A2 EMPA 2014 prep

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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



This is amazing! Thanks :)

Cat Scott

Have you actually sat the EMPA then?

Leana Miah

have you done the written paper yet?

Charlie Tapley

puddles the monkey is gonna ******* get it the japanese kiddy fiddler


thanks Zoe! ;) in answer to Cat and Leana nope we have not (same class), we're sitting it tomorrow :O

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