These processes however differ in their reactants, products, stages, requirements, organisms and organelles in which they occur (Photosynthesis vs. Respiration 2012).
Respiration is the set of chemical reactions in the cell cytoplasm and mitochondria that break-down sugars (glucose) in the presence of oxygen into energy in form of adenosine tri phosphate (ATP) and carbon IV oxide (Respiration 2014). This series of aerobic reactions are summarised in the chemical equation below; -
a) Glycolysis; - This is the break-down of glucose, a six carbon compound to pyruvate, a three carbon compound in the cytoplasm, a process that yields two ATP molecules (Photosynthesis vs. Respiration 2012). A glucose (C6) molecule is energized by the addition of a high-energy phosphate from ATP, forming glucose-6-phosphate which is re-arranged split into two Glyceraldehyde-3-Phosphate (C3); each Glyceraldehyde-3-Phosphate contributes 2 electrons to NAD+, an electron carrier as two (2) low energy Adenosine di phosphate (ADP) molecules are elevated to Adenosine tri phosphate (ATP) by addition of inorganic phosphate leaving pyruvate (University of Chicago at Illinois 2009).
b) Krebs cycle; - Pyruvate from glycolysis is converted into Acetyl-coA which is shuttled into the Krebs cycle in the mitochondria. Acetyl-coA through interconversion of 4C compounds gives off two (2) Adenosine tri phosphate (ATP) molecules, eight NADH and two FADH2 (University of Chicago at Illinois 2009).
c) Electron transport chain; - The ten molecules of NADH and FADH2 from the Krebs cycle are broken down in the mitochondrial matrix to form Adenosine tri phosphate (ATP); a process powered by an H+ proton gradient across the inner mitochondrial membrane and the matrix (Photosynthesis vs. Respiration 2012). The enzyme ATP Synthase powers the formation of ATP by reducing the proton gradient through electron transport. The