NITROGEN CYCLE

Doc Brown's Chemistry KS4 science GCSE/IGCSE/O level Revision Notes

PART E A description of the NITROGEN CYCLE

The nitrogen cycle is described in terms of the function of nitrifying bacteria, lightning and production of nitrogen oxides, function of denitrifying bacteria, action of nitrogen-fixing bacteria, part played by leguminous plants (legumes) in nitrogen fixation, bacteria decomposers, action of soil bacteria, plants absorbing nitrates from the soil. These revision notes on the nitrogen cycle, should prove useful for the new AQA GCSE chemistry, Edexcel GCSE chemistry & OCR GCSE chemistry (Gateway & 21st Century) GCSE (91), (9-5) & (5-1) science courses.

Index: A Reversible Reactions  *  B Reversible reactions and Equilibrium  *  C The Haber Synthesis of ammonia

D(a) The manufacture and uses of ammonia-nitric acid-fertilisers  *  D(b) Fertilisers-environmental problems

E The nitrogen cycle (this page)

Advanced A Level Notes - Chemical Equilibrium * Advanced A Level Notes - Nitrogen & Ammonia


PART E 6. The Nitrogen Cycle for the gaseous element N2(g)

  • Nitrogen is an extremely important element for all plant or animal life! It is found in important molecules such as amino acids, which are combined to form proteins. Protein is used everywhere in living organisms from muscle structure in animals to enzymes in plants/animals.
  • Nitrogen from the atmosphere:
    • Action of nitrifying bacteria, e.g. they function in the root nodules of certain plants like peas/beans (the legumes), can directly convert atmospheric nitrogen into nitrogen compounds in plants e.g. nitrogen => ammonia => nitrates which plants can absorb.
      • However, most plants can't do this conversion from nitrogen => ammonia, though they can all absorb nitrates, so the 'conversion' or 'fixing' ability might be introduced into other plant species by genetic engineering.
    • The nitrogen from air is converted into ammonia in the chemical industry, and from this artificial fertilisers are manufactured to add to nutrient deficient soils. However, some of the fertiliser is washed out of the soil and can cause pollution.
    • The energy of lightning causes nitrogen and oxygen to combine and form nitrogen oxides which dissolve in rain that falls on the soil adding to its nitrogen content.
      1. N2(g) + O2(g) ==> 2NO(g), then 
      2. then 2NO(g) + O2(g) ==> 2NO2(g) 
      3. NO2(g) + water ==> nitrates(aq) in rain/soil
      4. Incidentally, reactions 1. and 2. can also happen in a car engine, and NO2 is acidic and adds to the polluting acidity of rain as well as providing nutrients for plants!
  • Nitrogen recycling apart from the atmosphere:
    • Nitrogen compounds, e.g. protein formed in plants or animals, are consumed by animals higher up the food chain and then bacterial and fungal decomposers break down animal waste and dead plants/animals to release nitrogen nutrient compounds into the soil (e.g. in manure/compost) which can then be re-taken up by plants. 
  • Nitrogen returned to the atmosphere:
    • However, the action denitrifying bacteria will break down proteins completely and release nitrogen gas into the atmosphere.
  • -

