Biodiversity, Evolution And Disease

Question 1

What is a pathogen? And what are some examples?

Answer 1

A microorganism that causes a disease
- virus
- fungi
- protist
- bacteria

Question 2

What are some characteristics of bacteria? And how do they cause disease?

Answer 2

• prokaryotic organism
• small single- celled organism that reproduce rapidly
  They cause disease by:
  - damaging cells
  - releasing toxic waste products/substances

Question 3

What are some characteristics of fungi?

Answer 3

• eukaryotic organism
• commonly grows under the skin surface in animals forming a mycelium
  - a mycelium is a network of fungal threads (hyphae)
  - hyphae can cause redness and irritation when they grow through the
  Skin to release spores - asexual reproduction

Question 4

What are some characteristics of viruses? How do they infect?

Answer 4

• not alive
• small particles which contain genetic material (DNA or RNA)
• invade and take over cells so they produce more copies of the virus
• cell then dies and releases new virus particles which then infect healthy cells

Question 5

What are protist? How do they cause disease? Examples?

Answer 5

• eukaryotic organisms
• mostly unicellular
  Can cause disease by entering host cells and feeding on contents as they grow
• malaria parasites

Question 6

What is direct transmission? What are some examples?

Answer 6

When a pathogen is transmitted directly from one organism to another
- direct physical contact
- faeco - oral transmission
- droplet infection
- spores

Question 7

What is indirect transmission?

Answer 7

When a pathogen is transmitted indirectly from one host to another via a vector (another organism pathogens use for entry)

Question 8

What are some examples of bacteria?

Answer 8

Tuberculosis, bacterial meningitis and ring rot

Question 9

What are some examples of a virus?

Answer 9

HIV/AIDS, influenza, tobacco mosaic virus

Question 10

What are some examples of a fungus?

Answer 10

Black Sigatoka, ringworm and athletes foot

Question 11

What are some examples of a protist?

Answer 11

Blight and malaria

Question 12

What’s the host of tuberculosis? And how is it transmitted?

Answer 12

Humans & cattle
- droplet infection

Question 13

What is the host of bacterial meningitis? How is it transmitted?

Answer 13

Humans (mostly young)
- through droplet infection

Question 14

What’s the host of ring rot? How is it transmitted?

Answer 14

Potatoes
- direct physical contact
- through infected seeds

Question 15

What’s the host of HIV/AIDS? How is it transmitted?

Answer 15

Humans
- through direct physical contact

Question 16

What is the host of influenza? How is it transmitted?

Answer 16

Humans
- by droplet infection

Question 17

What is the host of tobacco mosaic virus? How is it transmitted?

Answer 17

Plants
- through direct physical contact

Question 18

What’s the host of black Sigatoka? How

Question 19

What’s a physical defence in plant defences?

Answer 19

Something that prevents the spread of the pathogen

Question 20

What’s a chemical defence in plant defences?

Answer 20

A substance that damages the pathogen directly

Question 21

What’s a passive defence?

Answer 21

Defences that are present before infection

Question 22

What’s active defence?

Answer 22

Changes to defences in response to a pathogen infection

Question 23

How does callose prevent the spread of pathogens? And what type of defence?

Answer 23

A physical passive defence
- large polysaccharide
• its deposited at the end of sieve plates (phloem)
• blocks the spread of pathogens through the phloem
• also blocks plasmodesmata
- channels between cells

Question 24

What is Tylose and how does it stop the spread of pathogens?

Answer 24

It’s a physical passive defence
- a balloon- like swelling/projection that fills the xylem vessel and eventually blocks it
- contains high concentration of anti-microbial chemicals

Question 25

What are some active defences that happen when a pathogen is detected?

Answer 25

- cell walls can become thicker – additional cellulose can be deposited near the pathogen and prevent cellular penetration - necrosis can take place – deliberate cell suicide – limiting pathogen access to water and nutrients

Question 26

What is necrosis?

Answer 26

Deliberate cell suicide

Question 27

What’s are primary defences in animals?

Answer 27

Non-specific defences that prevent pathogens from entering the body

Question 28

What does it mean when the defence is non-specific?

Answer 28

That the defences are always the same, regardless of the type of pathogen trying to enter the body.

Question 29

What type of defence is the skin and what is skin?

Answer 29

Primary defence -outer layer of dead, hardened cells filled with keratin that acts as a physical barrier to pathogens - keratin is a tough fibrous protein - skin cells also secrete sebum – an oily substance which contains fatty acids which can prevent the growth of bacteria (acidic conditions)

Question 30

What defence is blood clotting and how does it prevent spread of pathogens?

Answer 30

Primary defence - blot clot blocks the cut and dries it (forming a scab) - as the clot dries it pulls the cells on either side of the clot together - closing it - under this scab, new skin cells are made to replace it (from the epidermal stem cells)

Question 31

What does an enzyme cascade consist of

Answer 31

A series of enzymes in which the product of one enzyme is the substrate for the rest

Question 32

What is inflammation?

Answer 32

Swelling and redness of tissue caused by infection

Question 33

What is a mucous membrane?

Answer 33

Specialised epithelial tissue that is covered by mucus

Question 34

What is histamine? What effects does it have on tissues?

Answer 34

A cell signalling substance released by mast cells when microorganism are detectied in the tissue (during inflammation) - it causes vasodilation, which is widening of blood vessels, which results in swelling and temperature increase - increases the permeability of blood vessel walls which allows fluid to leave the blood

Question 35

What do cytokines do during inflammation?

Answer 35

- attract phagocytes to the area of infection - increase body temperature

Question 36

What are mast cells?

Answer 36

Specialised cells that detect pathogens and then release histamine to initiate inflammation

Question 37

What are the steps in inflammation?

Answer 37

1. Mass cells in the tissue detect the pathogens and release a cell-signalling chemical called histamine 2. Histamine causes vasodilation which widens blood vessels and makes the walls of capillaries in tissues more permeable 3. White blood cells (phagocytes) circulating in the bloodstream can leave the bloodstream through the wall of the capillaries and reach the site of infection in the tissue 4. White blood cells attack pathogens at the site of infection in the tissue 5. Plasma also leaves the bloodstream, which results in an increase in tissue fluid. This causes swelling (oedema) 6. Excess tissue fluid is drained into the lymphatic systems 7. Other immune cells (lymphocytes) are stored in the lymphatic system come into contact with pathogens in drained tissue fluid and activate a specific immune response.

Question 38

What is phagocytosis?

Answer 38

The engulfment of pathogens and is carried out by neutrophils (type of white blood cells)

Question 39

What are the 3 steps involved in phagocytosis?

Answer 39

1. Recognition of the antigens on the surface of a pathogen 2. Phagocyte engulfs the pathogen and forms a phagosome 3. A lysosome fuses with the phagosome

Question 40

What is clonal selection?

Answer 40

The process by which T cells and B cells become activated when their cell surface receptors/antibodies bind to a matching antigen.

Question 41

What is clonal expansion?

Answer 41

Happens after clonal selection It’s when the activated T cells and B cells increase in number through cell division and begin to differentiate into specialised cells.

Question 42

What are the two main types of white blood cells?

Answer 42

-phagocytes -lymphocytes