Nitrogen •Makes up about 78% of the atmosphere •Nitrogen gas is colorless, odorless, and generally inert or unreactive. •Most organisms can’t use unreactive N2. •Nitrogen compounds are vital components of foods, fertilizers, and explosives. Nitrogen Compounds •Nitrogen must be converted to more chemically available forms for plants and animals to use. •N2 – atmospheric nitrogen •N2O – nitrous oxide •NH3 – ammonia •NH4 – ammonium •NO2 – nitrites •NO3 - nitrates Nitrogen Cycle •Describes how nitrogen (N2) moves between various reservoirs: •Plants •Animals •Bacteria •Atmosphere •Soil •Describes the processes by which those reservoirs exchange N2 into usable nitrogen Vocabulary •Reservoir – A place where anything is kept or stored. •Process - A series of actions that produce something or that lead to a particular result. Processes in the Nitrogen Cycle •Fixation •Nitrification •Assimilation •Ammonification •Denitrification Nitrogen Fixation •Process where N2 molecules in the air break apart and combine with other atoms to form ammonium or NH4. •Plant nutrients are the result of nitrogen fixation. •Nitrogen gets “fixed” when it combines with oxygen or hydrogen. 3 - Ways to “fix” Nitrogen 1.Atmospheric Fixation 2.Industrial Fixation 3.Biological Fixation Atmospheric Fixation •Energy from lightning breaks N2 molecules apart. •N2 atoms combine with oxygen forming nitrogen oxides (N2O). •N2O dissolves in rain, forming Nitrates (NO3). •Nitrates are carried to the ground by rain. Industrial Fixation •Under certain conditions industrial plants combine nitrogen and hydrogen to form ammonia (NH3). •Ammonia is used as a fertilizer. Biological Fixation •Free Living Bacteria – highly specialized bacteria live in soil and combines N2 with H2. •Bacteria fixes 30% of available N2. •Produces ammonium (NH4) •This is where most nitrogen fixing is completed. •Symbiotic Relationship Bacteria - bacteria live in root nodules of pulse family plants. •Provides plants with ammonia in exchange for the plant’s carbohydrates and a protected home. •Legumes fix 70% of available N2. Nitrification •Nitrifying bacteria in the ground combine ammonia with oxygen to form nitrites (NO2). •Another group of nitrifying bacteria converts nitrites to nitrates (NO3). •Green plants absorb nitrates (assimilation),which are eaten by consumers. Assimilation •NH4 Organic N2 •Organic N2 compounds –amino acids, chlorophyll, and nucleic acid •Produced when plants take up NH4 •Organisms near top of food chain eat plants taking up biologically fixed nitrogen. Ammonification •Part of the decay process •When a plant or animal dies or leaves waste products, decomposers like fungi and bacteria turn N2 back into ammonia . •Ammonia is absorbed and stored in the soil. Denitrification •Converts nitrates (NO3) in the soil to N2 •Denitrifying bacteria live deep in swampy sediments where O2 is not easily accessible. •These bacteria take O2 from nitrates leaving the byproduct nitrogen gas (N2). •Returns nitrogen to the atmosphere to begin the cycle again Human Impact on the Nitrogen Cycle •Cause - Use of synthetic (man made) nitrogen fertilizers •Effect - Fixes more nitrogen than all natural sources combined Negative Consequences of Excess Nitrogen •Excess N2 in groundwater can lead to cancer in humans and respiratory distress in infants. •Excess N2 in surface water can lead to nutrient over-enrichment causing: • fish-kill events • algal blooms changes in species •Creates the smog-component nitric oxide (NO)and nitrous oxide (N2O) •Can result in acid rain •Allows invasion by non-native plants into ecosystems •Creates the smog-component nitric oxide (NO)and nitrous oxide (N2O) •Can result in acid rain •Allows invasion by non-native plants into ecosystems Comments are closed.
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Erik E. Mason
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