Cycling of Matter Biology: The Sustainability of Ecosystems (Grade 10)

Expectations By the end of this lesson, students will: Illustrate the cycling of matter through biotic and abiotic components of an ecosystem by tracking nitrogen

Nitrogen Nitrogen has the chemical symbol “N” A nitrogen atom has seven protons and seven electrons Most abundant element in the Earth’s atmosphere Source:

Investigating Air Mid-1700’s, chemists had separated air into two components: “fire air” (oxygen) and “foul” or “noxious” (nitrogen) air Nitrogen exists naturally in the planet’s atmosphere as nitrogen gas or diatomic nitrogen (N 2 ) Source:

Nitrogen All life on Earth requires nitrogen compounds (e.g. proteins, nucleic acids) Approximately, 78% of our atmosphere is nitrogen gas (N 2 ) However, most organisms can not use nitrogen in this form! Source:

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Nitrogen Fixation Large amounts of energy are required to convert N 2 into a more usable form, such as: ammonium ions (NH 4 + ) or nitrate ions (NO 3 - ) This process is called “fixing” Three processes are responsible for the majority of nitrogen fixation in the biosphere:  Atmospheric fixation  Biological fixation  Industrial fixation

Atmospheric Fixation In the presence of enormous energy, N 2 and O 2 react, to eventually produce nitric acid (HNO 3 ) The HNO 3 dissolves in the precipitation forming nitrates (NO 3 - ) and are carried to the ground This process is responsible for ~ 5-8% of nitrogen fixation Source:

Biological Fixation Colonies of certain bacteria are found in the roots of various plants and have the ability to fix nitrogen from the atmosphere E.g., the symbiotic relationship between Rhizobium and legumes Source:

Industrial Fixation Ammonia, NH 3, (gas or liquid) can be injected directly into the soil Ammonium nitrate is a powder which is spread on the soil and reacts with water to form ions Source:

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Decomposition The waste from animals, as well as the decay of their bodies after death, return nitrogen to the soil Micro-organisms and fungi break down the molecules in wastes and dead organisms into ammonia (NH 3 ) Source:

Nitrification Ammonia can be taken up directly by plants However, most of the ammonia is converted into nitrates by nitrifying bacteria Nitrification makes nitrogen more readily available for plants Source:

Denitrification Denitrifying bacteria convert nitrates (NO 3 - ) to nitrites (NO 2 - ) and then to nitrogen gas (N 2 ) Denitrification completes the nitrogen cycle Source:

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Eutrophication Anthropogenic eutrophication caused by runoff from agricultural farms, urban lawns, and golf courses Source:

Nitrous Oxide (N 2 O) Average life span of a N 2 O molecule = 120 years! A molecule of N 2 O traps 206 times more heat than a molecule of CO 2 ! Source: