What Kind of Gases Do Living Organisms Require for Viability?

The Atmosphere

• Ninety-nine percent of the Earth's atmosphere is made up of either oxygen or nitrogen. If this were not the case, then life on Earth would not be possible, because living creatures depend on these two gases. Only about .0035 percent of the atmosphere is composed of carbon dioxide, but it is equally essential because plants use carbon dioxide in the process of photosynthesis. Since photosynthesis also releases oxygen back into the atmosphere, carbon dioxide is ultimately just as essential to life as oxygen is.

Oxygen

• Oxygen is the only gas that is used directly in the human body in its gaseous form. Animals take in oxygen when they breathe, and use it to convert food to adenosine triphosphate or ATP. ATP is the source for all the energy used in every activity, and the body couldn't make it without oxygen. No animal is capable of surviving for long without access to oxygen. A person deprived of oxygen will die within 10 minutes.

Nitrogen

• The air humans breathe is normally only 21 percent oxygen. Since the remainder is mostly nitrogen, the nitrogen serves to dilute the oxygen, even though the body don't use the nitrogen itself in that state. Instead, humans acquire nitrogen through the nitrogen cycle. This is a complex process in which rain or other precipitation carries nitrogen with it into the soil, from which it is absorbed by plants and transformed into protein. This protein is then consumed by the animals that eat the plants.

Carbon Dioxide

• Animals convert food into ATP through breathing oxygen, but plants and some types of bacteria use a different process called photosynthesis. In photosynthesis, chlorophyll inside the plant converts water and carbon dioxide into sugar and oxygen. The plant is able to convert the sugar into ATP, which it uses for energy just as animals do. The plant also releases the oxygen back into the atmosphere, contributing to the survival of all forms of animal life.