Class 11 Biology Respiration In Plants Glycolysis


  • The term glycolysis has originated from the Greek words, glycos for sugar, and lysis for splitting.
  • The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway.
  • Glycolysis occurs in the cytoplasm of the cell and it is the only process in anaerobic organisms.
  • Glycolysis is the process in which glucose, derived from sucrose, undergoes partial oxidation to form two molecules of pyruvic acid.
  • Glucose and fructose are phosphorylated to give rise to glucose-6- phosphate by the activity of the enzyme hexokinase.
  • Glucose-6- phosphate isomerises to produce fructose-6-phosphate by phosphogluco isomerase.
  • Fructose-6-phosphate converts to fructose 1,6, bisphosphate by phosphofructokinase-1.
  • The fructose 1, 6-diphosphate is split into dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (PGAL) by the enzyme triose phosphate isomerase.
  • Glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate by the enzyme glyceraldehyde 3-phosphate dehydrogenase.
  • 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase.
  • 3-phosphoglycerate is converted to 2-phosphoglycerate by the enzyme phophoglyceromutase.
  • Enolase converts 2-phosphoglycerate to phosphoenol pyruvate.
  • Pyruvate kinase converts phosphoenol pyruvate to pyruvate.
  • ATP is utilised at two steps: first in the conversion of glucose into glucose 6-phosphate and second in the conversion of fructose 6-phosphate to fructose 1, 6-diphosphate.
  • When 3-phosphoglyceraldehyde (PGAL) is converted to 1, 3-bisphosphoglycerate (DPGA), NADH + H+ is formed from NAD+.
  • Coversion of 1,3-bisphosphoglycerate and phosphoenol pyruvate to 3-phosphoglycerate and pyruvate, respectively, are energy-yielding process, where energy is trapped by the formation of ATP.
  • There are three major ways in which different cells handle pyruvic acid produced by glycolysis. These are lactic acid fermentation, alcoholic fermentation and aerobic respiration.
  • Fermentation is anaerobic respiration, whereas organisms adopt Krebs’ cycle which is also called as aerobic respiration.


Fig. Glycolysis

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