Defence against pathogens Flashcards
How do plants recognise an attack?
Receptors respond to pathogen when cell wall attacked
–> stimulates release of signalling molecules to switch on genes in nucleus.
–> produces defensive chemicals, send alarms to unaffected cells –> trigger defence + physically strengthening cell walls.
What fetaures does a plant help to defend against pathogens?
Waxy cuticle
Closing stomata
Thick cellulose cell walls
What are the plants physical denfence?
Produce high levels of callose (b-1,3 + b-1,6)
Synthesised + depositied between cell walls + cell membrane of cells next to infected cells.
Act as barriers + prevent pathogens entering plant cell around site of infection.
Lignin added –> make mechanical barrier to invasion thicker + stronger.
–> blocks sieve plates in phloem –> seals off infected parts + prevents spread of pathogen
Depositied in plasmodesmata: prevent pathogen from spreading.
What are the chemical defences for plants?
Insect repellants: pine resin + citronella
Insecticides: pyrethrins: acts as neurotoxins
Antibacterial compounds (antibiotics): disrupt bacterial + fungal cell membranes
Antifungal compounds: phenols (chitinases break down chitin in fungal cell walls)
Anti-oomycetes
General toxins
What is the primary non-specific defences against pathogens?
Defence against all pathogens
Always present + activated very rapidly
What prevents the entry of pathogens?
Muscous membranes: traps pathogens
Expulsive reflexes: cough/sneeze
Skin -> oily sebum: inhibits growth of pathogen
How does blood clotting prevent the entry of pathogens?
Platetes come to contact with collagen in skin –> adhere + secrete thromboplastin (triggers cascade of reactions) + serotonin (make smooth muscle in BP contract)
Epidermal cells below scab grow + seal wound forever.
What is the inflammatory response?
Localised to site of wound.
Mast cells activated –> release histomines + cytokines.
What do histamines + cytokines do?
Histamines: make BP dialte -> localised heat + redness
Make BP walls more leaky -> blood plasma forced out (now tissue fluid)
Causes swelling + pain
Cytokines: attract WBC (phagocytes) to site–> phagocytosis
How do fevers get rid of pathogens?
Normal body temp 37 –> maintained by hypothalamus
Higher temp = inhibit pathogen reproduction
Specific immune system works faster at higher temp
State difference between neutrophil + macrophage:
Neutrophil: rapidly engulf + destroy pathogens infection site –> lobed nucleus
Macrophages - engulf + digest pathogens but also present the pathogen’s antigens on its cell surface to activate other cells in the immune system.
Describe stage of Phagocytosis (6 marks)
Macrophage recogbises antigen as foreign
Macrophage engulfs pathogen, forming phagosome
Lysosomes fuse with phagosomes –> form phagolysosome –> lysozymes digest pathogen within.
Macrophage digest everything apart from antigen.
Present pathogen’s antigen on surface to activate other cells = APC
What is the MHC?
Glycoprotein bind to antoigen + present them on macrophage cell surface membrane.
What are antigens?
Unique molecules (proteins) found on surface of cells.
Help immune system distinguish between self + non-self (foreign). Foreign cell
What do antigens allow immune system to detect?
Pathogens
Abnormal body cells
Toxins
cells from organisms of same species
