Using and making oxygen
The oxygen balance.
Breathing and burning
Animals breathe, wood burns, and plants grow, all in the same air.
Which of these puts oxygen back into the air?
What this lesson covers
The idea
Oxygen makes up 21% of the atmosphere and also exists combined in oxides, minerals and CO2; respiration and combustion consume O2 and release CO2, photosynthesis restores O2, and this balance circulates oxygen through all spheres.
Breathing and burning
Animals breathe, wood burns, and plants grow, all in the same air.
Which of these puts oxygen back into the air?
- Plants making food
- Breathing
- Burning wood
Takes oxygen, gives oxygen
Put each process in its group.
A balance
Oxygen is used by respiration and by burning, and it is made by photosynthesis. The balance between using and making keeps oxygen going round through the air, land, oceans and living things.
Oxygen makes up 21% of the atmosphere and also exists combined in oxides, minerals and CO₂. Respiration and combustion consume O₂ and release CO₂; photosynthesis restores O₂. This balance circulates oxygen through all the spheres.
Notes
Respiration and combustion use O₂ and release CO₂; photosynthesis restores O₂. This balance circulates oxygen (21% of air) through all the spheres.
Check yourself
What share of the atmosphere is free oxygen gas (O₂)?
Which process restores oxygen to the atmosphere?
Which of these uses oxygen and releases CO₂?
Besides free O₂, in which forms does oxygen exist?
- About 21% — correct. Yes!
- About 78%. About 78% of the atmosphere is nitrogen.
- About 1%. Oxygen is about 21% of the atmosphere.
- Respiration. Respiration uses oxygen and releases CO₂.
- Photosynthesis — correct. Yes!
- Combustion of fuels. Combustion of fuels uses oxygen and releases CO₂.
- Photosynthesis. Photosynthesis uses CO₂, sunlight and water and releases O₂.
- Nitrogen fixation. Nitrogen fixation converts N₂ into ammonia. It is not one of the processes the chapter lists for using oxygen.
- Respiration and combustion — correct. Yes!
- In metal oxides and minerals in the Earth's crust, and in CO₂ in the air — correct. Yes!
- Only as free O₂ in the air. Oxygen also exists in combined forms, in the crust as metal oxides and minerals, and in the air as carbon dioxide.
- Only in the oceans. Oxygen exists in the air, in the Earth's crust and in living things, in free and combined forms.