GCSE AQA Biology 2 Distribution of organisms

GCSE AQA Biology 2 Distribution of organisms

1. The environment

   • Habitat: The place where an organism lives
   • Distribution of an organism: Where an organism is found
     • Affected by environmental factors...
       • Temperature
       • Availability of water
       • Availability of oxygen/carbon dioxide
       • Availability of nutrients
       • Amount of light
     • Ways to study it...
       • Measure how common organism is in 2 sample areas and compare
       • Study how it changes across area

2. Quadrats

   • Quadrat: Square frame enclosing a known area e.g. 1m squared
   • To compare how common organism is in 2 sample areas...
     • 1) Place quadrat on ground at random point in 1st sample area
       • 2) Count all organisms within quadrat
         • 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

3. Working out population size

   • 1) Work out mean number of organisms per metre squared
     • 2) Multiply mean by total area (in metres squared) of habitat

4. Transects

   • Can use to find out how organisms are distributed across an area...
     • 1) Mark out line in area using tape measure
       • 2) Collect data along the line by...
         • a) counting all the organisms that touch the line (that are being studied)
         • b) using quadrats - can be placed next to each other along line or at intervals

5. Collecting environmental data

   • Need to think about...
     • Reliability
       • Have to be repeatable and reproducible
       • Use a large sample size
       • Use random samples
     • Validity
       • For results to be valid they must...
         • Be reliable
         • Answer original question
       • Must control all variables - can find out if difference in distribution is caused by environmental factor or not