Communicable diseases

• Gram positive bacteria looks purple/ blue under a light microscope. ( stain with crystal violet) an example of this is MRSA
• Gram negative bacteria looks red under a light microscope ( stain with safranin) an example of this is E.coli
• The 4 types of bacteria shapes are: Coccus, Bacillus, Spirillum, and vibrio
• The cell wall affects how bacteria respond to antibodies
• Bacteria reproduce by binary fission
• The problems with bacteria reproducing so quickly is: food starts to spoil more quickly, antibiotic resistance, can produce a lot of toxins and takes longer to full recover.
• Bacteria cause disease by antigen on bacterium, produce toxins and cause symptoms by cell damage
• One bacterium can divide into two new bacteria every 20 minutes. How many would you have after 4 hours

  4096
• Tuberculosis (TB) is cause by bacteria. It damages the lung tissue and supresses the immune system so the body is less likely to fight other diseases. It can be cured with antibiotics
• Bacterial meningitis is caused by a bacteria. It affects humans and destroys the meninges of the brain which can spread to other parts of the body and cause blood poising or death
• Ring rot is caused by bacteria. It affects potatoes and tomatoes. It can destroy up to 80% of the crop and there is no cure. Once infected, a field cannot grown potatoes for 2 years
• Define the terms "communicable disease" and "pathogen"

  Communicable disease - diseases that can be passed from one organism to another of the same or of different species

  Pathogen - microorganism that causes disease
• State the 4 different types of pathogen

  Bacteria

  Virus

  Fungi

  Protoctists
• Draw, label and annotate a diagram of a generalised virus

  Genetic material with a protein coat

  May have enzymes, membrane (stolen from host cell)

  
• Draw and label a series of diagrams to describe the general reproductive cycle of a virus

  Virus binding to surface of cell - receptor on surface on virus and surface protein on host cell bind

  Inject genetic material

  Copy genetic material (using host's metabolism)

  Protein synthesis to make capsid (uses ribosomes of host cell)

  New viruses constructed

  New viruses exit the cell - bursts (or budding)

  
• Describe 5 general ways in which pathogens can damage host tissue, thereby causing harm

  Produce toxins, Inhibit enzymes, burst cells, digest cells, inhibit nervous system
• Identify the host species of, and the type of pathogen causing, the following plant diseases: ring rot, tobacco mosaic virus, potato blight, black sigatoka

  Ring rot - Bacteria - Potatoes, tomatoes, aubergines

  Tobacco mosaic virus - Virus - tobacco plants, tomatoes, peppers, cucumbers

  Potato blight - Protoctist - potatoes, tomatoes

  Black sigatoka - Fungus - Bananas
• Identify the host species of, and the type of pathogen causing, the following animal diseases: tuberculosis, bacterial meningitis, AIDS, Influenza, Malaria, Ring worm, Athlete's foot


  Tuberculosis - Bacteria - Humans, cows, pigs, badgers, deer

  Bacterial meningitis - Bacteria - Humans

  AIDS - Virus - Humans, non-human primates

  Influenza - Virus - Humans, birds, pigs

  Malaria - Protoctist - Humans

  Ring worm - Fungus - Cattle, dogs, cats, humans

  Athlete's foot - Fungus - Humans
• Define the terms "vector", "spore", and "contagious disease"

  Vector - a living or non-living factor that transmits a pathogen from one organism to another

  Spore - a minute, typically one-celled, reproductive unit capable of giving rise to a new individual without sexual fusion, characteristic of lower plants, fungi, and protozoans

  Contagious disease - diseases spread by direct contact
• Describe what is meant by direct transmission and indirect transmission of a pathogen, describe 2 clear examples (mode of transmission and pathogen) of each and describe 2 examples which could be argued to be either direct or indirect transmission.

  Direct - pathogen transferred directly from one organism to another

  Direct contact

  Inoculation (by bite)

  Indirect - pathogen transferred indirectly

  Droplet infection

  Fomites (inanimate objects e.g. bedding)

  Vectors

  Unclear - inoculation (bite direct and needles indirect)
• State the transmission methods for the following plant diseases: ring rot, tobacco mosaic virus, potato blight, black sigatoka


  Ring rot - Direct contact, soil contamination, humans as vectors

  Tobacco mosaic virus - Direct contact, soil contamination, humans as vectors

  Potato blight - spores in water, soil, direct contact

  Black sigatoka - spores carried by wind, soil, direct contact
• State the transmission methods for the following animal diseases: tuberculosis, bacterial meningitis, AIDS, Influenza, Malaria, Ring worm, Athlete's foot

  Tuberculosis - Droplet infection

  Bacterial meningitis - direct contact with bodily fluids

  AIDS - Inoculation through break in skin

  Influenza - droplet infection

  Malaria - Vector - mosquitoes

  Ring worm - Skin to skin contact

  Athlete's foot - contact with infected skin or fungus in environment
• Describe and explain 7 factors that affect the transmission of communicable diseases in animals

  Overcrowded living and working conditions - More chance for contact + droplet infection

  Poor nutrition - weaker immune system

  Compromised immune system - weakened defences

  Poor disposal of waste - breeding sites for vectors and pathogens contaminating water supplies

