When living beings require energy, they require oxygen for breathing. The form in which oxygen is released back into the environment is carbon dioxide.
What is spacecraft?
A vehicle built for use outside the atmosphere of the planet.
In pressurized tanks located outside the airlock of the station, the ISS gets a regular supply of oxygen from the planet.
These aren't enough to keep the station stocked for a long time, but they are plenty to keep topping the tank off because there are occasionally leaks.
Hydrogen and carbon dioxide combine to form biomass when oxygen is released into the environment.
Living beings need oxygen for breathing when they require energy. Carbon dioxide is the form in which oxygen is released back into the atmosphere.
Hence, oxygen is a must in the air supply aboard spacecraft,
To learn more about the spacecraft refer;
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