What are the components of the Nitrogen cycle? WILF Recall why nitrogen is needed by living organisms Describe the organisms, compounds and processes involved in the Nitrogen cycle. Explain the role of different groups of organisms in the conversion from one compound to another. WALT 05 May 2015`

An overview of the Nitrogen Cycle Nitrogen does not easily react but it needs to be made into different compounds before it can be used by living things. NC involves three types of bacteria Nitrogen fixing bacteria convert nitrogen gas to ammonia Nitrifying bacteria convert ammonium to nitrate Denitrifying bacteria convert nitrate to nitrogen gas

Nitrogen-Fixers Rhizobium is found in root nodules of a group of plants called legumes. This includes clover; lupins; beans and peas (Soya) Azotobacter is found free living in the soil. They take in atmospheric nitrogen (N 2 ) and convert it to nitrogen containing compounds ammonium (NH4 + )

Processes in the nitrogen cycle Ammonification (putrifaction) Decomposers (Bacteria and Fungi in the soil) break down nitrogen rich proteins; amino acids and urea / uric acid from the bodies of animals and plants. These are converted into Ammonia (NH 3 ) or ammonium compounds (NH4 + ) It is what causes dead organisms to smell bad.

More processes Nitrogen Fixation The removal of nitrogen gas from the atmosphere and assimilation into the body of a living organism. Which group of living organisms will absorb the products of this process? Plants, through their roots. They can only absorb nitrogen in the form of nitrate. Into which organic compound (s) is the inorganic nitrogen fixed ? Proteins and amino acids

Nitrifying Bacteria Nitrobacter & Nitrosomonas convert Ammonia (NH 3 ) into Nitrites (NO 2 ) & then Nitrite (NO 2 ) to Nitrate (NO 3 ) They need oxygen rich soil or water to survive. What type of respiration does this group of bacteria carry out? Aerobic respiration. Which term would you use to describe them? Obligate aerobes

De-nitrifying bacteria Pseudomonas bacteria Do not need oxygen & are found in waterlogged soil Convert Nitrate into atmospheric nitrogen gas. Explain why farmers need to ensure good drainage for their crops to flourish.

Nitrogen and Living Organisms 1.Where do plants obtain their Nitrogen? By absorbing Nitrate (NO 3 ) from the soil / Through their roots/ by active transport 2.What do they do with it? Combine with glucose to make protein / amino acids 3.How do animals obtain Nitrogen? By eating the plants / food chain 4.How is this returned to the environment? Urea / excretion; death and Decay; Decomposers/ Bacteria and fungi

One other event helps to fix nitrogen Lightning provides the energy to react oxygen and nitrogen together to form nitrates

The Haber process This takes atmospheric nitrogen and converts it into artificial fertiliser. What role does farming play in the nitrogen cycle? The Haber process removes Nitrogen from the atmosphere to be converted to Nitrate in artificial fertiliser. Farmers spread this on their land for their plant crops to use as a source of nitrogen. The plants make organic nitrogen containing molecules (amino acids and protein) to help them grow. Plants are harvested, not left to decay. The land would be depleted of nutrients ater a growing season so the farmer as more manure or artificial fertiliser. Land needs to be ploughed regularly to maintain aeration. If let waterlogged, it promotes the action of denitrifying bacteria which would remove nitrogen from the system back into the atmosphere.

Describe how nitrogen is cycled in the biosphere. [10] ANitrogen gas in the atmosphere is fixed by Nitrogen-Fixing Bacteria Bwhich are either free - living in soil Cor in root nodules of legumes D(Nitrogen in the form of) amino acids and/or proteins ENitrogen is passed to animals during feeding F (Nitrogen in form of )urea / ammonia GNitrogen passes to soil during excretion HDead plants and animals are decayed by bacteria and/or Fungi. IDecay releases ammonium (compounds)/ammonia. JAmmonium (compounds) are converted to (nitrogen in the form of) nitrates KPlants (are only able to absorb) nitrogen in the form of nitrates. LPlants fix nitrogen in the form of amino acids and proteins.( ie inorganic to organic form) MDenitrifying bacteria/denitrification break(s) down nitrates and return nitrogen to the atmosphere. NLightning may cause nitrogen gas to react with oxygen in the air to from nitrates. Industrial production of fertiliser(e.g. Haber)

(i) Explain why nitrogen is important to living organisms. [2] (ii) Give an account of the different bacteria and their importance in the nitrogen cycle. [8] (max. 6 for well annotated diagram) ANitrogen is needed to synthesise amino acids (which are built into proteins.) BAny sensible e.g. of protein use - antibodies/membrane proteins/ enzymes. CUse of nitrogen to synthesise nucleic acids/DNA/RNA/ATP/ chlorophyll [2 max.] DThe nitrogen fixing bacteria. EConvert atmospheric nitrogen into nitrogen containing compounds/ammonium/amino acids (not: nitrates). FThis may be by free living bacteria in the soil. GOr by bacteria living in the root nodules of HLegumes/peas/beans/clover/lupins. IDecomposers/putrefying/decay bacteria convert organic nitrogen from dead organisms/ nitrogenous excretory products/urea/uric acid. JInto ammonia. KThe nitrifying bacteria convert this ammonia into nitrites. LAnd the nitrites into nitrates, which can be absorbed by plants. (equivalent) MThe denitrifying bacteria convert nitrates into atmospheric nitrogen. NThis is a problem in water logged soils since the bacteria are anaerobic. PWhich is why farmers drain wet land in order to increase soil fertility. [8 max.]