Cellular respiration is a chemical reaction that occurs in all organisms. During cellular respiration, glucose(which is obtained from food or photosynthesis) is converted into ATP energy, which is used to power the functions and processes that occur in organisms. Cellular respiration takes place partly in the cytoplasm, and mostly in the mitochondria of eukaryotic cells.

The Chemical Equation for Cellular Respiration

Cellular respiration uses glucose and oxygen as reactants to produce the products water, carbon dioxide, and ATP energy. The equation is written below.

C6H12O6 + 6O2 → 6H2O + 6CO2 + ATP Energy

(Glucose)           (Oxygen)      (Water)    (Carbon Dioxide)

The Three Stages of Cellular Respiration

There are three stages of cellular respiration: glycolysis, the Krebs cycle, and the electron transport chain.

Glycolysis

Glycolysis occurs in the cytoplasm of cells. During glycolysis, glucose is broken down into two pyruvic acid molecules(2C3H4O3). As a result of glycolysis, two ATP molecules are made. The two pyruvic acid molecules then move on to the next stage of cellular respiration.

The Krebs Cycle

The Krebs Cycle is a cycle with 8 steps, in which a new molecule is created in each step by altering the old molecule. The two pyruvic acid molecules from glycolysis are made into molecules called Acetyl Coenzyme A. These molecules are added to oxaloacetate(which is a molecule made in the 8th step of the cycle) to make Citric Acid. The citric acid then gets changed into different molecules. The altering of the molecules in each step allows new important molecules to be created, like NADH and ATP.

The cycle repeats over and over again, with important molecules being made each time.

 

The Electron Transport Chain

The electron transport chain is a system that transports electrons in NADH through different molecules in the inner membrane of the mitochondrion. Throughout this process, hydrogen ions move from one side of the membrane(the matrix) to the other side, resulting in more hydrogen ions on one side of the membrane than the other. This causes a buildup of potential energy, which is used by a molecule called ATP synthase to combine ADP and phosphorous into ATP.