OCR A Level Biology- Communicable Diseases

• What parts of the plant does Ring Rot damage?

  Leaves, tubers and fruit
• What causes a communicable disease?

  A pathogen
• What are the 4 main types of pathogen?

  1. Bacteria

  2. Viruses

  3. Protoctista

  4. Fungi
• What does a vector do?

  Carry pathogens from one organism to the other
• How are communicable diseases in plants spread?

  Directly plant-to-plant
• What proportion of bacteria cause communicable disease?

  Only a small proportion
• What are the two main ways bacteria are classified?

  1. By shape

  2. By cell wall
• What shape are bacilli?

  Rod-shaped
• What is chain of bacteria called?

  Strepto-species type

  i.e. Streptobacilli
• What is a cluster of bacteria called?

  Staphylo-species type

  i.e. staphylococci
• What shape is a vibrios?

  Comma shaped
• What is a corkscrew-shaped bacterium called?

  Spirochaetes
• What shape is a coccus?

  Spherical
• What are the two types of bacterial cell wall?

  Gram-positive and gram-negative
• What colour do gram-positive bacteria go with gram staining?

  Purple-blue
• What colour do gram-negative bacteria go with gram staining?

  Red
• What are some features of a gram-positive cell wall (excluding colour with gram staining)


  Thicker but less tough, more susceptible to antibiotics which damage the cell wall, more peptidoglycan, lower lipid content, more prominent mesosome
• What makes a gram-positive cell wall go purple-blue with gram staining?

  The peptidoglycan in their cell wall retains crystal violet stain
• What are some features of a gram-negitive cell wall (excluding colour with gram staining)?

  Thinner but tougher, higher lipid content due to outer cell membrane, less susceptible to antibiotics
• What is an example of a bacterium with a gram-positive cell wall?

  MRSA
• What is an example of a bacterium with a gram-negative cell wall?

  E.coli
• What is a bacterial cell wall mostly made up of?

  Peptidoglycan
• What is the structure of peptidoglycan?

  Massive disaccharide polymers cross-linked by short chains of identical amino acid monomers
• What is the basic structure of any virus?

  Some genetic material (either DNA or RNA) surrounded by a protective protein coat
• What is the mechanism of infection of a virus?

  They attach to the cell and inject their genetic material, which takes over the biochemistry of the host cell to make more viruses by inserting itself into the host DNA, until so many are made that the host cell is lysed (bursts) and the new viruses are released
• What 2 things make viruses very successful pathogens?

  They reproduce rapidly and evolve by developing adaptations to their host
• What proportion of naturally occurring viruses are pathogenic?

  All of them
• How many other types of organism do viruses infect?

  Every other type of organism, including other viruses
• What is a bacteriophage?

  A virus which attacks a bacteria
• What is a virophage? Give an example

  A virus which infects other viruses, such as the Sputnik virus
• Are protoctista eukaryotic or prokaryotic?

  Eukaryotic, with a wide variety of feeding methods
• What proportion of protoctista are pathogenic?

  Only a small percentage, most are harmless
• What are fungi a major problem for?

  Some plants- they tend not to be a major problem for animals
• Are fungi eukaryotic or prokaryotic?

  Eukaryotic
• Are protoctista unicellular or multicellular?

  Unicellular, although they can group into colonies
• Are fungi unicellular or multicellular?

  Usually multicellular, with the exception of yeasts
• How do fungi feed?

  Many are saprophytes, but the pathogenic ones are parasites and eat living organisms. They can't photosynthesise, so digest food outside of their cells before absorbing the nutrients
• What do saprophytes feed on?

  Dead and decaying matter
• What part of a plant do many plant fungal diseases affect?

  The leaves, stopping the plant photosynthesising and killing it rapidly
• How do fungi reproduce?

  They produce millions of spores, which can spread huge distances and spread their disease quickly among crops