Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: EvaH on 29/04/2020 10:36:21
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Andrew asks:
Why do we need oxygen? What does the body do with it? Is there anything else that could be used had we evolved differently?
What do you think?
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Animals work by getting energy from the combustion of carbon-containing molecules to produce principally carbon dioxide and water. Plants work by using sunlight to synthesise carbon-containing molecules from carbon dioxide and water.
It is arguable that a very different planet might evolve a parallel life with sulfur substituted for oxygen, and some microbes certainly seem to enjoy a sulfur-rich diet, but the surface temperature of this planet happens to be just right for the carbon-water-oxygen system, and the capability of carbon and hydrogen to form extremely complex and varied molecules is unique.
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Why do we need oxygen?
It depends on where you live.
At a very basic level, we need to use the stuff that is around us.
Oxygen is one of the most common elements in the Solar system (after hydrogen and helium). Oxygen is churned out by stars that are just slightly heavier than the Sun.
- Earth has lost most of it's hydrogen and helium (the most common elements in the universe)
- Other common elements on Earth besides oxygen are carbon (the basis of organic chemistry) and nitrogen (a major basis for proteins)
- Sulfur (as mentioned by Alan) is chemically similar to oxygen, but much less common in the Solar System. However, two amino acids (methionine and cysteine) do contain sulfur.
If we speculate about the possibility of life in far more extreme environments:
- Some of the moons of Jupiter and Saturn are thought to contain liquid water deep within. If life could exist there, oxygen in the water would play an important part in their biochemistry. But without photosynthesis to produce free oxygen (a very energetic process which produces a very unstable compound), oxygen would be unlikely to play a major role as an energy source.
- If life could exist on the cold surface of moons like Titan, most of the oxygen is bound up in rock-hard water ice (or rock-hard rock). Oxygen is unlikely to form a large part of their biochemistry
- The Sun is nearly all hydrogen and helium; if life could exist in the Sun, oxygen would play a small role.
- Neutron stars contain few light elements; if life could exist there, oxygen would play a small role.
See: https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Solar_system