natural selection

• 
  

  Adaptations:

  • behavioural
  • anatomical
  • physiological
• behavioural: actions which help them survive and reproduce
• anatomical: structures observed or seen when dissected

  • white fur on bear = camouflage
• physiological: internal workings to help survive and reproduce

  • mosquitos produce chemicals to stop animal blood clotting
• natural selection: causes evolution to occur

  1. random mutation occurs
  2. produces advantageous allele to survive and reproduce, pass onto offspring
  3. causes change in frequency of alleles in offspring population
• selective pressure: individuals may die or fail to reproduce due to lack of resources
• Describe how DDT-resistance becomes widespread in some mosquito populations (4)

  random mutation allowed for resistance

  most mosquitos get killed by DDT

  those resistant have advantageous allele so can survive and reproduce

  pass on allele to offspring

  overtime frequency of alleles will change
• Aseptic technique:

  • flame neck of bottles - prevent microbes entering/ contaminating broth
  • work near bunsen burner - create upward current to prevent microbes from air entering dish
  • seal in two places - allow O2 to enter = aerobic respiration = discourage harmful bacteria growth
  • incubate at 25 - avoid harmful growth of bacteria
  • sterilise equipment- put through flame
• aseptic techniques: prevent contamination and provide a more reliable and valid set of results allowing for comparison
• types of selection:

  • directional
  • stabilising
• directional selection:

  • favours allele with extreme characteristic (phenotype)
  • original population = few resistance
  • new population = more resistance to survive and reproduce

  
• stabilising selection:

  • individuals towards middle range more likely to survive and reproduce
  • E.g baby weight , small baby = not survive = can't maintain body temp
  • big babies less likely to survive = too big to fit through pelvis

  
• describe and explain three ways in which the scientist would ensure he used aseptic techniques to move each cube of agar onto new agar plate (3)

  wash hands to remove microbes

  flame equipment to sterilise/kill microbes

  work near bunsen burner to create upward current of air to prevent microbes entering dish from air
• Suggest why the number of E. coli cells per mm3 in each culture after 24 hours might have been lower if the student had not used a sterilised pipette. Explain your answer (2)

  different bacteria produced

  bacteria could have produced toxins