Distribution of Organisms and Sampling Tecniques

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  • Created by: Lina
  • Created on: 09-04-14 13:26

Using Quadrats to study the distribution of organi

  • Place a quadrat on the ground at a random point within the first sample area- put measuring tapes along the 2 sides and choose random coordinates using a random number generator
  • Count all the organisms within the quadrat
  • Repeat these steps as many times as you can in one area
  • Work out the mean number of organisms per quadrat within the first sample area
  • Repeat the steps in the second sample area
  • Compare the 2 means
  • Because the coordinates are chosen at random, you will make sure that there is no bias by the investigator
  • Ensures the results are valid, as they are reliable (repeatable+ reproducible) + answer the original question
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Working out population size

  • Work out the mean number of organisms per m2
  • Multiply the mean number of organisms per m2
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Using Transects to study the distribution of organ

  • Choose the start and the end position of the transect, which should be placed across the steam
  • Determine the direction+ length of the transect
  • Mark out a line in the sample area using a tape measure
  • Place quadrats along the line either next to each other or at intervals
  • Count the number of organisms in each quadrat
  • Perform parallel transects to ensure the results are reliable- repeatable+ reproducible, as the sample size increases- more representitive of the whole population
  • Calculate the mean of the number of organisms in the quadrats parallel to each other
  • Compare the results of sample areas
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Why would it be very consuming to just count every

  • The organisms may move
  • There may be too many organisms to count
  • Time- consuming
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How to improve an experiment

  • Reliability- making sure the results are repeatable and reproducible (other people using different equipment should get the same results)
  • Large sample size- representative of the whole population
  • Random samples- not biased- results shouldn't be taken in one spot
  • Validity- reliable and answer the original question
  • Control the variables
  • Accuracy- results that are close to the true answer
  • Precision- results that are really close to the mean
  • Resolution- the smallest change a measurement instrument can detect
  •  Zero error- if a systematic error is caused by using equipment that isn't calibrated properly
  • Systematic error- the same error is made every time
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