a disease that is spread from one host to another caused by pathogens
Vectors
An organism that transmits disease by conveying pathogens from one host to another
2 ways bacteria can be identified
by their basicshapes
by their cellwalls
What colour do gram-positive bacteria and gram-negative bacteria appear under staining respectively
purple blue (+) and red (-)
Viruses
smaller than bacteria and other pathogensinside the genetic material surrounded by a protein invade living cells in order to reproducewhen they invade, the cells are damaged or destroyed in the process of releasing new particles to infect other cells
Protoctista
unicellular and multicellular eukaryotic organisms
may be auto or heterotrophic
Fungi
Kingdom composed of heterotrophs; many obtain energy and nutrients from dead organic matter (saprophytes)some are parasitic
Bacteriophage
A virus that infects bacteria
How do viruses damage host tissues directly
virus attaches to host cell
insertion of viralnucleic acid
replication of viral nucleic acid
synthesis of viral protein
assembly of viral particles
lysis of host cell, spreading toxic particles to other cells
How can toxins damage host tissues
break down cell membranes
damage or inactivate enzymes
interfere with host cell genetic material
Example of a plant and animal disease (bacteria)
Ring rot and Tuberculosis or Bacterial meningitis
Example of a plant and animal disease (virus)
Tobacco mosaic virus and HIV/AIDS or Influenza
Example of a plant and animal disease (fungus)
Black sigatoka and Ring worm or Athletes foot
Example of a plant and animal disease (protoctist)
Potato blight and Malaria
Direct methods of transmission
directcontact - kissing, touching etc.
inoculation - animal bite, break in skin etc.
ingestion- contaminated food etc.
Indirect methods of transmission
fomites- inanimate objects such as socks
droplet infection- minute droplets of saliva etc.
vectors
Factors affecting transmission of communicable diseases in animals
overcrowded living and working conditions
poor nutrition
compromised immune system
poor disposal of waste
climate change
culture and infrastructure
socioeconomic factors
Types of vectors
wind
water
animals
humans
Factors affecting transmission of communicable diseases in plants
planting crops susceptible to disease
overcrowding
poor mineral nutrition
damp warm conditions
climate change
How do plants recognise an attack
plant cells recognise molecules produced by pathogens
when pathogen(ie enzymes) break down the plant cellwall, the breakdown products are recognised
signalling molecules alert nucleus to attack:
polysaccharides (callose and lignin) made to strengthen cell wall)
alarm other cells before they are attacked
attack pathogen directly
Function of callose
deposited between cell walls and membranes to prevent pathogen entry
block sieve plates in phloem sealing infected parts
deposited in plasmodesmata to prevent spread
Chemical defences of plants
insect repellents
insecticides
antibacterial compound
antifungal compound
anti-oomycetes
general toxins
Non-specific defences animals- skin
covers the body preventing the entry of pathogens
has skin flora that outcompete pathogens for space on body surface
skin also produces sebum which inhibits pathogen growth
Non-specific defences animals- mucous membranes
many of the body tracts are lined by this
secrete stickymucus trapping microorganisms and contains lysozymes and phagocytes
Non specific defences animals- lysozymes
found in tears, urine and the acid in the stomach
contains hydrolytic enzymes to break down pathogens
Blood clotting and wound repair
cut detected by plateletsthromboplastin is released
serotonin is released clot dries and scabs form epidermal cells below the scab grows sealing wound damaged blood vessels regrowing collagen fibres deposited to give strength scab falls off
Thromboplastin (blood clotting)
an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot
Serotonin (blood clotting)
makes the smooth muscle in the walls of the blood vessels contract, so they narrow and reduce the supply of blood to the area
Inflammatory response (non specific animal defence)
localised response to pathogens resulting in inflammation at the site of a wound activating mast cells releasing histamines and cytokines
Mast cells
Cells that release chemicals (such as histamine or cytokines) that promote inflammation.
Histamine role (in inflammation)
make blood vessels dilate causing localised heat and redness
temperature raised to prevent pathogensreproducing
make blood vessel walls leaky so blood plasma is forced out as tissuefluid causing swelling and pain
Cytokines (in inflammation)
attract white blood cells (phagocytes) to the site
they dispose of pathogens by phagocytosis
Fever (non specific response)
when pathogen invades body
cytokines stimulate hypothalamus to increase temperature
higher temperatures inhibit pathogen reproduction
specific immune system works faster at higher temperatures
Why is increasing body temperature good for fighting off pathogens
higher temperatures inhibit pathogen reproduction
specific immune system works faster at higher temperatures
2 types of phagocytes
neutrophils and macrophages
Phagocytosis stages (neutrophil)
Pathogens produce chemical that attractsphagocytes and recognise it as non-self by then binding to it
Phagocyte engulfspathogen to form phagosome
Phagosome binds with lysosome to form phagolysosome
Lysosome enzymesdigest and destroy the pathogen
Phagocytosis stages (macrophage)
After lysosome digests the pathogen, it combines antigens from the pathogen surface membrane with the major histocompatibility complex (MHC)
The MHC complex moves pathogen antigens to the macrophage's surface membrane to become an antigen-presentingcell (APC)
Antigen-presenting cells (APCs)
cells such as B cells, macrophages, and dendritic cells that can present exogenous antigens to naive or memory T cells, activating them
Cytokines
act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation
Opsonins
chemicals that bind to pathogens and tag them so they are recognised more easily by phagocytes, e.g. antibodies.