biology required practicals

• control variable- keep the same

  dependant variable- measure

  independant variable- change
• reaction time practical

  1. hold a ruler between a persons thumb and index finger lined up with the 0cm mark.
  2. drop the ruler without warning and record the distance dropped before it was caught.
  3. calculate reaction time
  4. carry out repeats
  5. introduce a variable such as before and after a sugary drink
• quadrats-

  1. place 1m2 quadrat in a random grid position in an area and count organisms
  2. calculate the mean number per m2 then multiply by total area to give an estimate of total population
  3. to observe variation in population density over distance move quadrat along a transect and record number per m2
  4. plot population density against distance
• microbiology-

  produce bacteria cultures using aseptic techniques

  1. sterilise equipment using a flame every time they are used
  2. open petri dish towards flame and add drops of different bacteria cultures on the agar or spread one across the whole plate.
  3. label the dish with names of bacteria and antibiotics
  4. seal with a few bits of tape but still allow air and incubate
  5. measure the diameter of bacteria colonies or areas where no bacteria are if testing antibiotics. calculate area of circled
• germination practical-

  observe geotropism in roots or phototropism in shoots of plants

  1. put cress seeds on damp cotton wool in a petri dish
  2. allow to germinate in a dark environment
  3. if observing root growth stand dish on its side after a few days you should see roots growing downwards (geotropism)
  4. if observing shoot growth allow a bit of light to enter through a hole and measure shoot height every day. you will see they bend towards the light (phototropism)
• decay-

  determine relationship between temperature and rate of decay

  1. measure volume of whole milk using a syringe put in a test tube and add sodium carbonate
  2. add the indicator phenolphthalein which is pink for a ph over 8.3
  3. use a water bath to change temperature, measured using a thermometer in the test tube
  4. add the enzyme lipase and start the stop watch
  5. record the time taken for the indicator to decolourise (white).
  6. repeat for different temperature
  7. an increase in temp will increase the rate of decay up to the point at which the enzyme denatures