Required Practical:Sampling Organisms

• What should you be able to describe by the end of the video?

  How to measure the population size of a common species and how to use sampling techniques to investigate the effect of a factor on the distribution of this species.
• What is the purpose of random sampling in estimating population size?

  • To obtain a representative sample of the species
  • To minimize bias in the selection of sampling locations
• What equipment is used for random sampling?

  A quadrat.
• What are the dimensions of the quadrat used in the practical?

  0.5 meters by 0.5 meters.
• How do students select random sampling points in the practical?

  By drawing numbers from a bag corresponding to points on tape measures.
• How many samples should students take in the practical?

  Ten samples.
• What is the formula to estimate the total population size of daisies?

  Total population size = (Total area / Area sampled) × Number of organisms counted
• What is the total area of the field in square meters?

  400 square meters.
• What is the area sampled when using the quadrat?

  2.5 square meters.
• How many daisies were counted in the sample?

  300 daisies.
• Why is the total population size of daisies considered an estimate?

  Because the sampled quadrats may not represent the entire area accurately.
• What should be done if the initial quadrat throws do not represent the whole area?

  • Increase the number of quadrat throws
  • Cover a greater percentage of the area
• What factor is being investigated in relation to the distribution of daisies?

  Light intensity.
• What is used to measure light intensity in the practical?

  A light meter or an app.
• How do students measure the change in the number of daisies in relation to the tree?

  • Place a tape measure from the tree
  • Use a quadrat to count daisies at intervals along the tape measure
  • Record light intensity at each point
• Why might there be a greater number of daisies further from the tree?

  Because there is lower light intensity under the tree.
• What is another abiotic factor that might affect the number of daisies?

  Water and minerals absorbed by the tree.