A2 EMPA 2014 prep

Created by: Gege
Created on: 30-04-14 19:15

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A2 EMPA
- Nutrient cycles
  - Carbon cycle
    - All organisms need carbon to make essential compounds
    - Carbon in the form of carbon dioxide is absorbed by plants when they photosynthesise. This becomes carbon compounds
    - Carbon is passed on when primary consumers eat plants; when secondary and tertiary consumers eat other consumers
    - The carbon compounds in dead organisms are digested by saprobiotic organisms or decomposers (e.g. bacteria and fungi)
      - If there are no decomposers, the carbon compounds can be turned into fossil fuels over millions of years by heat and pressure
        The carbon in fossil fuels is released when they are burnt - combustion
    - Carbon is returned to the atmosphere as all living organisms respire
  - Nitrogen cycle
    - Nitrogen is needed by animals and plants to make proteins, RNA and DNA
    - They cannot use atmospheric nitrogen - this must be converted to nitrogen compounds first by bacteria
    - 1. Nitrogen fixation: nitrogen in atmosphere is converted to ammonia by mutualistic nitrogen-fixing bacteria (found in root nodules of plants). The plants gain nitrogen compounds; the bacteria gain carbohydrates
      - The nitrogen compounds are passed on to animals when they feed on plants
    - 2. Ammonification: nitrogen compounds from dead organisms/animal waste (urine and faeces) are turned into ammonium compounds by decomposers
    - 3. Nitrification: ammonium compounds in the soil are converted to nitrogen compounds that can be used by plants. Ammonium to nitrites, then nitrites to nitrates by nitrifying bacteria
    - 4. Denitrification: nitrates in the soil are converted to atmospheric nitrogen by denitrifying bacteria under anaerobic conditions (e.g. in waterlogged soils)
    - Leaching is when nutrients are removed from the soil (usually by washing away by rain). Leaching of nitrogen fertiliser into rivers/ponds can cause eutrophication
- Investigating populations
  - Abundance
    - The number of individuals of a particular species in an area
    - Count the number of individuals
    - Count the number of samples a species has been recorded in - frequency. e.g. 70% of samples
    - How much of the area being investigated is covered by a species - percentage cover (plants only)
  - Mark-release-recapture
    - Measures abundance of more mobile species
    - Total population size = (no. caught in 1st sample x no. caught in 2nd sample) / no. marked in 2nd sample
    - Capture sample using appropriate technique, e.g. pitfall trap
    - Mark each individual in a way that is non-toxic and doesn't affect chances of survival
    - Release back into habitat, then take a second sample a week later and count the number of marked individuals in this new sample
  - Distribution
    - Where a particular species is within the area being investigated
- Survival and response
  - Taxis
    - Organisms move towards (positive taxis) or away from (negative taxis) a directional stimulus
    - Increases chance of survival
      - Avoids predators
      - Find food
      - Conserve water
  - Kinesis
    - Organism's movement is affected by a non-directional stimulus, e.g. light intensity
    - Movement to more favourable conditions; away from unfavourable conditions