Cellular Respiration

Cellular Respiration is a set of metabolic processes that occurs in a cell to produce ATP. As seen in the picture above, the process begins in the cytosol and then continues in the Mitochondria which can be found in nearly all Eukaryotic cells, including animal and plant cells.

A common misconception is that plant cells produce energy through their chloroplasts, whereas in reality the chloroplasts create glucose, which is then catalyzed during cellular respiration in the mitochondria to produce ATP.

Cellular Respiration occurs in two forms:

• Aerobic Cellular Respiration- energy produced in the presence of oxygen.
• Anaerobic Cellular Respiration- energy produced in the absence of oxygen.

Aerobic Cellular Respiration

This is the process by which energy is extracted from food in the presence of oxygen. This process occurs in several enzyme catalyzed steps, but the overall reaction is as follows:

C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6H₂O ΔG= -2870 kJ/mol

Essentially, glucose is burned/oxidized in oxygen to produce carbon dioxide, water and free energy (which is used to form ATP!) In an ideal world, where aerobic cellular respiration is done at its most efficient rate, 38 ATP molecules can be produced. Keep in mind the 2nd Law of Thermodynamics- lots of energy is lost at each step. With this in mind, 38 ATP is not very realistic.

Cellular Respiration occurs in four steps. (Each of the following is a hyperlink to a subpage)

1. Glycolysis

2. Pyruvate Oxidation

3. The Kreb's Cycle

4. The Electron Transport Chain

Anaerobic Cellular Respiration + Fermentation

Anaerobic Cellular Respiration is a very similar process to Aerobic Cellular Respiration, but uses another inorganic molecule other than oxygen as a final oxidizing agent.

Fermentation is glycolysis in the absence of oxygen. Glucose is catalyzed to produce carbon dioxide and ethanol (alcohol), and a small amount of energy. This is represented in the equation below (*Note the difference in energy between this and aerobic respiration!!!)

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ ΔG= -218 kJ/mol

Since energy production can be done in the presence or absence of oxygen, organisms can be classified into 3 types:

• Obligate Aerobes: Organisms that cannot live without oxygen. These organisms use aerobic cellular respiration exclusively, and includes all plants and animals
• Obligate Anaerobes: Organisms that cannot survive in the presence of oxygen. These organisms use anaerobic cellular respiration or fermentation to produce energy. These organisms are mostly prokaryotic cells and some eukaryotic cells which lack the typical mitochondrion.
• Facultative Aerobes: Organisms that can survive with or without oxygen, such as yeast and E. coli.

Textbook Practice

p.168-171#1, 2, 4, 5, 7, 8