Characteristics of Living Organisms: Respiration

Respiration is the process by which energy is released from glucose for use in the body. This process can be aerobic or anaerobic.

Aerobic Respiration

This type of respiration requires oxygen. So in essence energy is released from glucose with the use of oxygen. The equation can be summarised below:


We obtain glucose from the food we eat and oxygen from the air we breathe; and carbon dioxide and water are released into the atmosphere when we exhale. Glucose and oxygen are used up and carbon dioxide and water are waste products. Energy is released in the form on ATP.

This type of respiration is an enzyme controlled reaction that occurs at all times inside cell organelles called mitochondria.

Please remember that respiration is NOT breathing. They are two completely different processes. Also, aerobic respiration is not limited to humans only; it occurs in plants as well.

Anaerobic Respiration

When there is not enough oxygen present, the body still needs energy to carry out its functions. This is where anaerobic respiration steps in. This type of respiration occurs in the absence of oxygen and plays a larger role in energy release during exercise.

This type of respiration is not effective.Glucose is not completely broken down and about 5% of the energy released per molecule of glucose in aerobic respiration is released in anaerobic respiration.


During exercise, the oxygen demand for the body (especially the muscles) is high. When oxygen becomes limited, anaerobic respiration kicks in and the glucose is broken down into the reaction (pictured above); the waste product is lactic acid rather than carbon dioxide and water. Lactic acid also happens to be poisonous for the body. After a period of anaerobic respiration, there tends to be a build up of lactic acid in the muscles. Lactic acid is poisonous and has to be removed from the body as soon as possible. For this to occur, oxygen is necessary. Using the exercising example above, once you stop to recover your breaths, and start taking in more oxygen to meet your body’s demands, then the switch to aerobic respiration is made and lactic acid is broken down in the muscles.

Bear in mind that anaerobic respiration can occur in plants as well.

The next topic in this “Characteristics of Living Organisms” series will be Excretion. If you have any questions or concerns about the post above don’t hesitate to comment below!


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