Symbiosis

Soon after aerobic bacteria appeared, something special began to happen to life. Perhaps it began at the surface of the mud, where the anaerobes were still hiding away from the oxygen poison.

An anaerobe near the mud surface, in danger of being burned by free oxygen, passed its oxygen molecules (or oxidized molecules) and its own wastes to an aerobe in the water. In return the aerobe passed back molecules rich in the chemical life uses to store energy called ATP. Both bacteria gained. The aerobe got extra food. The anaerobe got energy.

When things live together like this, both benefiting from the arrangement, it is called symbiosis. Both partners benefit from the relationship. Neither could survive without the other.

A few of the many examples of symbiosis on Earth today are:

►    fungi and algae or blue-green bacteria live together in lichen

►    nitrogen-fixing bacteria live in the roots of beans

►    cows and the bacteria which live in their stomachs

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