Molecular Advent Day 20: Oxygen

We each have an energy That affects the directions Of atoms, each other and Education With the infiltration of the digital age


Today’s molecule is here to remind you that despite the busy Christmas period you should still take time to Breathe! Dominique Skinner authors this piece on Oxygen:

We all need it to survive, but why do we need it and where does it come from?

Oxygen: a simple covalent molecule with two oxygen atoms bonded together by a shared pair of electrons (covalent bond). Although simple on a molecular level, it has the power to keep us alive and therefore deserves it’s fame.



21% of our atmosphere is oxygen and this oxygen is generated by plants in a photosynthesis reaction. This reaction takes carbon dioxide from the atmosphere and water, as well as light energy from the sun, to produce glucose as a food source and oxygen as a waste product. Just like plants use glucose and oxygen to produce energy, we do to. Plants produce more oxygen than they use and this is released into the atmosphere. We breathe the oxygen into our lungs where it is exchanged for carbon dioxide and used to produce energy. The process that takes oxygen and glucose and produces energy in the form of ATP is respiration; the opposite to photosynthesis. Once we have released carbon dioxide back into the atmosphere the cycle begins again.

Plants only photosynthesise during hours of sunlight, but like us they respire all the time. Photosynthesis occurs in the leaves of plants and therefore seems a little tricky in winter, right? Actually, plants take on a semi-dormant stage through winter as water underground can be frozen and photosynthesis isn’t feasible with the lack of sunlight. Therefore they remove their leaves as a way of survival. So, why don’t we run out of oxygen in the winter?

Thankfully, the earth always tries to run in balance and whist one hemisphere experiences winter with less plants producing oxygen, the other hemisphere experiences summer with more plants producing oxygen. This ensures the earth stays with around 21% oxygen in the atmosphere all year round.