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<blurb target="nitro" width="420">
<short><![CDATA[The atmosphere represents a very large pool of nitrogen — nitrogen gas makes up more than three quarters of our atmosphere. A molecule of nitrogen gas consists of two atoms of nitrogen bonded together (N2). In this form, nitrogen is unavailable to plants and animals.]]></short> </blurb>

<blurb target="fixation" width="420"><short><![CDATA[Certain microbes have the ability to “fix” or convert nitrogen from the atmosphere into ammonia (NH3), a form that can be used both by themselves and by plants. Plants in the legume family have developed a close relationship with some of these bacteria. The bacteria live in special nodules on the plants’ roots where they receive food from the plant and provide usable nitrogen in return.]]></short></blurb>

<blurb target="microbe" width="420"><short><![CDATA[With the exception of the nitrogen-fixers, microbes must obtain nitrogen compounds from the soil or water in which they live. Microbial growth is often limited by a lack of nitrogen. Many microbes have thus developed an ability to convert nitrogen from one form to another, so they can take advantage of whatever form is most available.]]></short></blurb>

<blurb target="compound" width="420"><short><![CDATA[Two key microbial processes in the nitrogen cycle are nitrification and denitrification. In nitrification, bacteria convert ammonium ions (NH4+) to nitrite (NO2-) and then to nitrate (NO3-), which is also a form that can be absorbed by plants. In denitrification, bacteria convert nitrate to nitrogen gas, thus removing nitrogen from the soil or water and returning it to the atmosphere.]]></short></blurb>

<blurb target="chemical" width="420"><short><![CDATA[Humans frequently add nitrogen compounds to the soil to encourage plant growth. Animal wastes are one source of nitrogen-rich fertilizer. People have also found industrial ways to fix nitrogen gas. However, not all of the nitrogen in fertilizers reaches plants. Some is quickly converted to nitrogen gas and returned to the atmosphere, while some washes away in surface runoff or leaches into groundwater.]]></short></blurb>

<blurb target="dead" width="420"><short><![CDATA[Nitrogen stored in the tissues of plants and animals is released when an organism dies and decays. Bacteria and fungi are the main decomposers, breaking down the dead organism into smaller and smaller pieces. Some of the nitrogen is released to the environment as a byproduct of decomposition.]]></short></blurb>

<blurb target="chicken" width="420"><short><![CDATA[As an essential component of DNA and proteins, nitrogen is the fourth most common element in living cells, after oxygen, carbon, and hydrogen. Plants obtain nitrogen from the soil or from nitrogen-fixing bacteria. Animals must get all their nitrogen from the food they eat.]]></short></blurb>

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