GCSE AQA Biology 2 Distribution of organisms

The environment
1. Habitat: The place where an organism lives
2. Distribution of an organism: Where an organism is found
  1. Affected by environmental factors...
    1. Temperature
    2. Availability of water
    3. Availability of oxygen/carbon dioxide
    4. Availability of nutrients
    5. Amount of light
  2. Ways to study it...
    1. Measure how common organism is in 2 sample areas and compare
    2. Study how it changes across area
Quadrats
1. Quadrat: Square frame enclosing a known area e.g. 1m squared
2. To compare how common organism is in 2 sample areas...
  1. 1) Place quadrat on ground at random point in 1st sample area
    1. 2) Count all organisms within quadrat
      1. 3) Repeat steps 1 & 2 as many times as possible
        4) Work out mean no. of organisms per quadrat for 1st sample area
        5) Repeat steps 1 to 4 in 2nd sample area
        6) Compare the means
Working out population size
1. 1) Work out mean number of organisms per metre squared
  1. 2) Multiply mean by total area (in metres squared) of habitat
Transects
1. Can use to find out how organisms are distributed across an area...
  1. 1) Mark out line in area using tape measure
    1. 2) Collect data along the line by...
      1. a) counting all the organisms that touch the line (that are being studied)
      2. b) using quadrats - can be placed next to each other along line or at intervals
Collecting environmental data
1. Need to think about...
  1. Reliability
    1. Have to be repeatable and reproducible
    2. Use a large sample size
    3. Use random samples
  2. Validity
    1. For results to be valid they must...
      1. Be reliable
      2. Answer original question
    2. Must control all variables - can find out if difference in distribution is caused by environmental factor or not

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GCSE AQA Biology 2 Distribution of organisms

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