Free Science Lessons

• Random sampling


  Areas that we take samples from are selected by using random numbers
• Random sampling


  • Reduces the chance of sampling bias
  • Random numbers can determine the coordinates on a map
• Non-random sampling


  There are three types: opportunistic, stratified, and systematic
• Opportunistic sampling


  Scientists select the organisms that are readily available
• Opportunistic sampling


  • Organisms may not be representative of the whole habitat
  • Makes opportunistic sampling unreliable
• Stratified sampling


  The population is divided into subgroups or strata
• Stratified sampling


  • Need to ensure the number of samples from each subgroup is representative
  • More reliable than random sampling
• Sampling insects in a field

  1. Use a sweeping net

  2. Use a pooter
• Systematic sampling


  Used when there's a gradual change in the habitat from one place to another
• Sampling ground-level animals


  Use a pitfall trap
• Line transect


  1. Measuring tape placed across habitat

  2. Any organism touching the tape is sampled
• Sampling tiny animals in soil

  Use a Tullgren funnel
• Belt transect


  1. Two parallel tapes placed across habitat

  2. Any organisms found between the tapes are sampled
• Sampling bottom-dwelling animals in a river

  Use kick sampling
• Interrupted belt transect


  Organisms sampled at regular intervals along the transect
• Sampling slow-moving or static animals on a seashore

  Use a frame quadrat
• Density


  The actual number of a plant species counted per unit area (e.g. per m²)
• Percentage frequency


  The number of small squares within a quadrat that contain the plant, reported as a percentage
• Abundance


  The estimated number of organisms in a given area
• Percentage cover


  An estimate of the percentage of the total quadrat area occupied by a plant
• Sampling a large number of organisms increases the reliability of the sampling
• Sampling plants using a quadrat


  Place the quadrat in multiple positions and calculate a mean
• Sampling plants using a point quadrat

  Position a wooden bar with holes over the ground, insert metal pins into the holes, and count any plants touched by the pins
• The Earth is rich in habitat biodiversity, species biodiversity and genetic biodiversity
• This rich biodiversity is under threat from human activity
• The population of humans on Earth was 3 billion people


  1960
• The population of humans on Earth had reached 8 billion


  2022
• An increasing human population presents a major challenge to the biodiversity on Earth
• Feeding a large human population

  • Requires intensive farming methods
  • Leads to the destruction of forests
• Human activity


  • Requires a great deal of space
  • Leads to the destruction of forests
• Carbon dioxide from burning fossil fuels


  Leads to climate change
• Monoculture


  A field containing only one crop species
• Monocultures have an extremely low level of biodiversity
• Herbicides are used to kill unwanted plant species in monocultures
• Pesticides are used to kill insects that might eat the crop in monocultures
• Monocultures are often grown on enormous fields to make harvesting more efficient
• Hedgerows are dug up to create large monoculture fields
• Hedgerows contain a rich diversity of plants and animals
• Forests are cleared to provide land for farming, including tropical rainforests
• Tropical rainforests contain more than half of all animal and plant species on Earth