AP BIOLOGY

Detailed explanation-1: -Organizationally, the process is often divided into 8 steps, one for each controlling enzyme, usually beginning with the combination of the Oxaloacetate substrate to the Acetyl–CoA, which is produced from either glycolysis or pyruvate oxidation.

Detailed explanation-2: -In the citric acid cycle all the intermediates (e.g. citrate, iso-citrate, alpha-ketoglutarate, succinate, fumarate, malate, and oxaloacetate) are regenerated during each turn of the cycle.

Detailed explanation-3: -The eight steps of the citric acid cycle is a loop because the compounds used at the beginning are regenerated in the last stage to be used again.

Detailed explanation-4: -Out of the eight reactions of the citric acid cycle, there are four reactions considered oxidation-reduction reactions since the oxidation number of the species involved gets changed in these four reactions.

Detailed explanation-5: -Step 1: Acetyl CoA (two carbon molecule) joins with oxaloacetate (4 carbon molecule) to form citrate (6 carbon molecule). Step 2: Citrate is converted to isocitrate (an isomer of citrate) Step 3: Isocitrate is oxidised to alpha-ketoglutarate (a five carbon molecule) which results in the release of carbon dioxide.