Plankton

Plankton—often reduced to a mere word—actually produces about 50% of the oxygen we breathe and sequesters CO₂ by transporting it to the depths. Yet, this term conceals a staggering diversity of living things, ranging from invisible microbes to extraordinary organisms with radically different ways of life, reproduction, and adaptation. However, they are threatened by global warming, which could diminish the production of the oxygen we breathe. Pictures on YouTube.