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Nitrogen Cycle • Describe the role of decomposers in the decomposition of organic material. • Describe how microorganisms recycle nitrogen within ecosystems. What is the Nitrogen Cycle? It is the recycling of nitrogen compounds! Why is it important? Nitrogen is a vital element in the production of proteins. Nitrogen cannot be utilised in its gaseous form so needs to be converted to other substances N2 in the Atmosphere How does this nitrogen get into the atmosphere? Denitrifying bacteria What do these bacteria do? They convert nitrates found in the soil into nitrogen gas Denitrification. • The process by which nitrates in the soil are converted into gaseous nitrogen. • It is carried out by the anaerobic bacteria Pseudomonas denitrificans and Thiobacillus denitrificans • They like water logged soil (anaerobic conditions) • Farmers and gardeners dig and plough their land to increase drainage and reduce anaerobic conditions. N2 in the Atmosphere Denitrifying bacteria Nitrogen fixing bacteria in roots Haber process Nitrogen fixing bacteria in the soil Lightning Nitrates in the soil How does lightning add nitrates to the soil?. • It splits nitrogen gas into nitrogen atoms which react with oxygen to form oxides of nitrogen. These then dissolve in rain water and eventually in the soil form nitrates. What are the names of some nitrogen fixing bacteria in the soil? •Azotobacter, Clostridium and Nostoc. What is the name of a nitrogen fixing bacteria in a root nodule? •Rhizobium. N2 in the Atmosphere Nitrates in the soil Denitrifying bacteria Produces ammonia and ammonium compounds which are used to make fertilisers Haber process Lightning Nitrogen fixing bacteria in roots Nitrogen fixing bacteria in the soil What does the Haber process do? N2 in the Atmosphere Nitrogen fixing bacteria in roots Denitrifying bacteria Haber process Nitrogen fixing bacteria in the soil Ammonia and Ammonium compounds Fertilisers Lightning What do the bacteria in roots do? They convert nitrogen gas in the soil into nitrogen compounds in the roots Why is this useful? Nitrates in the soil The plant can then make proteins. Nitrogen Fixation Converts gaseous nitrogen into a form which can be utilised by a plant. It is carried out by both free living organisms and organisms living in symbiotic association with leguminous plants. They increase soil fertility. N2 in the Atmosphere Nitrogen fixing bacteria in roots Denitrifying bacteria Haber process Nitrogen fixing bacteria in the soil Ammonia and Ammonium compounds Fertilisers Lightning Nitrates in the soil Plant proteins How else do plants get nitrates? They absorb them from the soil through their roots. How do animals get the proteins they need to grow? By eating plant material How are Nitrates added to the soil? Organic waste from dead animals or plants, or animal excretions contain useful nitrogen compounds and make good fertilisers if put on the soil. N2 in the Atmosphere Haber process Nitrogen fixing bacteria in the soil Animal protein Decomposition Ammonia and Ammonium compounds Decomposition Fertilisers Lightning Nitrifying bacteria Nitrogen fixing bacteria in roots Denitrifying bacteria Plant proteins Nitrates absorbed by roots Nitrates in the soil Nitrification This is the name given to the series of reactions involved in the oxidation of ammonia to nitrates. There are 2 stages: 1. The oxidation of ammonia or ammonium compounds to nitrites by free living bacteria e.g. Nitrosomonas 2NH3 + 3O2 2NO2- + 2H+ Ammonia Oxygen Nitrite + 2H2O Hydrogen ions Water 2. The oxidation of the nitrite by other free-living bacteria e.g. Nitrobacter and Nitrococcus 2NO2Nitrite + O2 Oxygen 2NO3nitrate In both cases chemosynthetic bacteria carry out these processes as a means of obtaining their respiratory energy.
