The correct answer is - cyanobacteria.
The atmospheric oxygen came from the cyanobacteria. These were one of the earliest living organisms on Earth. The cyanobacteria was using photosynthesis in order to create its own food. The photosynthesis process requires sunlight, carbon dioxide, water, and oxygen. The oxygen is mostly released as a waste product from the process of photosynthesis, thus the cyanobacteria were literally releasing oxygen that was ending up into the atmosphere. As more and more cyanobacteria there were across the planet, more and more oxygen they were releasing into the atmosphere, slowly changing the composition of the atmosphere, and setting the basis of it as we know it now.
I think I might be a LITTLE later on this one... but it was recommended, it's Deutschland
Answer: Anaerobic respiration or Fermentation
Explanation:
When we are engaged in intense physical activity such as running or riding a bike, the muscles need energy to function and they get this from aerobic respiration.
They will quickly run out of the oxygen required to sufficiently use aerobic respiration however and will turn to anaerobic respiration which can produce energy in the absence of oxygen.
As the body uses anaerobic respiration however, lactic acid is produced and builds up in the muscles. It is this lactic acid that leads to the muscles feeling sore.
