B5 - Communicable Diseases


Growing Bacteria in the Lab

Binary Fission = When bacteria reproduces by dividing

Culture Nutrient Medium = Substance that contains nutrients for the bacteria

Mutation = When DNA inside the cell accidentally changes when the cell divides

Sterilise = When you kill off all of the microbes on the thing/equipment

Inoculate = Treat with a vaccine to produce immunity against a disease

Contaminate = When there are things, that we don’t want, inside something


1. Sterilise wire loop > put in alcohol then put in flame until it glows red 2. Open bacteria near flame > sterilise bottle neck then put in flame 3. Put sterile wire loop in bacteria 4. Hold Petri-dish near flame and open it > Open it for as little time as possible 5. Create a “zig-zag” pattern on agar jelly > smear not poke 6. Place antibacterial paper on agar jelly 7. Close Petri-dish then tape it 8. Incubate at the ideal temperature > not human body temperature



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More About Plant Diseases

Plant Pathogens:


  • Have sharp mouthparts that penetrate into the phloem vessels so they can feed on the sugar-rich phloem sap
  • Attack in huge numbers, depriving the plant cells of the products of photosynthesis
  • Act as vectors (something that spreads infection)
  • Can be destroyed using chemical pesticides or biological pest control (enclosed spaces > greenhouse)

Mineral Deficiency > non-communicable diseases in plants:

  • plants need a good supply of nitrate ions from the soil to convert the sugars made in photosynthesis. If thereis nitrate deficiency in the soil, protein growth will be limited, and the plants will not produce a crop properly
  • plants take magnesium ions from the soil to make chlorophyll needed for photosynthesis, If the level of magnesium ions in the soil is low, the plant cannot make enough chlorophyll. The leaves become yellow and growth slows down bvecause plants cannot photosynthesise fully. The yellowing of the leaves is known as Chlorosis.



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Detecting Disease

Stunted Growth = nutrient deficiency

Spots on leaves = black spot fungus on roses

Areas of decaying or rotting = black spots on roses, blights on potatoes

Growths = crown galls caused by bacterial infections

Malformed stems and leaves = due to aphid or nematode infestation

Discolouration = chlorosis, tobacco mosaic virus

Prescence of visible pests = aphids or caterpillars

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Plant Defence Responses

Physical Barriers:

  • Cellulose cell wall that strengthens plant cells, also helps to resist invasion by microorganisms > this is why aphids are so damaging because if they pierce the cell wall  it givesd pathogens an easy way in
  • The tough waxy cuticle on the surface of leaves acts as a barrier to the enrty of pathogens
  • Bark on trees is hard to penetrate and when it falls off the pathogen alls off as well
  • Leaf fall = any pathogens that infect the leaves fall off as leaves are lost

Chemical Barriers:

Scientists are increasingly investigating plant antibacterial chemicals to see if they can be adapted for use as antibiotics against humans pathogens. Mint and witch hazel are often used as mild antiseptics in cosmetics and over-the-counter medicines.

Defence agaisnt herbivores:

  • Poisins = to deter herbivores > foxgloves, deadly nightshade, yew
  • Thorns = makes it painful for herbivores to eat them
  • Hairy Stems/ Leaves = stops  herbivores eating/ laying eggs on them
  • Drooping/curling when touched = to collapse and catch the herbivore
  • Mimicry = when pants droop to mimic dead plants
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