defences against pathogens Flashcards
1
Q
plant defenses acting as barriers
A
- waxy cuticle of leaves
- bark on trees
- cellulose cell walls
2
Q
what do plants do with diseased tissue
A
they seal it off and sacrifice it
3
Q
how do plants recognise an attack
A
- receptors in cell membrane
- molecules released from pathogens are detected
- when pathogenic enzymes break down cell wall, the products are recognised
- signalling molecules alert nucleus to attack
- polysaccharides (callose+lignin) strengthen cell walls
- defensive chemicals give the alarm to other cells before they are attacked
- defensive molecules directly attack pathogen
4
Q
production of callose
A
- deposited between cell walls and cell membrane in cells next to infected cells
- these act as barriers to prevent pathogens entering cells
- lignin is added, making barrier thicker and stronger
- callose blocks sieve plates in phloem- sealing off infected part and preventing spread of pathogens
- callose deposited in plasmodesmata between infected cells and neighbour cells
5
Q
plant defensive chemicals examples
A
- insect repellents
- insecticides
- antibacterial compounds
- antifungal compounds (chitinases- enzyme that breaks down chitin in fungal cell walls)
- anti-oomycetes (glucanases)
- general toxins (cyanide)
6
Q
animal non specific defences
A
- skin prevents entry of pathogens (produces sebum which inhibits growth of pathogens)
- mucous membranes secrete sticky mucus which traps microorganisms and contains lysozymes and phagocytes
- lysozymes in tears, urine and stomach acid
- expulsive reflexes (coughs, sneezes eject mucus, vomiting/diarrhoea expels contents of gut)
7
Q
blood clotting
A
- platelets contact with collagen in skin or wall of damaged blood vessel
- they adhere and secrete substances:
- thromboplastin enzyme that triggers reactions in formation of a blood clot
- serotonin makes smooth muscle in walls of blood vessels contract so they reduce blood supply to the area
- clot dries and forms scab which keeps pathogens out
- epidermal cells and damaged blood vessels regrow
- collagen fibres deposited to give new tissue strength
- scab falls off when new epidermis reaches normal thickness
8
Q
inflammatory response
A
- mast cells are activated in damaged tissue which release histamines and cytokines
- histamines make blood vessels dilate (heat and redness) and raised temp prevents pathogens reproducing
- histamines make blood vessel walls leaky so plasma is forced out and becomes tissue fluid which causes swelling (oedema) and pain
- cytokines attract WBCs
9
Q
fevers
A
- normal temp-37
- cytokines stimulate hypothalamus to reset thermostat so temp goes up when pathogen enters body
- high temps inhibit pathogen production
- specific immune system works faster at higher temps
10
Q
what are the 2 types of phagocytes
A
neutrophils
macrophages
11
Q
what does pus consist of
A
dead neutrophils and pathogens
12
Q
stages of phagocytosis
A
- pathogens produce chemicals that attract phagocytes
- phagocytes recognise non-self antigen
- phagocytes engulfs pathogen and encloses it in a vacuole called a phagosome
- phagosome combines with lysosome to form phagolysosome
- enzymes in lysosome digest and destroy pathogen
13
Q
antigen presenting cell
A
when a phagocyte presents the destroyed pathogen’s antigens to activate other immune system cells
14
Q
cytokines
A
- produced by phagocytes that have engulfed a pathogen
- act as cell-signalling molecules
- which inform other phagocytes that body is under attack and stimulates them to move to site of infection/inflammation
- cytokines increase body temp and stimulate specific immune system
15
Q
opsonins
A
- bind to pathogens so they can be more easily recognised by phagocytes
- phagocytes have receptors on membrane that bind to opsonins and the phagocyte engulfs the pathogen
16
Q
neutrophils
A
- multi-lobed nucleus
- can pass into tissue fluid as they can change shape
- short-lived
17
Q
macrophages
A
- longer and can engulf a greater number of pathogens
- C shaped nucleus
- travel in the blood as monocytes
- tend to settle in body organs (lymph nodes) where they develop into macrophages