  • More 'biological detail' of the NITROGEN CYCLE with reference to the above diagram so you can show an understanding of how nitrogen is recycled.
    • a) Nitrogen gas in the air (78%, ~4/5th) cannot be used directly by most plants and all animals.
      • No animals and only a few specialised plants can directly use the very unreactive nitrogen from air, but all plants nitrogen in some form to synthesise amino acids and proteins for growth and maintenance and for DNA in cell reproduction.
      • However, nitrogen can be changed into nitrogen compounds like nitrates which the plants can use.
      • Animals rely on plants or other animals in the food chain for their source of nitrogen compounds e.g. protein in grass, crops or other animals.
    • b) Action of Nitrogen-fixing bacteria living in root nodules of plants or in the soil, their function is to fix nitrogen gas from the atmosphere into a chemical form the plant can metabolise.
      • Leguminous plants like peas, lentils, clover and beans can absorb nitrogen from the air via their root nodules (swellings on the root surface) which contain enzymes capable of converting ('fixing') atmospheric nitrogen into soluble nitrate - a nutrient essential for amino acids, proteins and therefore plant growth.
        • Legumes and their root nodule bacteria are an example of mutualism (see section 3.19 b) because the plant root supplies the bacteria with carbohydrate food and minerals and the bacteria supplies the plant in the form of the nitrate ion.
        • The process of converting nitrogen in air into nitrogen compounds is sometimes called 'nitrogen fixation'.
    • c) The action of lightning can convert nitrogen gas into nitrates.
      • The very high electrical energy discharges from lightning activates nitrogen and oxygen molecules to react and form nitrogen oxides. These dissolve in rain to form nitrates which end up in the soil when rainwater trickles into the soil.
    • d) Action of decomposers: Their function is to break down dead animals and plants
      • Decomposers, e.g. various organisms like bacteria, fungi or worms can break down dead animals or plants. They break down proteins to amino acids.
    • e) Action of soil bacteria: Their function is to convert proteins and urea into ammonia or ammonium ions.
      • Decomposer bacteria in the soil can change proteins from dead plants/animals and urea in animal urine/droppings into ammonia/ammonium ion compounds.
      • d) plus e) is sometimes called putrefaction by putrefying bacteria.
    • f) Action of nitrifying bacteria: Their function is to convert this ammonia to nitrates - the process of nitrification
      • Nitrifying bacteria oxidise ammonia/ammonium ions from the decayed material to form nitrates, the nitrate ion can be absorbed by plants through their root systems.
    • g) Plants absorb nitrates from the soil.
      • Plants absorb nitrates (soluble in water) in the moisture that the roots absorb from the surrounding soil.
      • Plants can use the nitrate ion in forming amino acids from which the plant can make its proteins.
    • h) Nitrates are needed by plants to make proteins for growth.
      • Nitrates are an essential nutrient for plants to synthesis amino acids and hence proteins.
    • i) Nitrogen compounds pass along a food chain or web of food chains.
      • All food chains involve the passing of carbon compounds e.g. sugars, carbohydrates, fats and proteins up to the next trophic level i.e. the consecutive eating along a food chain (and waste produced on the way).
        • e.g. grass ==> cow ==> human
        • Plants make their own protein from nitrates, but animals must obtain it from plants or other animals. In fact the protein is broken down in digestion to amino acids and each animal makes its own proteins from these amino acid residues.
    • j) Action of denitrifying bacteria: Their function is to convert nitrates to nitrogen gas.
      • Particular bacterial organisms can remove the oxygen from nitrate compounds to form the element nitrogen gas.
      • These denitrifying bacteria live in anaerobic conditions like waterlogged soils and use the nitrate ion to respire.
      • This is the opposite function of the nitrogen-fixing bacteria (b).

 


Index: A Reversible Reactions  *  B Reversible reactions and Equilibrium 

C The Haber Synthesis of ammonia  *  D(a) The Uses of ammonia-nitric acid-fertilisers 

D(b) Fertilisers-environmental problems  *  E The nitrogen cycle 

(c) doc b Foundation tier (easier) multiple choice QUIZ on ammonia, nitric acid and fertilisers etc.

(c) doc b Higher tier (harder) multiple choice QUIZ on ammonia, nitric acid and fertilisers etc.

