<span>Grasslands are one of the most widespread of all the major vegetation types of the world. This is so, however, only because human manipulation of the land has significantly altered the natural vegetation, creating artificial grasslands of cereal crops, pastures, and other areas that require some form of repetitious, unnatural disturbance such as cultivation, heavy grazing, burning, or mowing to persist. This discussion, however, concentrates on natural and nearly natural grasslands.
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Los pulmones y el sistema respiratorio permiten la entrada del oxígeno del aire en el organismo, así como la expulsión de dióxido de carbono al espirar. La respiración es el término que se utiliza para denominar el intercambio de oxígeno procedente del entorno por el dióxido de carbono que se produce en las células.
<span>aerobic respiration requires oxygen.</span>
