Nitrogen Cycle Science 10

Life’s Macronutrients Carbohydrates – sugars and startches – C 6 H 12 O 6 – glucose – C 12 H 22 O 11 – sucrose Lipids – fats and oils – CH 3 CH 2 CH 2 COOH – butanoic acid (butter) – C 55 H 98 O 6 - unsaturated triglyceride Protein – muscle tissue and amino acids – CH 3 CHNH 2 COOH – alanine – C 10 H 17 N 3 SO 6 – whey

Nitrogen The big difference with the third macronutrient is the inclusion of nitrogen Despite the fact that we are surrounded by nitrogen gas (about 78%) plants and animals are unable to metabolize nitrogen gas Instead, nitrogen must be changed from nitrogen gas (N 2 ) into a useable form before it enters the food chain

Nitrogen Cycle

Nitrogen Fixation Nitrogen fixation is the first step in the process It removes nitrogen from the atmopshere (N 2 ) and changes it into ammonia (NH 3 ) This can occur due to lightning strikes (small amount) and in nitrogen fixing bacteria (Rhizobia) which live in the nodules of legumes (peas, beans, alfalfa and clover)

Nitrification Once the nitrogen has been fixed, it needs to be changed into another compound Ammonia is changed into nitrate compounds (NO 3 - ) which are then able to be used by plants Ammonia is obtained by nitrifying bacteria either through nitrogen fixation or decomposition

Consumption, Waste and Decomposition Once the plants have taken the nitrates and used the nitrogen to synthesize proteins, these nitrogen compounds can move through the food chain As with carbon compounds, these nitrogen compounds will be returned to the soil through waste and the decomposition of dead organisms Decomposers return nitrogen to the ground as ammonia

Denitrification In order to close the loop, the process of denitrification must also occur Denitrifying bacteria in the soil take nitrates and convert them back into nitrogen gas and return them to the atmopshere

Nitrogen Cycle

Aquatic Nitrogen Cycle Nitrogen in an aquatic ecosystem in introduced in two main ways: – Run off – nitrogen compounds from land ecosystems will enter waterways and provide nitrogen to the ecosystem – Cyanobacteria (blue-green algae) – completes nitrogen fixation in an aquatic ecosystem The remainder of the process is almost identical to the land based nitrogen cycle

Human Impacts The nitrogen cycle should be a closed loop within an ecosystem However, agricultural reduces the amount of decomposition that occurs within the ecosystem and therefore reduces the amount of nitrogen available in the soil As a result, farmers need ways to return nitrogen to the soil

Replenishing Nitrogen There are a few common ways to return nitrogen to the soil – Crop rotation (before the science was well understood) – Plant legumes – Artificial fertilizers As a result of artificial fertilizers, there is now more nitrogen present in most ecosystems than plants can absorb; this disrupts the balance within an ecosystem

Results of Excess Nitrogen Excess nitrogen in soil will result in acidic soil (nitric acid) and will not only damage plants but also dissolve metals into the soil Excess nitrogen compounds in the atmosphere will lead to acid rain (also nitric acid) which increases the acidity of waterways and the water table Excess nitrogen in an aquatic system will lead to eutrophication and algal blooms

Eutrophication & Algal Bloom Fresh water ecosystem – extra nitrogen results in a larger growth of surface plants – Underwater plants do not have enough light to complete photosynthesis – Decomposer populations explodes, reducing oxygen in the water – Consumers die due to reduced resources Marine ecosystem – Extra nitrogen will lead to an algal bloom (huge increase in algae population) – As algae die, they sink into colder waters and the decomposers work to break down the algae – The decomposers increase in population and use the available oxygen – Consumers die due to reduced resources

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