Advanced A Level Notes - Equilibrium (use indexes)

Advanced A Level Chemistry Notes p-block nitrogen & ammonia


gcse chemistry revision free detailed notes on nitrogen cycle to help revise igcse chemistry igcse chemistry revision notes on nitrogen cycle O level chemistry revision free detailed notes on nitrogen cycle to help revise gcse chemistry free detailed notes on nitrogen cycle to help revise O level chemistry free online website to help revise nitrogen cycle for gcse chemistry  free online website to help revise nitrogen cycle for igcse chemistry free online website to help revise O level nitrogen cycle chemistry how to succeed in questions on nitrogen cycle for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on nitrogen cycle to help to pass gcse chemistry questions on nitrogen cycle a good website for free help to pass igcse chemistry with revision notes on nitrogen cycle a good website for free help to pass O level chemistry keywords: N2 + O2 ==> 2NO + O2 ==> 2NO2 NO2 + water ==> nitrates (aq) in rain/soil Nitrifying bacteria lightning recycling nitrogen oxides denitrifying bacteria Nitrogen-fixing bacteria Leguminous plants legumes nitrogen fixation decomposers soil bacteria plants absorbing nitrates gcse chemistry revision free detailed notes on explain the circulation of nitrogen in the environment to help revise igcse chemistry igcse chemistry revision notes on explain the circulation of nitrogen in the environment O level chemistry revision free detailed notes on explain the circulation of nitrogen in the environment to help revise gcse chemistry free detailed notes on explain the circulation of nitrogen in the environment to help revise O level chemistry free online website to help revise explain the circulation of nitrogen in the environment for gcse chemistry  free online website to help revise explain the circulation of nitrogen in the environment for igcse chemistry free online website to help revise O level explain the circulation of nitrogen in the environment chemistry how to succeed in questions on explain the circulation of nitrogen in the environment for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on explain the circulation of nitrogen in the environment to help to pass gcse chemistry questions on explain the circulation of nitrogen in the environment a good website for free help to pass igcse chemistry with revision notes on explain the circulation of nitrogen in the environment a good website for free help to pass O level chemistry studying environmental science at Cambridge University, studying environmental science at Oxford University, studying environmental science at Durham University, studying environmental science at York University, studying environmental science at Edinburgh University, studying environmental science at St Andrews University, studying environmental science at Imperial College London University, studying environmental science at Warwick University, studying environmental science at Sussex University, studying environmental science at Bath University, studying environmental science at Nottingham University, studying environmental science at Surrey University, studying environmental science at Bristol University, studying environmental science at Cardiff University, studying environmental science at Birmingham University, studying environmental science at Manchester University, studying environmental science at University College London University, studying environmental science at Strathclyde University, studying environmental science at Loughborough University, studying environmental science at Southampton University, studying environmental science at Sheffield University, studying environmental science at Glasgow University, studying environmental science at Liverpool University, studying environmental science at Leeds University, studying environmental science at Queens, Belfast University, studying environmental science at Kings College, London University, studying environmental science at Heriot-Watt University, studying environmental science at Lancaster University, studying environmental science at East Anglia (UEA) University, studying environmental science at Newcastle University, studying environmental science at Keele University, studying environmental science at Leicester  University, studying environmental science at  Bangor University, studying environmental science at Nottingham Trent University, studying environmental science at Kent University, studying environmental science at Aberdeen University, studying environmental science at Coventry University, studying environmental science at Sheffield Hallam University, studying environmental science at Aston University, studying environmental science at Hull University, studying environmental science at Bradford University, studying environmental science at Huddersfield University, studying environmental science at Queen Mary, University of London University, studying environmental science at Reading University, studying environmental science at Glyndwr University, studying environmental science at Brighton University, studying environmental science at Manchester Metropoliten University, studying environmental science at De Montfort University, studying environmental science at Northumbria University, studying environmental science at South Wales University, studying environmental science at Liverpool John Moores University, studying environmental science at Central Lancashire University, studying environmental science at Kingston University, studying environmental science at West of Scotland University, studying environmental science at Lincoln University, studying environmental science at Plymouth University, studying environmental science at Greenwich University, studying environmental science at Liverpool Metropolitan  University,

ALPHABETICAL SITE INDEX for chemistry     

 For latest website updates see https://twitter.com/docbrownchem