Biology Required practicals

• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

  3. Person 2 holds a ruler vertically with the 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch the ruler

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  Time taken for a person to respond to a stimulus
• The two people then switch places with Person 1 testing the reaction time of Person 2
• Independent variable


  The variable that is changed in an experiment
• Dependent variable


  The variable that is measured for each change in the independent variable
• Control variables


  • Variables that are kept constant to avoid affecting the dependent variable
  • Examples: distance between thumb and first finger, measuring at top of thumb, room conditions
• Other independent variables that could be investigated: effect of practice, dominant vs non-dominant hand, effect of chemicals like caffeine
• Need to check for any medical issues that could be affected by chemicals given to test subjects
• Experiments should be carried out in a lab where hazardous chemicals are not normally used
• Measuring population size of a common species in a habitat

  1. Use random sampling with quadrats

  2. Place two 20m tape measures at right angles

  3. Select random numbers to determine quadrat placement

  4. Count number of organisms in each quadrat

  5. Estimate total population using formula
• Using sampling techniques to investigate the effect of a factor on the distribution of a species

  1. Place transect line from tree outwards

  2. Use quadrats to count organisms at intervals along transect

  3. Measure light intensity at each quadrat location

  4. Analyse how organism count changes with distance from tree
• Quadrats


  • Come in a range of different sizes
  • Used to sample a small area and count organisms
• Random sampling


  Using random numbers to determine quadrat placement
• Total population size


  Calculated as: Total area / Area sampled * Number of organisms counted
• Increasing the number of quadrat samples can improve the estimate of total population size
• Transect line


  Line placed to measure how a factor (e.g. light intensity) changes with distance
• Light intensity is an abiotic factor that can affect the distribution of plant species
• Other abiotic factors like water and mineral availability can also affect plant distribution