Cellular respiration is the metabolic process in cells that help them create usable energy from nutrients such as food. The basic process of cellular respiration involves conversion of nutrients from food into ATP or adenosine triphosphate, which is a type of energy that can be used for various cellular processes.  Without cellular respiration, ATP or energy cannot be produced and no energy will be available to support the various cellular processes that are essential for the body.

In aerobic type of cellular respiration, oxygen is required to make this metabolic process work. Oxygen basically acts like a fuel for the cells in order to create usable energy which is ATP. Through normal breathing, oxygen will be taken in by the body through the different cells.  Oxygen will then help break down the components of food and convert them into ATP or energy stores.  These energy stores will then be used up for various processes like muscle activity and blood flow for example.  Another type of cellular respiration does not require the presence of oxygen to create energy. This type is called anaerobic respiration.  Nutrients from food are still processed.  Glucose or sugar for example will still be broken down to form energy but in more limited amounts because of the absence of oxygen.  The process of fermentation will then result to the build up ATP in anaerobic type of cellular respiration.

Non-complex organisms are those that may survive and thrive without requiring oxygen for cellular respiration. These simpler organisms do not require as much ATP or energy as human beings for example because they have basic requirements to survive.  In humans, both aerobic and anaerobic types of cellular respiration are needed depending on the requirements of the body.  For immediate needs of energy by the muscles for example, anaerobic cellular respiration provides just enough ATP for a specific muscular activity.  For long-term processes, oxygen is employed for higher and more efficient ATP or energy yield.