_____ is a layer of air (gases) surrounding the Earth.

_____ respiration is the process of obtaining oxygen from the atmosphere and eliminating carbon dioxide.

Which of the following process does not need oxygen?

_____ is used in astronaut's attire.

Oxygen combines with _____ chemically to form water.

Oxygen cycle maintains the amount of _____ in the atmosphere.

Which of the following is a property of carbon dioxide?

When carbon dioxide is present, lime water turns _____.

Carbon cycle maintains the amount of _____ in the atmosphere.