  Climate change - Vectors spreading - mosquitoes can spread over larger area

  Culture and infrastructure - traditional 'medicine', FGM, Lack of clean water, traditional burials, roads, fast diagnostics, research

  Socioeconomic factors - lack of trained health professionals, Insufficient public warning/advice/education on prevention
• Describe and explain 6 factors that affect the transmission of communicable diseases in plants

  Planting crop varieties that are susceptible to disease - larger population of pathogen able to infect less susceptible varieties

  Overcrowded growing - increases likelihood of contact, increased humidity due to lack of air flow causes increased fungal growth

  Poor mineral nutrition - reduces resistance

  Damp, warm conditions, increase survival and spread of pathogens

  Climate change - increased rainfall - humidity, animal vectors move to new areas

  Monoculture practices - lack of variation - all susceptible to disease so spreads easily

  Plant cloning practices - lack of variation - if one susceptible, all susceptible
• State 3 examples of barriers to pathogens in plants

  Waxy cuticle, cell wall (cellulose), bark
• Describe the major difference between plants' response to pathogens as compared to animals' response to pathogens, and explain why this is a possible successful strategy for plants.

  Not specific - aims to destroy pathogen or close off infected area to prevent spread

  Plants able to lose parts of themselves and survive
• Describe ways in which a plant cell can detect the presence of a pathogen


  Detect chemicals on surface of pathogens

  Detect break down products of cell wall - beta glucose

  Cells have receptors on plasma membranes - once activated send chemical signals to nucleus to switch on defence genes. Chemicals also sent to other cells via plasmodesmata to initiate defence genes in other cells in preparation for incoming attack.
• Name two molecules produced by plants to limit the spread of the pathogen

  Lignin

  Callose
• Describe the structure of callose

  Poly saccharide of beta glucose but with 1-3 and 1-6 glycosidic bonds so a different shape to cellulose
• Describe 4 ways callose is used to limit the spread of a pathogen

  Deposited under cell wall between wall and plasma membrane - pathogen's cellulose digesting enzymes will not fit so they cannot digest it

  Production continues after end of infection - investing in defence.

  Seal off sieve plates in phloem to infected area to stop spread

  Fills plasmodesmata between infected cells and neighbours to stop spread
• List 6 different types of plant chemical defences, and for each describe their role and give examples

  Insect repellents - pine resin

  Insecticides - caffeine, nicotine

  Antibacterial - phenols

  Antifungal - chitinases

  Anti-oomycetes (anti-protoctists) glucanases

  General toxins - cyanide
• Define the term "non-specific defences"

  Not targeted - work against all pathogens in the same way
• State 4 barriers the human body has to minimise the entry of pathogens into our cells

  Skin, Mucous membranes, Stomach acid, Blood clotting
• Explain how the skin acts as an effective barrier to the entry of pathogens

  Sheds off - loses pathogens as well

  Dead cells in surface layer - cannot be hosts for pathogens esp. viruses

  Produces sebum - inhibits pathogen growth

  Skin flora - bacteria that compete for space and nutrients
• Explain how mucous membranes act as an effective barrier to the entry of pathogens

  Mucus traps pathogens

  Cilia move mucus out/swallow

  Mucus has lysosyme - digestive enzyme breaks down bacterial and fungal cell walls

  Mucus has phagocytes
• Name 4 expulsive reflexes and explain their value for protection against pathogens

  Coughing, sneezing, vomiting, diarrhoea

  Expel mucus and contents of gut including any pathogens
• Draw a flow chart to show the process of blood clotting

  Tissue is damaged

  Platelets are activated by damaged tissue

  Platelets release the enzyme thromboplastin (they also release serotonin which makes smooth muscle in walls of blood vessels contract causing them to narrow and reduce blood loss)

  In the presence of calcium ions (and vitamin K) thromboplastin catalyses the conversion of prothrombin into thrombin

  Thrombin, an enzyme, catalyses the conversion of fibrinogen (a soluble globular protein) into fibrin (an insoluble fibrous protein)

  Fibrin molecules form a mesh

  The fibrin mesh traps platelets and red blood cells to form a clot

  The clot dries out to form a hard tough scab

  The clot and scab minimise blood loss and minimise entry of pathogens directly into tissues or the blood through broken skin

  
• Explain the importance of blood clotting and the release of serotonin by platelets

  The clot and scab minimise blood loss and minimise entry of pathogens directly into tissues or the blood through broken skin

  Platelets release serotonin which makes smooth muscle in walls of blood vessels contract causing them to narrow and reduce blood loss
• Describe the processes involved in the inflammatory response and explain their value for protection against pathogens

  Damaged tissue/pathogens detected by mast cells - release histamine and cytokines

  Red - dilation of blood vessels, increased blood flow

  Swollen - gaps in capillaries widen - 'leakier'

  Pain - Sensitising nerve endings in skin - makes body protect already damaged areas

  Hot - due to greater blood flow - reduces reproduction of pathogens

  Pus - tissue fluid containing many dead WBC - attracted to the region by cytokines, increased blood flow and able to get out of leaky capillaries
• Describe how fever is initiated in response to invasion by pathogens and explain its value for protection against pathogens

  Cytokines make hypothalomus maintain a high body temp

  Specific immune response works faster at higher temp

  Pathogens optimum temp is normal body temp s fever inhibits reproduction