EVERYDAY SCIENCE

Detailed explanation-1: -Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen. But most organisms cannot use nitrogen in this form. Figure 7.2.

Detailed explanation-2: -nitrogen cycle, circulation of nitrogen in various forms through nature. Nitrogen, a component of proteins and nucleic acids, is essential to life on Earth. Although 78 percent by volume of the atmosphere is nitrogen gas, this abundant reservoir exists in a form unusable by most organisms.

Detailed explanation-3: -By far the largest reservoir of total nitrogen on Earth is the dinitrogen gas (N2) in the atmosphere (Table 4.1). N2 is also the major form of nitrogen in the ocean.

Detailed explanation-4: -Nitrate is the form of nitrogen most used by plants for growth and development. Nitrate is the form that can most easily be lost to groundwater. Ammonium taken in by plants is used directly in proteins. This form is not lost as easily from the soil.

Detailed explanation-5: -Biological nitrogen fixation: We already know that nitrogen is not used directly from the air by plants and animals. Bacteria like Rhizobium and blue-green algae transform the unusable form of nitrogen into other compounds that are more readily usable.