Cellular respiration is the process in which most eukaryotic organisms break down a glucose (C6H12O6) molecule releasing chemical energy. This energy is used by the cell to synthesize Adenosine Triphosphates (ATPs), which are small chemicals that the cell can directly use for energy to do work in the cell. All living organisms use ATP as a direct energy currency in the cell.
The overall chemical equation for cellular respiration is:
Our bodies (and nearly all living organisms) can use glucose as an energy source for the synthesis of ATP. When we eat glucose it enters into our digestive system via facilitated diffusion. In the presence of oxygen that we breathe, the three steps of cellular respiration are completed. This is the sole purpose for why we must breathe. Think of how much oxygen you breathe, and that is how many of these chemical reactions are occurring simultaneously (about a million ATP are created per second per active muscle cell!). The essential products of cellular respiration are the ATP. These are the chemicals that the cell uses to do the work of the cell. Waste products include carbon dioxide, which we exhale, and water, which we excrete. Nearly all eukaryotic organisms utilize this process.
Lab: Cellular Respiration
In this experiment, you will measure the rate of cellular respiration of germinating chick peas. How do we measure this process? If you refer to the general equation, we could measure the rate of cellular respiration by either (1) determining glucose intake, (2) measuring the intake of oxygen, (3) measuring the release of carbon dioxide, or (4) determining the production of heat (which is a byproduct of these chemical reactions). In this experiment, you will place respiring peas into an air tight chamber with a chemical, Potassium Hydroxide (KOH), that strongly binds to carbon dioxide (CO2), effectively removing CO2 gas from the chamber. In this air tight chamber, you will place dye into a thin, glass capillary tube. Changes in air pressure will be measured by how much the dye moves in the capillary tube.
Fermentation in yeast
Yeasts are eukaryotic, single celled fungi that lack mitochondria. Since they lack mitochondria, they are unable to go through the last two steps of cellular respiration: the citric acid cycle and the electron transport chain. Like cellular respiration, yeast are able to break down a glucose (C6H12O6) molecule and use the chemical energy released to synthesize ATP from ADP and P. However, this process yields far few synthesized ATP, a net of two ATP compared with cellular respiration’s net of 25ATP. Unlike cellular respiration, this process can occur in the absence of oxygen (O2).
The general equation for yeast fermentation is:
In yeast, two byproducts are given off and no longer utilized by the yeast: carbon dioxide and ethanol. The carbon dioxide gas given off by yeast causes bread to rise, and ethanol is what makes beer and wine alcoholic. When you bake bread, the temperature elevates above ethanol’s boiling point removing it from bread. In this experiment, we will detect the production of carbon dioxide as a byproduct of fermentation in brewer’s yeast.