Cell Respiration

Homeostasis requires a constant supply of usable energy (ATP). Heterotrophs have 3 metabolic paths to make (ATP).


  1. Glycolysis (anaerobic) - all living things
  2. Citric acid cycle (aerobic) eukaryotes only
  3. Electron transport chain (aerobic)




  1. Adds phosphates to glucose which uses 2 ATPs


  1. Splits the phosphorylated 6-carbon sugar into two 3-carbon molecules and uses the energy in their bonds to make 4 ATPs


  1. Glycolysis reduces 2 NADs to 2 NADH2+


  1. The 3-carbon molecules are eventually converted to pyruvates.


  1. The allosteric enzyme, phosphofructokinase, is an important regulating part of glycolysis affected by both activators (ADP) and inhibitors (ATP, citric acid)


  1. Glycolytic efficiency is only 2% (14 kcal of a possible 686 kcal per mole of glucose)