p2 required practicals

• what is the independent variable in the random sampling practical?

  the habitat
• what is the dependent variable in the random sampling practical?

  • number of species
  • percentage cover of one particular species
• what is the independent variable in the reaction times practical?

  left/right hand to see if dominant is faster
• what is the dependant variable for the reaction times practical?

  distance on ruler when caught
• control variables in reaction time practical?

  • minimise distractions
  • height dropped from - line up 0cm of the 1m ruler with their hand
  • distance between first finger and thumb - use ruler to kepp constant
• why do people have faster reaction times with their dominant hand?

  this is not a reflex. it is a learned action, so more likely to be faster with dominant hand
• how could you improve the reflex experiment increase the accuracy?

  use a computer programme where you touch a button when the screen changes, rather than testing with a ruler
• how could you improve the reflex experiment to increase the precision?

  carry out repeats

  discard anomolies

  calculate mean
• possible sources of error in the reaction time practical

  • consistency - either use top or bottom of finger to find distance
  • ear muffs to reduce distractions
  • have finger and thumb far enough apart to reduce likelihood of ruler hitting hand on fall
  • leave gaps between tests to reduce effect of practising
• is testing reaction times a reflex action?

  no as electrical impulses go to conscious part of brain
• method of reaction times experiment?

  • person sits in chair with arm over table
  • use short ruler to measure set distance between first finger and thumb (5cm)
  • line up the 0cm of the 1m ruler with their hand
  • without warning, drop the 1m ruler
  • record the distance on the ruler at the point they catch it
  • repeat and find mean
  • convert this into a reaction time
• what does representative mean?

  only sampling a small percentage of the whole habitat

  so the trend in sample must match the trend of the whole population
• control variables in the field work practical?

  • same area quadrat
  • same method of counting
• possible sources of error in field work experiment?

  • possible miscounting if plants grow close together
  • could misidentify plant species
  • estimating % cover is subjective
• advantages of line transect method over random sampling?

  • less prone to bias
  • can see effect of change of an abiotic conditions when move across a habitat
• disadvantages of line transects over random sampling?

  • more time consuming
  • could miss out plants between samples by chance -so dta wouldn't be representative
• ways of making data more representative in line transect?

  • complete several transects and calculate mean
  • can reduce gaps between samples
  • or continuous line belt transect with no gaps
• when should you use a line transect?

  when seeing if there is change in species when moving across a habitat
• how can plants adapt to surviving being trampled?

  growing flat on ground
• what abiotic factors could you measure for line transect?

  • wind speed
  • soil pH
  • light intensity
  • soil depth
  • soil moisture
• what biotic factors could you measure for line transect?

  % cover of plants

  no. species present
• indpendant variable for line transect?

  distance
• explain the problems caused by repeating the tests with one volunteer in the short period of time

  they improve with practise

  so results less repeatable
• method for line transect?

  • place tape measure across field
  • place quadrat at 0m of tape measure
  • record light intensity (or factor)
  • then count number of species or % cover of one type of plant
  • repeat at regular intervals down transect (eg every 2m for a 20m transect)
  • repeat whole process at different area of field
• when should you estimate % cover of plants?

  when it is difficult to count exact number
• why are random coordinates used rather than choosing where to place a quadrat?

  choosing where to place quadrat creates bias

  and therefore not representative
• when is random sampling appropriate?

  to compare abundance of plants in 2 different habitats
• how to estimate % cover?

  • if quadrat is divided into 25 squares, then each square covers 4% of total
  • estimate how full each square is (0%is empty and 4% is full)
  • then add up total values for each of the 24 squares