4.1.1 Communicable Diseases

Question 1

Bacteria (pathogen)

Answer 1

Prokaryotes 
Shapes:
• bacilli (rod)
• cocci (sphere)
• vibrios (comma shape)
• spirilla (spiral)
• spirochaetes (corkscrew shape)

Cell walls:
• Gram positive bacteria (purple/blue stain)
• Gram negative bacteria (red stain)

Question 2

Viruses

Answer 2

Non-living

Invade living cells, host cell

Question 3

Protoctista (Protista)

Answer 3

Eukaryotic
Wide variety of feeding methods
Use animals as host
May need a vector

Question 4

Fungi

Answer 4

Eukaryotic
Multicellular
Digest food exracellularly before absorbing nutrients
Saprophytes - feed on dead/decaying matter
Produce spores which can spread

Question 5

Pathogens; damaging host directly

Answer 5

• viruses take over cell metabolism

* fungi digest living cells and destroy them

Question 6

Pathogens; producing toxins to damage host tissues

Answer 6

• most bacteria, toxins may break down cell membranes

* some fungi

Question 7

Plant diseases; ring rot

Answer 7

Bacterial

No cure

Question 8

Plant diseases; tobacco mosaic virus

Answer 8

Virus

No cure but resistant crop strains are available

Question 9

Plant diseases; potato blight

Answer 9

Fungus
Host cells
No cure but resistant strains, management and chemicals used to reduce risk

Question 10

Plant diseases; black Sigatoka

Answer 10

Fungus
No cure
Resistant strains being developed
Fungicides

Question 11

Animal diseases; tuberculosis

Answer 11

Bacterial
Destroys lung tissue
Suppresses immune system

Question 12

Animal diseases; bacterial meningitis

Answer 12

Bacterial
Infection of meninges of brain
Antibiotics will cure is early
Vaccines

Question 13

Animal diseases; HIV/AIDS

Answer 13

Virus

Destroys immune system

Question 14

Animal diseases; influenza

Answer 14

Viral
Kills ciliated epithelial cells
Flu vaccine
No cure

Question 15

Animal diseases; malaria

Answer 15

Protoctista 
Mosquitos 
No vaccine 
Limited cures 
Control vectors

Question 16

Animal diseases; ring worm

Answer 16

Fungal

Antifungal creams

Question 17

Animal diseases; athlete’s foot

Answer 17

Fungal

Antifungal creams

Question 18

Direct transmission in animals

Answer 18

• direct contact
• inoculation (break in skin)
• ingestion

Question 19

Indirect transmission in animals

Answer 19

• fomites (bedding,socks)
• droplet infection / inhalation
• vectors

Question 20

Factors affecting transmission of communicable diseases in animals

Answer 20

• overcrowding
• poor nutrition
• HIV
• climate change
• culture and infrastructure
• socioeconomic factors

Question 21

Direct transmission in plants

Answer 21

Contact of healthy plant w diseases plant

Question 22

Indirect transmission in plants

Answer 22

• soil contamination

* vectors (wind,water,animals)

Question 23

Factors affecting the transmission of communicable diseases in plants

Answer 23

• over crowding
• poor mineral nutrition
• damp, warm
• climate change

Question 24

Plant defended against pathogens; recognising an attack

Answer 24

Receptors respond to molecules

Defensive chemicals give alarm to other cells before they’re attacked

Question 25

Plant defended against pathogens; physical defences

Answer 25

Produce high levels of callose - act as barrier to pathogens entering

Question 26

Plant defended against pathogens; chemical defences

Answer 26

• insect repellant
• insecticides
• antibiotics
• antifungal compounds

Question 27

Animals; non-specific defences — Keelung pathogens out

Answer 27

• skin
• mucous membranes
• lysozymes in tears and urine

Blood clotting and repair
• thromboplastin
• serotonin

Inflammatory response
• mast cells activated, release histamines and cytokines
• histamines make blood vessels dilate, more leaky
• cytokines attract white blood cells

Question 28

Animals; non-specific defences — Getting rid of pathogens

Answer 28

• fevers - high temp inhibits pathogen production

* phagocytosis - wbc engulf and destroy pathogens (neutrophils/macrophages)

Question 29

The stages of phagocytosis

Answer 29

1) pathogens produce chemicals that attract phagocytes
2) recognise non-human proteins
3) phagocyte engulfs pathogen, eclipsed in vacuole called phagosome
4) phagosome combines w lysosomes forming a phagolysosome
5) enzymes from lysosome digest and destroy pathogen

Question 30

Helpful chemicals

Answer 30

Cytokines - cell signalling molecules, can stimulate specific immune system

Opsonins - ‘tag’ pathogens so their easily recognised

Question 31

Animals; specific immune system — antibodies

Answer 31

Y shape = immunoglobulins

Form antigen-antibody complex

Hinge region provides flexibility to bind to two separate antigens

Question 32

How antibodies defend the body

Answer 32

1) acts as oosonin, easily engulfed and digested
2) can’t invade once attached to antibody
3) a.b act as agglutinins cause complex’s to clump together - prevent spread, easily engulf
4) act as anti-toxins by binding to toxins

Question 33

Animals; specific immune system — Lymphocytes and the immune response

Answer 33

B lymphocytes - Bone marrow
T lymphocytes - Thymus gland
•T helper - bind to surface antigens, produce interleukins that stimulate activity of B cells
•T killer - produce perforin to destroy pathogen by making holes in cell membrane
•T memory - part of immunological memory
•T regulator - suppress immune system to control and regulate it
•B Plasma cells - produce antibodies
•B effector cells - divide to form the plasma cell clones
•B memory cells - immunological memory, remember specific antigen

Question 34

Animals; specific immune system — Cell mediated immunity

Answer 34

T lymphocytes respond to cells that have been changed in some way

1) phagocytosis
2) receptors of some T helper fit the antigens. These become activated and produce interleukins which stimulates more T cells to divide
3) clones T cells may develop into memory, produce interleukins, or stimulate development of clone T killer cells
4) cloned plasma cells produce a.b to bind to pathogen = primary immune response