Question not clear.
If you mean 'Why do climbers carry oxygen cylinders on mountains' then that is to survive. On high mountains like Mount Everest the air (oxygen) is so thin you need help to breathe, so they use oxygen from a cylinder.
No. They just take oxygen from the air.
the oxygen on a mountain is thinner than on the ground.
spacemen wear helmets because , there is no oxygen in space. They have to carry an oxygen cylinder on their backs.
Animals need oxygen to carry out life processes. Plants need carbon dioxide. Some animals and plants can use either if they need to.
The element we need to breathe is oxygen. It is essential for cellular respiration, where our cells convert oxygen into energy to carry out their functions.
Haemoglobin.
Plants need sunshine to carry out photosynthesis.
The higher you go up away from the Earth's surface, the less oxygen can be found in the air and more of gases we don't need to breathe in. So, as the mountaineer goes higher up, breathing becomes harder and your body works slowly, reducing reaction times. By carrying an oxygen tank, the mountaineer can always be breathing the perfect concentration of oxygen they need at all times.
Gills carry oxygen fish need directly from the water
Yes, you can carry an oxygen machine while traveling, but you may need to make arrangements with the airline or transportation provider beforehand.
Spacecraft need an internal oxygen supply to provide a breathable atmosphere for astronauts during space travel. Since there is no oxygen in space, spacecraft must carry their own supply to support human life. This ensures that astronauts have the necessary oxygen to breathe and carry out their activities while in space.