What is the Fuel Used in Respiration?

Respiration is the process that occurs within the cells that makes energy from the food you eat. Food, therefore, is the fuel for respiration. The type of food you eat can dictate how much energy you get out of the food. Some foods are simply better fuels than others.

Function

Respiration under normal circumstances utilizes three processes: glycolysis, the Kreb's cycle and oxidative phosphorylation. In different manners, each of these steps uses nutrients from the food you eat and turns them into the energy that is required to maintain bodily functions and daily activity.

Types

Foods can be broken down into three types: carbohydrates, proteins and fats. Each type enters the respiration equation at a different place and in a different form.

Features

Proteins are made of up a series of amino acids connected together. The process of digestion breaks proteins apart into their constituent amino acids. Proteins that are to be used as fuel for respiration are converted to a substance called acetyl coenzyme A which enters the Kreb's cycle and produces ATP through oxidative phosphorylation. In general, you get four kilocalories of energy for every gram of protein you eat.
Carbohydrates are broken down into simple sugars and go through the process of glycolysis. Carbohydrates in excess of what the body needs as energy can be stored as glycogen in the liver and muscles, or can be converted and stored as fat. Similar to proteins, you get about four kilocalories of energy for every carbohydrate you eat.
Fats are broken down in the mitochondria of the cell into acetyl coenzyme A molecules and enter the Kreb's cycle, much like proteins. However, with each gram of fat you get nine kilocalories of energy. This means if you want to burn fat, it requires more than twice as many calories which is the reason that avoiding excess fatty foods is a sound part of a weight-loss plan.

Considerations

Aerobic respiration is the primary type of respiration animals undergo. This respiration takes place in the presence of oxygen, and more energy per molecule of fuel is produced (by about 20:1). Anaerobic respiration is respiration that takes place in the absence of oxygen. Some animal cells will occasionally do this, but generally speaking cannot do so for long periods of time. Many species of bacteria have the ability to respire without oxygen. Not as much energy is produced, but species undergoing anaerobic respiration can live in hospitable environments.

Geography

Respiration occurs within cells. Glycolysis occurs within the cytoplasm, and the Kreb's cycle and oxidative phosphorylation occurs in the mitochondria.