Breathe Deep

Fact: Oxygen is a poison.

The air we breathe, the very thing keeping us alive… it turns out oxygen is actually poisonous to most life on Earth, including humans.

Oxygen is a critical reagent in the reaction we use to release energy from our food (‘respiration’). We do this by passing electrons from sugar molecules down a chain of proteins, releasing small amounts of energy with each step. Finally, that electron passes to an oxygen molecule, allowing us to safely get rid of it by breathing it out. If this chain gets backed up with used electrons we can’t make any more energy, which is why a lack of oxygen will kill you.

However, too much oxygen can do just as much damage, for the same reason it’s happy to pick up our discarded electrons – it’s very reactive. Millions of years ago, before plants roamed the Earth, there was no oxygen in the atmosphere. Life (which consisted only of bacteria at that point) was anaerobic, meaning it got its energy from other processes which don’t require oxygen to accept electrons.

However, when photosynthesis began oxygen gas began building up in our atmosphere: it’s so reactive that it attacked life on first sight, trying to strip away electrons from these bacteria and killing them in the process. In fact, the bacteria that live in our gut are anaerobic bacteria, which have settled down there in order to escape from the vicious wrath of oxygen so they can happily go on producing methane and spoiling your social situations.

Aerobic life (like plants and animals) evolved to use this oxygen to their advantage, and providing electrons for oxygen molecules to easily steal protects us from it damaging us too much. But even we have a limit: oxygen strips electrons off molecules to create dangerous ‘free radicals’ inside our bodies, and it is the damage that these radicals cause which drives ageing. So the secret to eternal youth is to avoid the one thing we can’t live without: the air we breathe.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license

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