What is free nitrogen? Nitrogen gas is called "free" nitrogen, meaning it is not combined with other kinds of atoms. Most organisms can use nitrogen only once it has been "fixed," or combined with other elements to form nitrogen-containing compounds.

About 78% of the Earth's atmosphere is made up of "free" nitrogen (N2), produced by biological and chemical processes within the biosphere and not combined with other elements. ... One family of nitrogen compounds produced by nitrogen - fixing bacteria are called nitrates.

Explanation:

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blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

there's no big difference.

explanation:

the only little different between a rabbit and bunny is just that bunnies are much smaller than rabbits. bunnies are basically baby rabbits.