells secrete antibodies with complementary variable region to antigen

Question 23

Describe the structure and function of B and T lymphocytes

Answer 23

Many specific receptors & immunoglobulins on surface
B cells differentiate into plasma cells to secrete antibodies
3 Types of T Cell: T helper (secrete cytokines), T killer (secrete perforin), T regulator (Supress other immune cells to prevent autoimmune disease)

Question 24

What is antibody? Describe its structure

Answer 24

Proteins secreted by plasma cells
Quaternary structure: 2 ‘Light chains’ held by disulphide bridges, 2 longer ‘heavy chains’
Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen
The rest of the molecule is known as a the constant region
Refer To GoodNotes

Question 25

How do antibodies lead to the destruction of a pathogen ?

Answer 25

Agglutinins form antigen-antibody complexes to enhance phagocytosis
Activation of complement
Opsonises mark microbes for phagocytes
Antitoxins are toxins insoluble via precipitation/ neutralisation

Question 26

What are memory cells ?

Answer 26

Specialised T(Helper)/B cells produced from primary immune response
Remain in low levels in the blood
Can divide very rapidly by mitosis if organism encounters the same pathogen again

Question 27

Contrast the primary and secondary immune response

Answer 27

Secondary;
- Faster rate of antibody production
- Shorter time lag between exposure & antibody production.
- Higher concentration of antibodies
- Antibody level remains higher after the secondary response
- Pathogen usually destroyed before any symptoms

Question 28

Compare and contrast passive and active immunity

Answer 28

Both involve antibodies & can be natural or artificial
Passive: no memory cells & antibodies not replaced when broken down = short-term
Immediate
Antibodies from external source
No direct contact with antigen necessary
Active: Memory cells produces = long-term
Time lag
Lymphocytes produce antibodies
Needs direct contact with antigen

Question 29

Give examples of passive and active immunity

Answer 29

Passive natural: antibodies in breast milk/across placenta
Passive artificial: anti-venom, needle stick injections
Active natural: humoral response to infection
Active artificial: vaccination

Question 30

Define ‘Autoimmune disease’ and give examples

Answer 30

Immune system produces antibodies against its own tissues
Rheumatoid arthritis: immune system targets synovium lined joints, causing inflammation
Lupus: Results in inflammation throughout body

Question 31

Explain the principles of vaccination

Answer 31

Vaccine contains dead/inactive form of a pathogen or antigen
Triggers the primary immune system
Memory cells are produced and remain in the bloodstream, so secondary response is rapid & produces a higher concentration of antibodies
Pathogen is destroyed before it causes symptoms

Question 32

Define endemic and epidemic

Answer 32

Endemic: disease occurs routinely in a geographical area
Epidemic: temporary rapid increase in incidence of disease in a geographical area

Question 33

What role do vaccines play in preventing epidemics ?

Answer 33

Routine vaccinations of 80%-90% of population reduces available carriers of pathogen, resulting in herd immunity. Limited by country’s resources

Vaccinating close contacts of infected individual limits spread of pathogen, but raises issues of distributive justice

Programs have changed to account for informed consent & maximum beneficence even during epidemic

Question 34

What are the benefits of using antibiotics to treat bacterial infection ?

Answer 34

Effectively reduce population of bacterial colony. Used widely since discovery of penicillin in mid-20th century

Question 35

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

Answer 35

Overuse of antibiotics increases selection pressure for resistant strains of bacteria. Antibiotic-resistant infections e.g. caused by MRSA & Clostrdium difficult Are difficult to teat