When you eat food the first thing your body does with the food molecules is to break them down into smaller components through the process of digestion. Your intestine then absorbs these smaller molecules into the bloodstream. From there, cells take up the molecules and chemically burn them through the process of cellular respiration, an important part of metabolism, to provide for energy needs.
Misconceptions
It's common to hear the word "respiration" used to refer to the process of breathing. In chemical terms, however, respiration refers to a cellular process. On a cellular level, respiration occurs when cells chemically burn nutrient molecules -- the digestion products of carbohydrates, proteins and fats -- in the presence of oxygen to produce energy. Respiration is an important part of metabolism, which is the sum and total of all chemical reactions that take place in the body.
Metabolism
The human body runs many different chemical reactions, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." Some of these reactions result in breaking molecules down into smaller molecules -- as in the process of respiration -- and are called catabolic reactions. Other reactions build up molecules from smaller molecules, and are called anabolic reactions. Metabolism is the sum of anabolic and catabolic reactions in the body.
Purpose of Respiration
Cells burn molecules through the process of respiration to produce energy. In the same way that you burn wood in the fireplace to release heat, which is a form of energy, cells chemically burn glucose and other molecules that we obtain from food, to release energy. Just as your wood-burning fireplace needs oxygen to produce flame and heat, the cells require oxygen to chemically burn nutritional molecules, explain Garrett and Grisham.
Respiration Reactions
Respiration takes place through a series of reactions that vary with different nutritional molecules. Drs. Mary Campbell and Shawn Farrell explain in their book "Biochemistry" that one of the simplest respiration pathways is that through which your cells process glucose, which you obtain from carbohydrates. The cells break glucose into two molecules of pyruvate in a reaction series called glycolysis. The cells then burn the pyruvate molecules using oxygen through a reaction series called the Kreb's Cycle. These reaction processes yield energy.
Cellular Energy
When you burn wood in your fireplace, the energy from the wood is released as heat. When your cells burn molecules through respiration, some of the energy is released as heat, and this helps you maintain your body temperature. Some of the energy, however, your cells store in the form of chemical energy molecules called ATP. Muscle cells and other body cells can then use ATP to produce movement and engage in other cellular processes, explain Campbell and Farrell.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
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