B
The other choices are nitrogen sources for plants.
Explanation:
Plants absorb nitrates (NO₃) and nitrites (NO₂) from the soil. Plants utilize these nitrogen sources which they assimilate to make plant proteins, amino acids and nucleic acids. Animals get their nitrogen sources from proteins that they acquire from feeding on the plants. These proteins are broken down into amino acids and used to make animal proteins. The amino acids also provide nitrogen source for which nucleic acids are formed.
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The answer is definitely B.
<span>The relative number of mitochondria in a cell would be a general indicator of the extent of energy (ATP) producing occurring within that cell.</span>
<span>Mitochondria, during the oxidative phosphorylation, uses oxygen available within the cell to convert chemical energy to energy in a form usable to the host cell (ATP energy). The number of mitochondria in a cell can vary between different cell types. Cells which require more ATP will have more mitochondria (for example, liver cells can have more than 2000 mitochondria, heart muscle cells even more than 5,000 mitochondria).</span>
