4.1.1 - Communicable Disease (set B - Defence Against Pathogens) Flashcards
Outline how plants are able to recognise an attack?
- receptors in the cell respond to molecules from pathogens or chemicals produced when cell wall is attacked
- stimulates release of signalling molecules that switch on genes in the nucleus
- triggers cellular responses - eg producing defensive chemicals/ sending alarm signals to unaffected cells to trigger defences or physically strengthens cell walls
Outline plants physical defences against pathogens - focus on callose?
produce high levels of callose (polysaccharide) when attacked - which is deposited between cell walls and membrane
callose acts as barrier preventing pathogen entering cells around infection site - lignin is added to further strengthen and thicken barrier
- callose blocks sieve plates in phloem - sealing of infected part, preventing spread (also deposited in plasmodesmata to stop spread)
Outline plants chemical defences against pathogens - give 4 and provide examples?
- insect repellents - eg pine resin
- insecticides - eg caffeine which is toxic to insects and fungi
- antibacterial compounds - eg phenols - which are antiseptics made in plants disrupt pathogen cell membranes
- general toxins - plants can make compounds that can be broken down to from cyanide compounds - toxic to living organisms
What are the two lines of defence mammals have against invasion by pathogens?
- the primary non-specific defense
- specific immune response (slower than non specific - up to 14 days but faster second invasion)
Outline the non-specific defences which keeps pathogens out?
- the skin
- mucous membranes
- lysozymes in tears and urine + acid in the stomach
Expulsive reflexes - eg coughing/sneezing/vomiting/diarrhoea - expels mucus containing pathogen or contents of the gut containing pathogens
Explain how the skin acts as a barrier preventing pathogens entering?
- skin covers the body, preventing entry of pathogens - has a flora of healthy microorganisms that outcompete pathogens for space on the body surface
- skin produces oily substance, sebum - which Inhibts pathogen growth
Explain how mucous membranes help keep pathogens out?
- airways of gas exchange systems are lined by mucous membranes which secrete sticky mucus (containing lysozymes and phagocytes) - trap microorganisms destroying bacterial and fungal cell walls
Explain how blood clotting and wound repair help prevent pathogens entering the body?
- when the skin is cut and breached - pathogens can enter the body
- when platelets come into contact with collagen in skin they adhere and secrete thromboplastin and serotonin
- clot dries out forming tough scab - starting process of wound repair
Explain how the substance thromboplastin is involved in wound repair?
- enzyme which triggers a cascade of reactions resulting in the formation of a blood clot
Explain how the substance seretonin is involved in wound repair?
- causes smooth muscle in the walls of the blood vessel to contract - so they narrow which reduces the supply of blood to the area
Explain how wound repair occurs?
- formation of scab - aided by secretion of thromboplastin and serotonin
- epidermal cells below scab start to grow - sealing wound permanently, damaged blood vessels regrow
- collagen fibres deposited to provide tissue strength
- scab sloughs off when the wound is healed
Outline the inflammatory response to pathogens?
- localised response - results in inflammation at the site of a wound
- mast cells are activated in damaged tissue - they release chemicals (histamines and cytokines)
Outline the chemicals involved in inflammatory response - histamines and cytokines?
Histamines - make blood vessels dilate - causing localised heat and redness - prevents pathogens reproducing
Histamines - make blood vessel walls more leaky so blood plasma is forced out - tissue fluid causes swelling and pain
Cytokines - attract phagocytes to site - which dispose of pathogens
Outline the non-specific defences which gets rid of pathogens?
- fevers
- phagocytosis
Explain how fevers help get rid of pathogens?
- cytokines stimulate hypothalamus causing temperature to increase
Pathogens reproduce best at or below 37 degrees - higher temps Inhibits pathogen reproduction
Specific immune system works faster at higher temperatures
Explain how phagocytosis can help get rid of pathogens?
- phagocytes are specialised WBC’s that engulf and destroy pathogens - two main types - neutrophils and macrophages
- build up at the site of an infection and attack pathogens
takes 10 minutes for neutrophil to engulf and destroy pathogen - macrophages take longer
Outline the stages of phagocytosis - and its involvement in getting rid of pathogens?
1) pathogens produce chemicals that attract phagocytes
2) phagocytes recognise non-human proteins (antigens) on pathogen as non-self and binds to it
3) phagocyte engulfs pathogen and encloses it in a vacuole called a phagosome
4) phagosome combines with a lysosome forming a phagolysosome
5) enzymes from lysosome digest and destroy the pathogen
6) digested pathogen absorbed by phagocyte-antigens combine with MHC in cytoplasm
7) MHC antigen complex displayed on phagocyte membrane - making an antigen presenting cell
stages 6 and 7 for macrophages
Explain how the stages of phagocytosis varies between neutrophils and macrophages?
- takes neutrophil 10 mins to engulf and destroy pathogen
- macrophages undergo a more complex process (stages 6 and 7) - macrophages combines glycoprotein (MHC) with antigens from digested pathogen - which moves to surface membrane becoming an antigen-presenting cell (APC) which stimulate other cells in specific immune system response
Explain the role of cytokines produced by phagocytes?
- act as cell-signalling molecules - informing other phagocytes that the body is under attack - stimulates them to move to the site of infection
- can also increase body temp, stimulating specific immune system
Explain the role of opsonins produced by phagocytes?
- chemicals that bind to pathogens - and ‘tag’ them - can be more easily recognised by phagocytes
- phagocytes have receptors on cell membranes that bind to opsonins
Outline the structure of antibodies?
- Y-shaped glycoproteins called immunoglobulins - bind to specific antigen on pathogen or toxin
- made up of 2 identical long polypeptide chains (heavy chains) and two much shorter identical chains (light chains) held together by disulphide bridges also disulphide bridges in polypeptide chains
- also have a hinge region - providing flexibility and allowing for binding to 2 separate antigens
- variable region different on different antibodies
Explain the role of the hinge region?
Provides the molecule with flexibility - allowing it to bind two separate antigens - one at each of its antigen-binding sites
Explain how antibodies bind to antigens?
- based on ‘lock and key’ mechanism - binding site on light and heavy chain known as variable region (makes antibody specific)
- rest of antibody same - constant region
Antibody blinds to antigen forming antigen-antibody complex - hinge region allows it to bind two separate antigens at each binding site
Outline how antibodies defend the body?
1) antibody of antigen-antibody complex acts as an opsonin (complex is easily engulfed by pathogen)
2) pathogens can no longer effectively invade host cells once they are part of an antigen-antibody complex
3) antibodies act as agglutinins causing pathogens carrying antigen-antibody to clump together - preventing spread
4) antibodies act as anti-toxins - binding to toxins produced by pathogens - making them harmless
