Summary
Summary 4.1.1 Communicable diseases - OCR A-level biology
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This covers module 4 communicable diseases and immunity, this is a first year topic for ocr a level biology
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Communicable disease in plantsThere are u types of communicable disease Bacteria fungi virusandprotoctista
Bacteria is slightly smaller than eukaryotic cells theycauseharmthrough rapidmultiplication
and release of toxins
fungi this can grow informs of myceliumunderneath or hyphae on thesurface as
spores etc
theyfeedoff of dead organic materials andreleasesubstances to
breakdown skin and cellulose
virus viruses work through disrupting or altering geneticmaterialof cells
and then causemanufacture copies
protocistprotists operate through a host and feed on theircontents astheygrow
Plant Pathogens
Ring rot this causes rotting of tissue within the plant
bacteria
ack Sigatoka causes black spotting on the leave's reducing yield of plant
ungal
blight this can affect potato and tomatoes tubers and leaves
Orotoctista
baccomosaic a disease causing darkening of leaves this disrupts their ability
virus to photosynthesise sufficiently
direct plant transmission
disease can be directly transmissed through physicalandairbornemeans
fungal spores can be released into the air andpassed betweenplants
Pathogens can also spread when plantscome into physicalcontact with
contaminated soil
Indirect plant transmission
This can occur through a vector such as an insect carryingcontaigious
e.g dutch elm disease
pathogens transmissed via beetles
, Plant defences
passive defences
This is the plant defence that is alreadyfound within theorganism to prevent
entry of pathogens they can be physical or chemical
Physical
cellulose this is an insoluble wall forming an impermeable barrier
against pathogens
waxycuticle this prevents collection of water on the surface of plants which
survive
Pathogens
rely on to
callose this is deposited into sieve tube cells to block flowii of sap and
Preventspread of pathogens
tylose this a swelling of the walls of the xylem to blockflow of water
cells can close to block
entry
active defences
These respond to pathogens once infectedin the plant
Alkaloids these have a bitter taste preventing
herbivory
Terpenoids tanning phenols antifungalandantibacterialproperties
Hydrolytic enzymes can break down cells
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