VirusVaccineScientificInstrumentRespSystemPhotosynthesis

• Viruses:

  • Tiny, smaller than bacteria
  • Contain DNA (or RNA) inside
  • Usually have a protein coat on the outside (capsid)
• Viruses by themselves:

  • Do nothing
  • Cannot reproduce by themselves
  • Don't perform metabolic activities
  • Don't grow
  • Don't eat nor make food
• Viruses need host cells:

  • Viral nucleic acids take control of the host cell
  • Viruses enter by using surface enzymes to bore into the cell or using a "trojan horse" method
  • Direct the host cell to produce more viruses
  • Host cell consumes its own parts in making viruses, usually leading to the death of the host cell (lytic cycle)
• Some viruses can hide in host cells:

  • Virus DNA joins the host cell's DNA
  • Viral DNA multiplies with the host DNA without harming the cell (lysogenic cycle)
  • Viral DNA may lay quiet for many host cell generations until triggered by stress, heat, or cold to become active and attack/kill its host (lytic cycle)
• How viruses cause disease:

  • Cells usually die by bursting at the end of the lytic cycle, releasing countless new viruses to attack other cells
  • Host DNA may mutate when viral DNA inserts itself, potentially causing cancer
  • Host immune systems produce antibodies to inactivate viruses and attract white blood cells to phagocytize the virus
• Vaccines:

  • Contain dead or weakened viruses
  • Examples of viral vaccines: rabies, smallpox, polio, chickenpox, flu
• Viral adaptation to host defenses:

  • Viruses mutate, changing their DNA and surface proteins to avoid recognition by the immune system
  • New vaccines must be developed for mutating viruses
  • Some viruses hide in host cell DNA or elsewhere within cells
• Rabies:

  • Spread by contact with infected animal saliva
  • Can be prevented via a series of painful vaccinations after an animal bite
  • Nearly always fatal if symptoms begin
  • Commonly spread by rabid bats, skunks, raccoons, and dogs
• Bird Flu:

  • Spreads easily among birds but is hard for humans to catch
  • Often fatal to humans
  • Potential for a serious worldwide pandemic if a form develops that transmits easily from person to person
• Gas exchange in plants:

  • Plants take in air through stomates on the underside of leaves
  • CO2 is taken in for photosynthesis, and oxygen is taken in during the night for cell respiration
• Gas exchange in animals:

  • Respiration results in gas exchange between the environment and the body's cells
  • Breathing includes inspiration and expiration
  • Diffusion through moist membranes is how gas exchange occurs
  • Some animals use skin for respiration, while larger ones require gills or lungs