Los mares primitivos eran ricos en sustancias alimenticias , pero no existía oxígeno libre, de modo que los primeros seres vivos aprovecharon la energía de los nutrimentos mediante una forma de respiración llamada anaerobia.
La respiración anaerobia no requiere oxígeno, utilizaotras sustancias como nitrógeno. La energía obtenida con este tipo de respiración es poca, pero permitió a las primeras células realizar sus funciones.
En la actualidad, los organismos de respiración anaerobia son algunas especies microscópicas pertenecientes a los reinos arqueobacteria y monera que viven en condiciones extremas.
Algunos organismos anaerobios son quimiosintéticos, pues producen sustancias orgánicas a partor de inorgánicas.
Hay tres tipos de organismos anaerobios: los que mueren en presencia de oxígeno (anaerobios forzosos), los que pueden vivir en presencia de oxígeno pero no lo utilizan (aerotolerantes) y los que pueden aprovechar el oxígeno si está presente (anaerobios facultativos).
Los seres anaerobios se encargan de reintegrar al medio las sustancias orgánicas de desecho, como organismos muertos, para así reciclar la materia en los ecosistemas y pueda ser aprovechada nuevamente.
También tienen respiración anaerobia las bacterias que producen el tétanosy el botulismo, enfermedades que pueden ocasionar la muerte de las personas.
¿Que otros procesos anaerobios existen y para que se utilizan?
Existen procesos metabólicos celulares en los que las sustancias órganicas, como la glucosa, se transforma en enrgía en ausencia de oxígeno y se denomina fermentaciones.
En la fermentación la energía obtenida es menor que en la respiración aerobia porque las sustancias alimenticias se degradan de manera incompleta.
Un tipo de fermentación, conocida como fermentación alcohólica, se utiliza para fabricar bebidas. Por ejemplo, de los ázucares del jugo de la uva y de los de cebada molida, por acción de las levaduras Saccharomyces se obtiene el alcohol que contiene el vino y la cerveza.
Durante el proceso de fermentación se observan burbujas que indican la formación de dióxido de carbono.
Otros tipos de fermentación son la acética y la láctica. En la fermentación acética se convierte, por ejemplo, el vino en vinagre por la acción de las bacterias Acetobacter. En la láctica, las bacterias llamadas lactobacilos procesan la lactosa (azúcar de la leche) para acidificar la leche y producir yogur.
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