Practical - Sampling Techniques - Quadrats (OCR Gateway GCSE Biology: Combined Science)

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Ecological Sampling with Quadrats

  • Ecology is the branch of biology that studies the distribution and abundance of species, the interactions between species, and the interactions between species and their abiotic environment
  • Ecologists are biologists that study these interactions by investigating ecosystems
  • One piece of equipment that is routinely used to investigate population size is a quadrat


  • Quadrats are square frames made of wood or wire
  • They can be a variety of sizes eg. 0.25m2 or 1m2
  • They are placed on the ground and the organisms within them are recorded
  • Plants species are commonly studied using quadrats to estimate the abundance

Quadrat in use, downloadable IGCSE & GCSE Biology revision notes

Using a quadrat to investigate population size or distribution

  • Quadrats can be used to measure abundance by recording:
    • The number of an individual species: the total number of individuals of a single species (eg. buttercups) is recorded
    • Species richness: the total number of different species (but not the number of individuals of each species) is recorded
    • Percentage cover: the approximate percentage of the quadrat area in which an individual species is found is recorded (this method is used when it is difficult to count individuals of the plant species being recorded eg. grass or moss

Estimating percentage cover of one or more species, downloadable IGCSE & GCSE Biology revision notes

How to estimate percentage cover of one or more species using a quadrat

Investigating population size in 2 different areas using quadrats


  • 2 tape measures
  • Quadrat
  • Random number generator
  • Species identification key

MethodRP Ecosystems_ Estimating Population Size Method (1)_1, downloadable IGCSE & GCSE Biology revision notesComparing population sizes across 2 different study areas 2, downloadable IGCSE & GCSE Biology revision notes

How to estimate the population size of a plant species in a survey area. You must repeat steps 1-5 in the second study area.


  • Once the results have been collected and the averages calculated, we can compare the abundance of the study species in each survey area
  • Species abundance is likely to be influenced by biotic factors such as:
    • Competition
    • Predator-prey relationships
    • Interactions with other organisms within the food chain or food web
  • The abundance will also be influenced by abiotic factors such as:
    • Light intensity
    • Mineral availability
    • Water availability
    • pH
    • Temperature
    • Salinity


  • It can be easy to miss individual organisms when counting in a quadrat, especially if they are covered by a different species
    • Solution: Use a pencil or stick to move leaves carefully out of the way to check if there is anything else underneath
  • Identifying species may be tricky
    • Solution: Use a species identification key to identify the species
  • Sometimes, certain species of plants are too numerous to count
    • Such as grass plants in a quadrat 
    • Solution: Use notation such as >100 or >>100
      • Which mean 'greater than 100' or 'much greater than 100'
    • If an approximate number is needed, use ∼
      • eg. ∼30 means 'approximately 30'

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Author: Phil

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.