PASSAGE 2:

You may think that people are capable of living in a wide range of environments, from the hot deserts of Africa and the Middle East to the freezing cold of Siberia or Northern Canada. Being an intelligent species, we worked out how to use fire to keep us warm in cold conditions and, considerably latre, air conditioning to keep us cool in hot climates. But there is a wide variety of organisms capable of living in environments in which no human could survivc___the cxtrcmophiles.

Take, for example, Spinoloricus cinzia, a tiny creature, about a millimeter long and looking a little like a jellyfish. This reccntly discovered animal is particularly intcrcsting, as it appears to be capable of living without oxygen and is thus a multi-cellular anaerobe.The cells of most organisms contain mitochondria, which use oxygen to generate energy, whereas the cells of Spinoloricus cinzia do not contain mitochondria. Most anaerobes so far discovered are microbes and use a form of fermentation to gain energy. Some anaerobes will actually die in the presence of oxygen.

What is the main purpose of the passage?